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© MOTOROLA LTD.2003 CDMA02: Principles of CDMA Page 1 / 425 FOR TRAINING PURPOSES ONLY

Section 1

Introduction to CDMA

South Asia Network Solutions Division Bangalore, India

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Section 1 Introduction to CDMA 1 Objectives 3 Wireless Local Loop 4 Multiple Access Methods 8 CDMA Concept 11 Concepts of Spread Spectrum Techniques 13 Basic Model of Anti Jamming System 15 Features of CDMA 17 CDMA Standards-Introduction 19 Frequency Re-Use 21 Capacity of CDMA Systems 23 Applications of Spread Spectrum Systems 25


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Objectives _____________________________________________________________ Objectives

Upon completion of this section, the trainee is expected to be able to:

Explain with suitable diagram the concept of the wireless local loop and

its advantages. Define Multiple Access methods and explain the concept of CDMA. List the features and advantages of CDMA. List CDMA standards. Explain frequency re-use. List applications of spread spectrum systems.


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Wireless Local Loop

_____________________________________________________________ Local Loop

The section between local exchange and the subscribers connected to it is called the local loop. In PSTN, the local loop is predominantly copper. If it is replaced by Optical fiber, we get Fiber in local loop. When a subscriber is ON HOOK, the telephone instrument extends a high ohmic resistance (10~15 KΩ) and low current flows on the line. When the subscriber goes OFF HOOK, the high resistance is replaced by a low ohmic resistance (~1000Ω), which results in an increase in the line current. This is sensed as a call attempt by the subscriber and the exchange extends the dial tone. We can say that the LOOP is closed. Thus, for every subscriber connected to the exchange, the local loop is extended through a pair of conductors. The local loop is made up of primary cables, secondary cables and Distribution cables.

Wireless Local Loop

If the local loop is extended from the subscriber’s premises to the exchange through Radio, the local loop is called Wireless Local Loop.


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© MOTOROLA LTD.2003 CDMA02: Principles of CDMA FOR TRAINING PURPOSES ONLY

Local Loop and Wireless Local Loop

BSC

Wireless Local Loop: Uses frequencies

Local Loop: Maup of Primary/Distribution cab

/Seconda


PSTN

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Wireless Local Loop _____________________________________________________________ Limitations of Wireline Local Loop

The copper based local loop as described in the foregoing section has a number of limitations such as:

High costs of implementation Longer duration of implementation Fault Proneness Long restoration periods Need for over building (provision of extra pairs at every point

to take care of future growths.) Advantages of Wireless Local Loop

The Wireless local loop, of any type of technology, has certain advantages over the wire line, which are tabulated opposite.

Specifically, wireless access to the network is advantageous both for high density areas where laying of cables is very difficult owing to restrictions by the local authorities and also remote areas where laying of cables is very expensive.


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Advantages of the WiLL

Features Benefits Flexible Deployment • Exact location of subscriber is not critical Less Investment • No need to overbuild

• Less susceptible to damage or theft • Low operational and maintenance costs.

Fast Deployment • Quicker accrual of Revenue • Useful in areas where terrain is difficult or places

where laying of copper is very difficult or not allowed. ( e.g., central parts of big cities )

Improved Availability • Lower losses due to interruptions. • Improved customer Satisfaction • Better Image. • Growth in Subscriber base.

Better Reach • Reliable service in Rural areas too.


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Multiple Access Methods _____________________________________________________________ Multiple Access Method

We define multiple access as a “ method by which a number of users try to access the available medium or bandwidth at the same time”.

In a simple way one can say that this determines the capacity of a network. (If more people can access the network at the same time, we say that the network has more capacity).

Types of Multiple Access There are three main types of Multiple Access

1. FREQUENCY DIVISION MULTIPLE ACCESS (FDMA):

Every user (or circuit) is assigned a specific frequency slot i.e. a number of frequencies are transmitted at the same time. This is being done in the AMPS mobile phone system in the US and was used in the analog mobile systems in the European countries.

2. TIME DIVISION MULTIPLE ACCESS (TDMA):

Here a number of users access the given bandwidth one at a time for a specific duration at the same frequency. I.e., each user is assigned a specific TIME SLOT at a particular frequency. If more capacity is needed, then we use more frequencies each with a number of time slots. This is used in the GSM systems.

3. CODE DIVISION MULTIPLE ACCESS (CDMA):

Here a number of users transmit at the same time at the same frequency. The individual users are identified by a specific code assigned to them. The code assigned is unique to each user. The signals are separated at the receiver by using a correlator that accepts only signal energy from the desired channel. Undesired signals contribute only to the noise.

The multiple access methods described above are illustrated in the page opposite.


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Multiple Access Methods

• N Users / Wideband Channel • C/I is still negative after I.F. filtering but positive after despreading process • Can consider despreading as the last "filtering" stage

• 3 Users / Narrowband Channel • C/I is negative prior to I.F. filtering and positive after filtering

123

1

TDMA (3 timeslots shown)

30 kHz

Frequency

Time

• 1 User/ Narrowband Channel • C/I is negative prior to I.F. filtering and positive after filtering

FDMA

30 kHz

Frequency

Time

DS-CDMA1.23 MHz

Frequency

Time

© MOTOROLA LTD.2003 CDMA02: Principles of CDMA Page 10 / 425 FOR TRAINING PURPOSES ONLY South Asia Network Solutions Division Bangalore, India

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CDMA Concept

_________________________________________________________ Spread Spectrum Signal

The spectrum of the speech signal from a user is SPREAD by multiplying it with a unique code which is at a much higher bit rate. The resultant signal is called a “SPREAD SPECTRUM” signal.

CDMA Concept In CDMA, a number of users communicate simultaneously at the same frequency. The spectrum of the base band signal is spread over a wider band by multiplying it with a Pseudo Random Signal. The CDMA concept is similar to the situation in a “Cocktail Party” where all the people talk in the same room together simultaneously. If every conversation in the room carried out in a different language, that you do not understand would amount to noise from your perspective. But the conversations in your language will be interesting to you. Even with knowledge of appropriate language, the conversation of interest may not be completely audible. The listener can signal the speaker to speak more loudly and also signal other people to speak more softly. CDMA system uses a similar power control process.

As the signal is transmitted, similar signals from other users in the area, external noise and other forms of noise get added to it. The sources of interference in CDMA are:

1. External Interference a. Background Noise b. Interference due to users from other cells

2. Internal Interference a. Other users in the same cell

The dominant source of interference is the self-interference produced by other users of the same cell.

At the receiving end we recover the wanted signal by multiplying it with a replica of the code used in the transmitting end.

The capacity of the system is self limiting as the overall interference level crosses a threshold.

This idea is illustrated in the diagram opposite.


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CDMA concept

Input Data

Spread Spectrumof Data

Spectrum at theReceiver input

Recovered Data

Back ground Noise External Noise Interfering Spectra

BPF BPF

PN-Sequence PN-Sequence

Dig.Filter


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Concepts of Spread Spectrum Techniques

_________________________________________________________ History

Spread Spectrum techniques are developed as a means to combat the effects of jamming of radio signals. The fundamental question that these systems try to answer is “ How can a receiver nullify the effects of jamming, if the jammer has more power than the transmitted signal?” The answer lies in the “White Noise” or the “Gaussian Noise”.

Concept of Spreading Spectrum Techniques

Since the Gaussian Noise has infinite power and is spread uniformly over the entire frequency spectrum, it is possible to have effective communication because only finite power signal components can cause any harm. Hence, the design of anti-jam system is to spread the signal spectrum sufficiently so that all interfering signals appear as noise. The signal components (e.g. frequency) are chosen such that the jammer or interferer cannot achieve larger jammer to signal ratios in the selected frequency components. Only finite power components of jamming signals affect communication and effective communication is possible in the presence of Gaussian Noise. The basic idea is to choose the number of signal co-ordinates N so that the jammer is uanable to pump large powers in all of them. N is made large by spreading the signal spectrum through one of the following methods:

• Direct Sequence Spreading (DS): A carrier is modulated by a digital code in which the code bit rate is much larger than the information signal bit rate.

• Frequency Hopping Spreading (FH): The carrier frequency is shifted in discrete increments in a pattern generated by a code sequence. This can be either fast-hop or slow-hop system. In fast-hop system, frequency hopping occurs at a rate faster than the message bit rate. In a slow-hop system, the hop rate is slower than the message bit rate

The CDMA system used in our networks use the Direct Sequence Spreading technique. The spreading is achieved by multiplying the base band signal with a Pseudo random signal (PN Sequence). The assumption is that the jammer does not have the key to the PN sequence. Hence, the jammer is forced to adapt the first jamming option mentioned above which reduces the jamming signal strength in the actual signal co-ordinates under use .


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Concepts of Spread Spectrum Techniques

• Spread Spectrum is basically an ANTI-JAMMING system • Only finite power components of signal are affected by jammer. So,

Effective communication is possible in the presence of Gaussian Noise

• The basic idea is to choose the number of signal co-ordinates N so that the jammer is unable to pump large powers in all of them

• N is made large by spreading the signal spectrum through:

o Direct Sequence Spreading (DS) or o Frequency Hopping Spreading (FH)

• Direct Sequence Spreading is used in commercial CDMA systems

• The spreading is done by multiplying the signal with a Pseudo random

signal (PN sequence) and it is assumed that the jammer does not know the key to the PN sequences employed


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Basic Model of Anti Jamming System

_________________________________________________________ Basic Model

The basic system model shown in the opposite page has the following parameters fixed:

WSS = Bandwidth of the spread out signal Rb = Bit Rate of base band signal PS = Signal Power PJ = Jammer Power Then Eb can be got from (PS / Rb) and NJ from (PJ / WSS) (WSS / Rb) This gives Eb / NJ = (PJ / PS) Where, we define Processing Gain PG = WSS / Rb Expressing in dBs, (Eb / NJ) dB= (PG) dB – (PJ / PS ) dB

If the interference in the CDMA system is considered as Gaussian in nature, then we can treat NJ as the Gaussian noise spectral density N0.

Then we write an approximate expression for the error probability as: Pe = 1 / 2 * e – (E

b / N0)

From the above we can calculate the required Eb / N0 for a given bit

error rate requirement and vice versa. Some examples are given below:

For Pe = 10-3 Eb / N0 = 7.93 dB = 10-4 = 9.30 dB = 10-5 = 10.34 dB


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Basic Model of Anti Jamming System

Transmitter

Jammer

Bit Rate = Rb

WSS

(WSS / Rb) Eb / NJ = (PJ / PS) WSS

Where, _____ = Processing Gain (P Rb The above could be expressed in dBs as (Eb / NJ) dB= (PG) dB – (PJ / PS ) dB

When the interfering signals appear as wto NO, the basic Gaussian noise spectral

The error performance of the system dep error probability is approximately given by Pe = 1 / 2 * e – (E

b / N0)

© MOTOROLA LTD.2003 CDMA02: Principles of FOR TRAINING PURPOSE South Asia Network Solutio Bangalore, India

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Receiver
PJ

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Follows:

hite noise, we can approximate NJ density. ends on the Eb / NO and the :

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Features of CDMA

_________________________________________________________ High Capacity

CDMA offers more channels per carrier as compared to 8 in GSM. In terms of Erlang traffic offered for any grade of service, CDMA provides roughly ten to twenty times more traffic handling capacity compared to FDMA. Compared to TDMA system, CDMA offers five to seven times more capacity. The increased capacity is also related to the fact that in CDMA, frequency planning is simpler (because all mobiles within a cell transmit at the same frequency). In CDMA, the efficiency of frequency re-use is determined by the total signal – to – interference ratio resulting from ALL the users within range unlike in TDMA systems where the performance and capacity are limited by “worst case” values.

Lower Transmit powers

The reduction in required Eb / NO means that the MS has to transmit less power. This means that the cost of the MS comes down and the batter life increases. This also results in minimum interference; which means more users can talk simultaneously. Hence more capacity.

Improved Privacy

The PN sequence operation, wide band signalling and certain addressee specific protection features provide very good security to the users.

Improved Capabilities

The variable rate vocoders allow multiple levels of grade of service. Interfaces to different data services, ISDN, PBXs including wireless PBXs and cordless/PCN and cellular systems are possible through a common instrument. CDMA could also be used in the local loop of the PSTN, there by making the boundary between fixed and mobile networks virtually seamless.

Better Performance in Fading/Interference Prone Environment

This is derived from the basic concept of spread spectrum technique which separates signals based on specific PN sequences. The system has inherent “multi path diversity” features.


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FEATURES OF CDMA: 1. HIGH CAPACITY

a. More Channels per carrier as against 8 in GSM b. Better traffic handling capacity c. Use of Vocoders increases capacity d. Simpler frequency planning / frequency re-use.

2. Lower transmit powers for the handsets. 2. Improved security 3. Improved Capabilities

a. Variable rate vocoders for different grades of service. b. Interfaces to ISDN/ Wireless PBXs/ PCN/ Cellular c. Local loop applications in the PSTN

5. Better performance in Fading/ Interference prone environment. 6. Ease of Frequency Planning:


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CDMA Standards - Introduction

_________________________________________________________ cdmaOne

CDMA is a relatively recent technology. The first CDMA standard IS-95 was published by TIA in 1993. CDMA systems based on the IS-95 standard and related specifications are referred to as cdmaOne systems. The cdmaOne is intended to represent the end-to-end wireless systems and all of the necessary specifications. The cdmaOne provides a family of related services including cellular, PCS, fixed wireless (wireless local loop) and satellite communications.

IS-95 and IS-95A

IS-95 is first CDMA protocol hence it is called Protocol Revision 1. IS-95A is published in 1995 and is referred to as Protocol Revision 2. IS-95A enables any mobile station to obtain service in any cellular system manufactured according to this standard. IS-95A describes the generation of the channels, power control, call processing, handoffs and registration techniques for cellular system operation. IS-95A does not address quality or reliability of the system.

IS-95A and TSB-74

An additional specification, TSB-74, has been published that describes interaction between an IS-95A system and PCS CDMA systems that conform to ANSI J-STD-008. Systems that implement both IS-95A and TSB-74 are referred to as Protocol Revision 3 systems.

ANSI J-STD-008

Defines compatibility standard for 1.8 to 2.0 GHz CDMA PCS systems. It was published in 1995. It is same as IS-95A. Improvements in signalling and the inclusion of Rate Set 2 frame formats are some of the variances from the IS-95A specification. It does not address the quality or reliability of the service.

TIA/EIA 95

TR 45.5 released IS-95B as its next evolution of CDMA. The standard was released as TIA/EIA 95. This new revision combined IS-95A, TSB-74 and ANSI J-STD-008 into a single specification and eliminate much of redundancy between the three documentation. Analog information was deleted and the standard will refer to existing analog standard IS-553A when applicable. TIA/EIA-95 is protocol revision 4.


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CDMA Standards IS – 95A

• MS – BTS compatibility standard for dual-mode wideband spread spectrum cellular system.

• Provides requirements for MS & BS – analog and CDMA • Provides requirements for base station analog options • Message encryption and voice privacy techniques are defined • CDMA call flow, system layering, retrievable and settable parameters etc.

description • Mobile station database

ANSI J – STD – 008

• Personal Station – Base station compatibility requirements for 1.8 to 2.0 GHz CDMA PCS

• Defines requirements for PCS operation and BS CDMA operation • Message encryption and voice privacy • CDMA call flow, protocol layering, retrieve and settable parameters etc.

description • Personal Station database

TIA/EIA – 95

• It is combination of IS-95A, TSB-74 and J-STD-008. • Analog information is deleted from the standard • Some corrections are made and new capabilities are added


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Frequency re-use

_________________________________________________________ Frequency re-use

The idea of frequency re-use in cellular systems underlined the need for accepting a controlled amount of interference in order to achieve higher system capacities. In order to get more capacity, we need more frequencies. Theoretically, infinite capacity is possible by reducing the cell sizes and increasing the rate of frequency re-use. However, a practical limit is reached when the number of inter cell handovers required increases rapidly.

In GSM

For example in GSM we can have a maximum of 8 users operating at the same frequency. If we want to increase this to say 30 users, then we need 4 frequencies. To minimize interference between users in adjoining cells, we have to choose the operating frequencies carefully. This is done by what is called a Frequency Reuse Plan. Suppose an operator is assigned 27 frequencies. If we choose a 3 sector, 3 cell reuse pattern, then we get 9 frequencies per cell and a maximum of 3 frequencies per sector. As the network grows, the frequency planning in GSM (or any mobile network) becomes more and more complex. The addition of a frequency in any cell or sector has an impact on the usage of frequencies in other cells.

In CDMA

Relatively, this is very simple in CDMA. All sectors and cells in a CDMA network can have the same frequency assignment. This is because, the signals are separated by specific PN sequences, the following statements hold good. This is called Universal Frequency Reuse.

• Interference in CDMA is “pooled” • All users more or less experience the same level of

interference from other users • Roughly 60% of the interference is from users in the same cell • Frequency planning from the re-use point of view is not

needed • Capacity and coverage aspects become more critical than the

frequency planning aspects

This is illustrated in the opposite page.


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A F

E D

C B

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A F

E D

C B

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A F

E D

C B

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A F

E D

C B

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a. Frequency Re-use in GSM

A A

A A

A A

A

A A

A A

A A

A

A A

A A

A A

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A A

A A

A

b. Frequency Re-use in CDMA


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Capacity of CDMA Systems

_________________________________________________________ Capacity of CDMA Systems

The primary measure of performance in digital systems is the ratio of bit energy Eb to noise density NO. Analog signals are power signals, where as the digital signals are energy signals. The capacity of CDMA depends on the Eb / NO and the frequency re-use.

(PS / R) (Eb / NO) = __________ = (W/R) * (PS / PN) (PN / W) Where, PS = Signal Power PN = Noise Power W = Bandwidth of the system R = Bit rate (bits per second) (W/R) is referred to as processing gain

Eb / NO and Capacity

If there are M users and C is the carrier power of any user, then Interference power I could be thought of as equal to C X (M-1). Then the Carrier – to – Interference ratio becomes equal to 1/(M-1).

The relationship between the capacity (number of users), the processing gain PG and the required Eb / NO is given by the simple equation:

M-1 = [PG] / [Eb / NO] If M is large, we can say that M = [PG] / [Eb / NO]

In addition, if we take into account the voice activity factor (v), frequency re-use advantage (f) and sectorization advantage (s), the capacity equation for cell site gets modified as:

M = [PG] * [Eb / NO]-1 * (1/v) * f * s If Rb = 9600 bps, Rc = 1.2288 Mcps, v = 40%, f = 0.65 and s = 2.55 We get the capacity as 107 traffic channels for a 3 sector site.

If we calculate for one sector or an omni site, the capacity becomes 42 channels.


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Capacity of CDMA systems

• The capacity of CDMA systems depends on o Eb / NO o Frequency re – use o Voice activity factor o Sectorization

• For M users we have the basic capacity equation as:

M-1 = [PG] / [Eb / NO]

Where PG is the processing gain WSS / Rb

• Considering voice activity factor (v), frequency re-use advantage (f) and the sectorization advantage (s), the capacity equation gets modified as:

M = [PG] * [Eb / NO]-1 * (1/v) * f * s

• Example: o If Rb = 9600 bps, Rc = 1.2288 Mcps, v= 40%, f = 0.65, and s

= 2.55, We get the capacity as 107 traffic channels for a 3

sector site If we calculate for one sector or an omni site, the

capacity becomes 42 channels


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Applications of Spread Spectrum Systems

_________________________________________________________ Indoor Applications

Wireless LANs Spread Spectrum Cordless telephones, linked to wireless

PBXs Point – of – sale applications such as cash registers, bar –

code readers etc. Building alarm systems

Outdoor Applications

Wireless packet switched networks (bridge/router functions)

for Metropolitan Area Networks (MANs) Campus linking of wired/cabled LANs in different buildings

such as a University or a big manufacturing plant or office or company

In the access network of PSTN, especially in areas where copper costs are quite high and pockets where the subscriber density is less (such as the rural areas)

In high density areas or areas having a high growth rate, the CDMA local loop is more cost effective than the copper based access network


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Applications of Spread Spectrum Systems Indoor Applications

Wireless LANs Spread Spectrum Cordless telephones, linked to

wireless PBXs Point – of – sale applications such as cash registers,

bar – code readers etc. Building alarm systems

Outdoor Applications

Wireless packet switched networks (bridge/router functions) for Metropolitan Area Networks (MANs)

Campus linking of wired/cabled LANs in different buildings such as a University or a big manufacturing plant or office or company

In the access network of PSTN, especially in areas where copper costs are quite high and pockets where the subscriber density is less (such as the rural areas)

In high density areas or areas having a high growth rate, the CDMA local loop is more cost effective than the copper based access network


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SECTION 2

PRINCIPLES OF CDMA


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Section 2 Principles of CDMA 27 Objectives 29 Frequency Spectra of Rectangular Pulses 30 Basics of Spreading Codes 32 Spreading,De-Spreading, Channelization and Recovery 34 The process of Spreading Spectrum 38 Models of Spread Spectrum CDMA Systems 40 One user-One path model of CDMA Systems 40 One user-Many Path model of CDMA System 42 Many Users-Multi path model of CDMA system 46 PN Sequence Generation 48


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Objectives

_________________________________________________________

Objectives

At the end of this section, the trainee is expected to be able to:

Explain the general spreading and despreading processes in CDMA List and explain the basic models of Spread spectrum CDMA Explain the principle of generating PN sequences, with the help of

suitable diagrams. Illustrate with suitable examples, the properties of PN sequences.


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Frequency Spectra of Rectangular Pulses

_________________________________________________________ Frequency Spectra of Rectangular Pulses

Since CDMA is based on spreading the spectrum of the base band signal, let us have a look at the pulse spectra.

Spectrum of a Single Pulse

From Fourier analysis, we know that a rectangular pulse could be considered as a combination of a number of frequency components. The frequency spectrum of a pulse of duration (width) Tb is shown in Fig (a) in the opposite page. The spectrum is mathematically defined by a [(Sin θ)/ θ] function. This is also called a “ Sinc” function or a “ sampling ” function. The spectrum has a number of ‘ null’ points at frequencies given by 1/Tb, 2/ Tb, and so on.

Remember that the spectrum in Fig (a) is for a single rectangular pulse. It is a CONTINUOUS spectrum without any discrete components.

Spectrum of a Pulse Train

Fig (b) gives the spectrum for a periodical pulse train. The pulse width is Tb, and the pulse chain periodicity is T.

The spectrum still has the Sinc function distribution. The nulls are at the same frequency points as mentioned for the single pulse in Fig (a). But, here we get additional components (called power density components) at regular intervals separated by 1/ T.

It can be seen that the width of the spectrum is a function of the Pulse width Tb. If Tb is made smaller, 1/ Tb becomes larger and accordingly the null points in the spectrum gets spread out.

As the period T of the pulse train is increased, 1/T becomes smaller and the spectrum becomes denser. By corollary, if the period T is reduced, then 1/T becomes larger and the additional spectral components get spaced far apart and hence the spectrum becomes less dense.

Reduction of Tb and T means increasing the over all bit rate of the data. This means the integrity/ semantics of the data is altered.


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Spectra of Rectangular Pulses:

1/ Tb-2/ Tb -1/ Tb 2/ Tb 3/ Tb 4/ Tb-3/ Tb-4/ Tb

t

Fig. (a) Spectrum of a Rectangular Pulse

Tb

Tb

T

1/ Tb-2/ Tb -1/ Tb 2/ Tb 3/ Tb 4/ Tb-3/ Tb-4/ Tb

Fig. (b) Spectrum of a Rectangular Pulse Train

1/ T


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Basics of Spreading Codes

_________________________________________________________ Basics of Spreading Codes

There are two types of code sequences used in cdmaOne systems. These sequences are known as Orthogonal sequences (Walsh Codes) and Pseudorandom Noise (PN) sequences.

Orthogonal Sequences

Orthogonal signals have zero-correlation. Zero correlation is obtained if the product of two signals, summed over a period of time, is zero. When the XORing of two binary sequences results in an equal number of 1’s and 0’s, the cross correlation is zero.

Generation of Orthogonal Codes

Orthogonal codes are generated by starting with a seed of 0, repeating the 0 horizontally and vertically, and then complementing the 0 diagonally. This process is to be continued with the newly-generated block until the desired codes with proper length are generated. Sequences created in this way are referred to as “Walsh” codes. The orthogonal sequences used in cdmaOne systems are Walsh codes of length 64. Walsh codes are used in the forward CDMA link to separate users. In any given sector, each forward code channel is assigned a distinct Walsh code.

Pseudorandom Noise (PN) Sequences

PN codes mimic randomness properties. If the current state and the generating function of the PN code is known, the Future state of the code can be predicted. In cdmaOne system each base stations and all mobile in that base station use same set of three PN sequences (two short codes and one long code). PN code generation is dealt in detail later in this section.


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Basics of Spreading Codes Types of code sequences

Orthogonal Sequences (Walsh Codes) Pseudorandom Noise Sequences (PN Codes)

Orthogonal Codes

Orthogonal functions have zero correlation Two binary sequences are orthogonal if the process of “XORing” them

results in an equal number of 1’s and 0’s Example:

0000 0101 ------- 0101 -------

PN Codes

Two short codes (215 = 32,768) o Two codes - “I” and “Q” codes o Unique offsets serve as identifiers for a cell or a sector o Repeat every 26.67 msec at a clock rate of 1.2288 Mcps

One Long Code (242 = 4400 billion) o Used for spreading and scrambling o Repeats every 41 days at a clock rate of 2.1188 Mcps


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Spreading, De-Spreading, Channelization and Recovery

_________________________________________________________ Orthogonal Spreading and De-Spreading

The principle behind spreading and de-spreading is that when a symbol is XORed with a known pattern and the result is again XORed with the same pattern, the original symbol is recovered. Hence, the effect of XOR operation if performed twice using the same code is null. In orthogonal spreading, each encoded symbol is XORed with 64 chips of the Walsh code.

Channalization using Orthogonal Spreading

By spreading, each symbol is XORed with all the chips in the orthogonal sequence (Walsh sequence) assigned to the user. The resulting sequence is processed and is then transmitted over the physical channel along with other spread symbols.

Recovery of Spread Symbols

The receiver de-spreads the chips by using the same Walsh code used at the transmitter. Under no noise conditions, the symbols or digits are completely recovered without any error. But, the channel is not noise free. So, cdmaOne systems employ FEC techniques to combat effects of noise and enhance the performance of the system. When the wrong Walsh sequence is used for dispreading, the resulting correlation yields an average of zero. This is a clear demonstration of the advantage of the orthogonality property of the Walsh codes. Whether the wrong code is by receiver or other users attempting to decode the received signal, the resulting correlation is always zero.


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Orthogonal Spreading 1 ⊕ 0110011010011001100110010110011010011001011001100110011010011001 = 1001100101100110011001101001100101100110100110011001100101100110 Channelization using Orthogonal Spreading User Data 1 0 0 1 1 Orthogonal sequence 0110 0110 0110 0110 0110 TX Data 1001 0110 0110 1001 1001 Recovery of Spread Symbols RX Data 1001 0110 0110 1001 1001 Correct Function 0110 0110 0110 0110 0110 1111 0000 0000 1111 1111 Recovered Data 1 0 0 1 1 Recovery of Spread Symbols using wrong function RX Data 1001 0110 0110 1001 1001 Incorrect Function 0101 0101 0101 0101 0101 1100 0011 0011 1100 1100 Recovered Data ? ? ? ? ?


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Spreading, De-Spreading, Channelization and Recovery

_________________________________________________________ Spreading Example

Three users A,B and C are assigned three orthogonal codes for spreading purposes

• User A Signal = 00, Spreading Code = 0101 • User B Signal = 10, Spreading Code = 0011 • User C Signal = 11, Spreading Code = 0000

The composite signal when all of the spread symbols are summed together is shown on the opposite page

Despreading Example

At the receiver of user A, the composite analog signal is multiplied by the Walsh code corresponding to user A, and the result is then averaged over the symbol time. This process is called correlation. Note the average voltage value over one symbol time is equal to 1. therefore the original bit transmitted by A was “0”. You may try to decode the symbols for users B or C in the same manner. This process occurs in the CDMA mobile unit for recovering the signals.


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Spreading and Despreading Example Spread Waform Representation of User A's Signal

<-------------- Symbol Period----------------------->

1 t

-1 Spread Waform Representation of User B's Signal

1 t -1

Spread Waform Representation of User C's Signal

1 t -1

Analog signal formed by the summation of three spread signals (The same signal is received by all three users)

1 t -1 -2 -3

Walsh Code for User A: "0101"

1 t -1

Product

3 2 1 t

-1 Average = (5-1)/4 = 1 Average = (5-1)/4 = 1 => 0 => 0


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The Process of Spreading the Spectrum _______________________________________________________ The Process of Spreading the Spectrum

Since we cannot alter the bit rate of the signal, we use another pulse train or a code sequence of duration Tc which is a fraction of Tb.

i.e., Tc = Tb/ N

or, Rc = N x Rb

The code is used to chop the data into a number of chips, each chip having a duration of Tc.

The ratio Rc/Rb is called the “ Processing Gain ”.

Let us illustrate the spreading and despreading process through a simple example, as illustrated in the diagram opposite.

Let the base band be : 1 1 0 1.

We chop each bit of the data into 4 bits with a PN sequence. The PN sequence is 4 times faster than the base band data.

The PN sequence for this example is: 1001 0110 1101 0111

The chipping is done by Exclusive-ORing the data with the PN sequence and the data is recovered at the receiver by passing the incoming data and the local PN sequence through an Ex-OR circuitry.

Thus we have:

Base band signal ............... 1 1 0 1 PN Sequence...................... 1001 0110 1101 0111 Transmitted Signal............. 0110 1001 1101 1000

Received Signal................. 0110 1001 1101 1000 Local PN code.................... 1001 0110 1101 0111 Ex-OR output.................... 1111 1111 0000 1111 Integrated over 4 bits...... 1 1 0 1 We get the base band.

The foregoing assumes there is no Propagation delay.


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a. Input base band signal

b. A 4 chip PN sequencr

c. Tx. output- a Ex-OR bd. Rx. input

e. PN sequence at Rx end.

f. Despread or recovered base band signal.

SPREAD SPECTRUM PROCESS - AN ILLUSTRATION


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MODELS OF SPREAD SPECTRUM- CDMA SYSTEMS

_________________________________________________________ MODELS OF SPREAD SPECTRUM- CDMA SYSTEMS

There are basically 4 models of SS-CDMA systems:

One user- One path One user- Many paths Many users- One path Many Users- Many paths

ONE USER- ONE PATH MODEL

With reference to the diagram in the opposite page, the following may be noted:

The base band signal of a user “j” is denoted by........ Bj(t) The PN sequence used for spreading the spectrum is.... Cj(t) The transmitted spectrum for user “j” is......... ............ Bj(t). Cj(t) At the receiver, the signal is received after a delay Tj.Bj(t-Tj). Cj(t-

Tj) We generate the PN sequence locally, with an arbitrary delay:

Cj(t-T) The receiver output is then described by:[ Bj(t-Tj). Cj(t-Tj) ].Cj(t-T) If the local delay T is equal to the propagation delay Tj , then the

receiver output becomes: [ Bj(t-Tj). Cj(t-Tj) ].Cj(t-Tj) = Bj(t-Tj) i.e., at the receiver output we get back the base band delayed by Tj

If the delay T generated locally at the receiver is not equal to Tj then the receiver output becomes: [ Bj(t-Tj). Cj(t-Tj) ] . Cj(t-T) = Bj(t-Tj).Cj(t-Tq). This means that the receiver output is still a “SPREAD” data.

Thus, all other signals arriving at the receiver appear as spread data, excepting the desired data which gets decoded as Bj(t-Tj). The other signals appear as noise.

The foregoing assumes that there is only one direct path between the transmitter and the receiver and the effects of multipath are not considered here.


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ONE USER - ONE PATH MODEL OF CDMA SYSTEM.

Bj (t)

Cj (t)

Bj (t).Cj (t)

Bj (t-Tj). Cj (t-Tj)

Cj (t-T)Bj (t-Tj)

The transmitted signal is a spread spectrumsignal and is given by:

Bj ( t ) . Cj ( t )

Cj is the PN sequence employed by the user # j.

The signal arives at the receiver after apropagation dealy Tj .

The PN sequence Cj is generated locallyat the receiver and used to demodulatethe input signal.Receiver output isgiven by:[Bj (t-Tj) . Cj (t-Tj) ]. Cj (t-T)If T = Tj , then the receiver output isBj ( t-Tj ), which is a delayed base band.


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ONE USER- MANY PATH MODEL OF CDMA SYSTEM

_________________________________________________________ ONE USER- MANY PATH MODEL OF CDMA SYSTEM

The single user-single path model helps us understand the concept of spreading and de-spreading assumes ideal propagation conditions.

In reality, the signal arrives at the receiver through a number of paths, generated by reflections/ scattering from buildings, trees, mountains, water etc.

Therefore, the input to the receiver always has 2 components:

a. A direct path component given by: Bj( t-Tj). Cj(t-Tj) b. A multipath component given by: Bj ( t-Tjm ) . Cj( t-Tjm ),

where Tjm is the multipath delay for the signal from user #j.

Suppose the locally generated PN sequence ( at the receiver ) is delayed by Tj ( meaning that the direct path signal component is synchronized by the receiver ). Let us look at the receiver now:

Receiver input: Bj ( t-Tjm ) . Cj ( t-Tjm ) Locally generated PN code: cj( t-Tj ) Receiver output: Direct path component + Multipath Component

= [Bj( t-Tj). Cj(t-Tj) + Bj ( t-Tjm ) . Cj( t-Tjm )] . Cj ( t-Tj ) = Bj ( t-Tj ) + [ Bj ( t-Tjm ) . Cj( t-Tjm ) . Cj ( t-Tj ) ] ..(A)

The term inside the bracket is the interference signal appearing as a spread multipath signal.

The spread interference or the multipath signal has a (t-Tjm) component . If ( t-Tjm) is LESS than one chip ( one bit ) duration of Cj , the multipath component cannot be resolved and the demodulated output is distorted.


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Multi pathBj(t-Tjm). Cj (t-Tjm)

Direct PathBj (t-Tj). Cj(t-Tj)

Rx

Cj ( t-Tj )LocallygeneratedPN sequence

( t-Tjm ) less than one chip

Interference

Direct path:Bj(t-Tj )

Direct path:Bj(t-Tj )

spreadmutipath

( t-Tjm ) more than one chip

One User- Many Path Model of CDMA System


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ONE USER - MANY PATH MODEL OF CDMA SYSTEM

_________________________________________________________ ONE USER - MANY PATH MODEL OF CDMA SYSTEM ( contd...)

We saw earlier that the received signal has a (t-Tjm) component and that if it is LESS than one chip duration, then it cannot be resolved or rejected. The demodulated signal, as said earlier, appears as a spread interference signal.

However, if ( t-Tjm ) is GREATER than one chip period then it could be resolved. This could be done by introducing a second receiver which has its local PN generator delayed by Tjm. i.e., the second receiver is synchronized with the multipath component. One of the most popular type of such receivers is called the RAKE receiver.

RAKE receiver

The Rake receiver was developed in the late 1950s in the MIT and was patented in 1961. The Rake receiver is a set of four or more receivers. One of the receivers constantly searches for different multipaths and helps to direct the other fingers to lock onto strong multipath signals. Each finger then demodulates the signal corresponding to a strong multipath. The results are then combined together to make the signal stronger. Basically, the receiver has separate local sources for MARK and SPACE, with their outputs connected to delay lines. The delay lines have several tappings. The incoming signal is compared with the MARK and SPACE signal appearing at the tappings and the output is combined , integrated and passed through a decision making circuitry. By this method the MARKS and SPACES are CORRELATED with the incoming signal arriving via different paths and the local sequence generator gets delay properly adjusted. A simplified representation of the Rake receiver is shown opposite. Here, the received signal separated into 2 components:

A direct path component WITH a spread multipath component A multipath component WITH a spread direct path component.

Output of Rx 1 is given by: Bj( t-Tj) + [Bj (t-Tjm).Cj (t-Tjm) Cj(t-Tj) ] ..(A)

Output of Rx 2 is given by: [Bj( t-Tj) + Bj (t-Tjm) . Cj (t-Tjm) ] . Cj (t-Tjm) : Bj (t-Tjm) +[ Bj( t-Tj) . Cj (t-Tj) . Cj (t-Tjm) ]...........(B)

The terms within bracket in equations A and B represent the spread components associated with the direct and multipath components respectively.


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ONE USER- MANY PATH MODEL OF CDMA SYSTEM.. CONTD..

Multi pathBj(t-Tjm).Cj(t-Tjm)

Direct PathBj(t-Tj).Cj(t-Tj)

Rx1

Rx2

Cj(t-Tj)

Cj(t-Tjm)

Direct Path

SpreadMultipath

Multi path

SpreadDirect Path

RakeReceiver


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MANY USERS - MULTIPATH MODEL OF CDMA SYSTEM

_________________________________________________________ MANY USERS - MULTIPATH MODEL OF CDMA SYSTEM

In a real life situation, there would be many users operating at the same frequency, at the same time. Each user would be spreading the signal with a unique PN sequence.

The signals sent by each user undergo multipath propagation and hence would have direct path and multipath components at the receiver. The desired signal is separated by the receiver by using a local PN sequence generator as explained earlier.

Also, if the time difference (t-Tj) is greater than one chip duration, then for each user, the multipath component could be resolved by using a Rake receiver arrangement.

However, for each user, there would be additional interference signals in the form of signals from other users operating at the same frequency.

Say there are 3 users p , q and r.

Then for user p, the receiver will have:

A direct path component given by: Bp(t-Tp) Spread interference signals pertaining to pq and pr.

Components pq and pr are interfering signals from users q and r received at p. In other words, pq and pr are the CO CHANNEL interference for the desired signal viz., Bp(t-Tp).

This is illustrated in the diagram opposite.


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Bp

Bq

Br

Cp

Cq

Cr

Bp(t-Tp).Cp(t-Tp)

Bq(t-Tq).

Cq(t-T q)

B r(t-T r).

C r(t-T r)

Cp(t-Tp)

Cq(t-Tq)

Cr(t-Tr)

Bp(t-Tp)

pq

pr

MANY USERS - MULTIPATH MODEL OF CDMA SYSTEM


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PN SEQUENCE GENERATION

_________________________________________________________ PN SEQUENCE GENERATION

The most important element in the transmitter and receiver in a CDMA system is the PN sequence generator which is used for spreading and despreading signals.

Definition

A pseudo random sequence is one in which the bits appear in a random manner within a specified sequence length and the pattern is repeated for subsequent sequences. PN sequences have an important property: Times shifted versions of the same PN sequence have very little correlation with each other. The channelization of users in the reverse link is accomplished by assigning them different time shifted versions of the long code, thus making them uncorrelated with each other. This property is then exploited to separate subscriber’s signals in the BTS receivers.

Examples

Suppose we have 4 digit words. The natural sequence is from 0000 to 1111. Purely random sequence could be a series of 15 word sets, with the combination of words in each set being random. Pseudo random sequence would be a series of 15 word sets, with the pattern of words in any set being the same.

The natural sequence makes the signal highly predictable while the pure random sequence makes it totally unpredictable and even the desired signal cannot be recovered.

Hence the PN sequence is the best choice as it appears as noise to all other users excepting the desired receiver.

Requirements of a PN sequence:

The PN sequence should:

be easy to generate have random properties have long periods be difficult to reconstruct from a short segment.


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• The PN sequence is important because, the receiver needs a replica of the transmitted sequence to de spread the signals.

• The PN sequence has a random set of words which repeat after a specific

sequence length.

• A pure sequence is highly predictable and a pure random signal makes it difficult even for the desired receiver to recover the signal. Hence, the PN sequence is the best choice.

Example of a PN sequence: Consider a 4 bit sequence

0001 1000 1100 1110 1111 The sequence repeats itself. 0111 1011 0101 1010 1101 0110 0011 1001 0100 0010

The PN sequence should

1. Be easy to generate 2. Have random properties 3. Have long periods 4. Be difficult TO reconstruct from a short segment.


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_________________________________________________________ Types of PN generators

There are various types of PN generators such as:

1. ROM based generators 2. Cyclic Shift Register Generators 3. Counter based generators 4. Simple Shift Register generators with Linear feedback logic (LF-

SSRG) 5. Fibonacci generators 6. Galois generators 7. Multiple return shift register generators ( MRSRG) 8. Non linear feed forward generators.

We will look at the simple shift register type PN generator with linear feed back arrangement. The diagram opposite gives the generic configuration which could be modified to give specific PN sequences. The generator has a number of shift registers in cascade with tappings at various points; the tapped outputs are passed through modulo-2 adders (Exclusive - OR) and the output is fed back to the first stage.

For a given shift register length, the feedback connections determine whether the output sequence length is maximal or not. It is also not possible to generate maximal length sequences from an SSRG with odd number of taps. For a shift register generator with ‘n’ stages, the maximal sequence length is given by:

L = 2n-1 PN Offset (Masking)

Masking provides the shift in time for PN codes. Different masks correspond to different time shifts. In cdmaOne systems, Electronic Serial Numbers (ESN) are used as masks for used on the traffic code channels. Masking is used to produce offsets in both the short codes and the long code. The offsets of the short PN codes are used to uniquely identify the forward channels of individual sectors or cells. The offsets of the Long code are used to separate code channels in the reverse direction.


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1 2 3 4 5 6 7 .. ..... n

feedback logic- exclusive OR circuits

outputsequence.

A Generic Form of a Simple Shift Register Generator.


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_________________________________________________________ PN SEQUENCE GENERATION

Consider a 4 stage shift register PN generator with feedback tappings as shown in the diagram. Let the shift register be loaded initially with 0001. Then as per the feedback arrangement, successive clock pulses generate a set of 15 four bit words in a random fashion. The sequence is repeated for successive cycles. The output taken at shift register stage 4 is 100011110101100. This forms the PN code used for spreading/despreading the base band signal. Note that the shift register should not be loaded with all ‘0’s.

If the feedback tappings are changed, say , from stages 2 and 3, then we would get a different PN sequence. You may verify this by assuming the same initial loading of the shift register. Also study the effect of changing the initial loading.

Note that the sequence length gets reduced if we take feedback only from one stage or from 3 stages. ( Odd tappings).

Properties of PN Sequences

PN sequences exhibit the following properties:

The maximal length of the sequence is 2n-1, where n is the number of stages in the shift register. The number of ‘1’s will be 2 (n-1) and that of ‘0’s will be 2(n-1)-1. i.e., the number of ‘1’s will be one more than the number of ‘0’s. If a maximal SRG sequence is added to a phase shift ( time shift )of itself then the resulting sequence is another phase shift of the original sequence. This is called the “shift and add” property of SSRGs.


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+

000110001100111011110111101101011010110101100011100101000010

1 2 3 4

0 0

A 4 Stage SSRG type PN sequence generator

0 1

•The output sequence is : 100011110101100• It is 15 bits long’i.e., L= 2n-1• There are 8 ones and 7 zeros• In any period, half the run of continuous 1s or 0s are of length 1 one fourth run are of length 2, one eighth are of length 3 and so on.• Shift and Add property:If the PN sequence is shifted in time, the resulting sequence is anothershif of the original sequence itself. If the shift is by one bit/chip, then the original pattern repeats after 2n-1 sequences.Example: Origianl Code: 100011110101100 100011110101100 100011110101100 Code shifted in by 1 bit: 000111101011001 000111101011001 000111101011001 Exclusive-OR sum:: 100100011110101 100100011110101 100100011110101The original code is undrlined.By shifting the sequence successively by one bit,it can be verified that the original sequence repeats after 15 sequences (2n-1).

Exercise: For the same tappings, change the initial Seeding of the Shift Register and obtain the output sequence. What are your observations on the new sequence?


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PN SEQUENCE GENERATORS

_________________________________________________________ PN SEQUENCE GENERATORS

The separation of the desired signal from other spread signals is achieved, as said earlier, by means of a locally generated PN sequence which is a replica of the one used at the transmitter; the local PN sequence at the receiver is delayed by an amount equal to the propagation delay in order to synchronize it with the transmitted PN code. All other signals (PN codes) are rejected because of code mismatch. This is possible because the PN sequences exhibit certain AUTO CORRELATION AND CROSS-CORRELATION PROPERTIES.

Auto Correlation

In general, this describes the extent of likeness between a random variable and its time shifted version. It can be defined by a simplified formula:

Auto Correlation = ∫ x(t) * x(t-T) dT For PN sequences this could be written as:

Tb Auto correlation = ∫ Cj(t) * Cj(t-T) dT 0

The Auto correlation function of the PN sequence has a positive value = 2n-1 for zero time shift instances and has a small negative value at other instances, when the shift in time is equal to or more than one chip duration.

Cross-Correlation Function

Cross-correlation defines the likeness between TWO DIFFERENT random variables and could be described by:

Cross Correlation: ∫ x(t) * y(t-T) dT.

For a PN sequence, this could be re written as: Tb Cross correlation = ∫ Cj(t) * Ck(t-T) dT 0

The cross correlation function will have very small negative values.

For our original sequence 100011110101100, the auto correlation value is 15 and its value at instances other than T0 is -1.


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Auto Correlation for PN Sequences Tb Auto correlation = ∫ Cj(t) * Cj(t-T) dT 0 Cross Correlation for PN Sequences Tb Cross correlation = ∫ Cj(t) * Ck(t-T) dT 0


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_________________________________________________________ AUTO CORRELATION AND CROSS-CORRELATION OF PN SEQUENCES

Auto Correlation describes the similarity between a PN sequences and its own time shifted sequence.

Cross correlation defines the similarity between two different random (PN) sequences.

Example of Auto Correlation

Consider the original sequence 100011110101100. This is compared with receive sequences with time shifts T0, T1, T2 etc. T0 means zero time shift or exact synchronization between trans. and receive sequences. To calculate the auto correlation values, we give a mark of +1 for every bit that matches with the reference ( original) sequence and -1 for every bit mismatch. The summary is given below with a graphical representation.

Reference Code: 1 0 0 01 1 1 1 0 1 0 1 1 0 0 autocorrelation Time shift 0: 1 0 0 0 1 1 1 1 0 1 0 1 1 0 0 15 Time shift 1: 0 0 0 1 1 1 1 0 1 0 1 1 0 0 1 -1 Time shift 2: 0 0 1 1 1 1 0 1 0 1 1 0 0 1 0 -1 Time shift 3: 0 1 1 1 1 0 1 0 1 1 0 0 1 0 0 -1 and so on.


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0 1 2 3 4 5 6 7 8 9 1 0

t

AutoCorrelationvalue

1 1

1 2

1 3

1 4

0

15

- 1


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_________________________________________________________ Cross- Correlation of PN sequences

If we change the feed back tappings for our 4 stage SSRG, we get an entirely different PN sequence. Let us take the fed back from the 3rd and 4th stage outputs with the initial loading as 0001, from left to right.

The new PN sequence is: 100010011010111

We take a timeshifted code from the original sequence 100011110101100 and compare that with the new code generated as explained above. This would give us the cross correlation values between the 2 different PN sequences. It is also possible to have the comparison between the first code and a time shifted version of the second.

Note that the cross correlation values vary from -5 to +7, depending upon the extent of similarity between the 2 sequences. The comparison between the 2 PN sequences is given below and the cross correlation function is presented pictorially in the opposite page.

Reference Code 1 0 0 0 1 0 0 1 1 0 1 0 1 1 1 Cross correlation 2nd Code,Time Shift 0: 1 0 0 0 1 1 1 1 0 1 0 1 1 0 0 -1 Time Shift 1: 0 0 0 1 1 1 1 0 1 0 1 1 0 0 1 -1 Time Shift 2: 0 0 1 1 1 1 0 1 0 1 1 0 0 1 0 -1 Time Shift 3: 0 1 1 1 1 0 1 0 1 1 0 0 1 0 0 -5 Time Shift 4: 1 1 1 1 0 1 0 1 1 0 0 1 0 0 0 -5 Time Shift 5: 1 1 1 0 1 0 1 1 0 0 1 0 0 0 1 +1 Time Shift 6: 1 1 0 1 0 1 1 0 0 1 0 0 0 1 1 -5 Time shift 7: 1 0 1 0 1 1 0 0 1 0 0 0 1 1 1 +2 Time Shift 8: 0 1 0 1 1 0 0 1 0 0 0 1 1 1 1 +1 Time Shift 9: 1 0 1 1 0 0 1 0 0 0 1 1 1 1 0 -1 Time Shift 10: 0 1 1 0 0 1 0 0 0 1 1 1 1 0 1 -5 Time Shift 11: 1 1 0 0 1 0 0 0 1 1 1 1 0 1 0 +1 Time Shift 12: 1 0 0 1 0 0 0 1 1 1 1 0 1 0 1 +7 Time Shift 13: 0 0 1 0 0 0 1 1 1 1 0 1 0 1 1 -1 Time Shift 14: 0 1 0 0 0 1 1 1 1 0 1 0 1 1 0 -1 ------------------------------------------------------------------------------------------- Time shift 0: 1 0 0 0 1 1 1 1 0 1 0 1 1 0 0 -1

You may compute the cross correlation value between the first code and the time shifted sequences of the second code, as an exercise.


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Cross-Correlation between PN sequences By taking feed back taps from different points in the 4 stage SSRG, we can get a different PN sequence.

1 2 3 4

0 0 0 1

+

000110000100001010011100011010110101101011011110111101110011--------0001

output sequence: 1000 1001 1010 111.

Fig.(a). Alternate configuration of the 4 Stage SSRG.

876543

210

-1-2-3-4

-5-6

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0 1 2 3 4

Fig.(b) Cross correlation between 2 PN sequences.


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Section 3

IS-95 Concepts


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Section 3 IS-95 Concepts 60 Objectives 62 Introduction to IS-95 63 CDMA Standards 65 CDMA Channels 69


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Objectives

_________________________________________________________ Objectives


Specify CDMA Channel frequency Assignments List the major terminologies such as Forward Link, Reverse Link etc.

.


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Introduction to IS-95

_________________________________________________________ Introduction to IS-95

As the AMPS mobile network in the US reached its capacity limits, mainly in terms of frequency reuse, a strong need for a uniform standard that would make all the existing analog and digital subscribers to coexist and also provide scope for increased capacity was felt. This resulted in the formulation of: “MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL MODE WIDE BAND SPREAD SPECTRUM CELLULAR SYSTEMS”.

This has been accepted as an Interim Standard (hence the name IS-95) by the TIA and EIA of USA. The standard ensures that an MS can get service from any cellular system produced based on this standard. The standard also contains provisions for future service additions and expansion of system capabilities without any loss of backward compatibility to older mobiles. IS-95 is a vehicle for standardization between MS and base station vendors. It defines modulation, coding, error detection & correction, message structure and call processing.The standards are also augmented vocoder service options (IS-96) and data & FAX options (IS-99).

Basic Terminology Forward Link: Base Station to the Subscriber Reverse Link: Subscriber to the Base station CDMA channel: One CDMA RF pair of frequencies separated by

45 MHz and of 1.25 MHz bandwidth each. . Code Channel: The orthogonal communication channel (logical

channels) carried by the forward link (defined by what are known as Walsh Codes).

Code Symbol: The output of the encoder. Walsh Codes: A set of 64 bit orthogonal codes used for

modulating the input data. Each code is called a modulation symbol. On the reverse channel, one modulation symbol is used for 6 code symbols. ON the forward channel, one modulation symbol is used for one code symbol.

Chip: The output digits of a spreading code generator are commonly termed as chips. A chip is also a single binary digit. Several chips are used to spread a single code symbol. Chip Rate is a measure of amount of spreading performed. Bits, symbols and chips all look the same: a single binary digit. What distinguishes one from another is their relationship with information signal


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Introduction to IS-95

IS-95 is an Interim Standard developed for providing standardization between Subscriber equipment and base station vendors. It is called the “ Mobile Station-Base station Compatibility standard for

Dual Mode Wide band Spread Spectrum Cellular Systems”. Defines modulation, coding, error detection/correction, message

structure and call processing. Basic Terminology

Forward Link: Base station to Subscriber Reverse Link: Subscriber to Base Station Code Chl. : The orthogonal (logical) channel carried by the forward

link. Code Symbol: The output of the encoder. CDMA chl. : One CDMA pair of frequencies separated by 45 MHz,

of 1.25MHz bandwidth each. Walsh Code:

A set of 64 bit orthogonal codes used for modulating input data. Each code is called a Modulation Symbol. In the reverse channel, for 6 code symbols one modulation symbol is used; for the forward channel, one modulation symbol is used for every code symbol.

Chip: The output digits of a spreading code generator are commonly termed as chips. A chip is also a single binary digit. Several chips are used to spread a single code symbol. Chip Rate is a measure of amount of spreading performed. Bits, symbols and chips all look the same: a single binary digit. What distinguishes one from another is their relationship with information signal


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CDMA Standards

_________________________________________________________ Related Standards

IS-3 The original analog cellular standard, now replaced by ANSI standard EIA/TIA-553 and TIA interim standard IS-91

IS-41 The protocol for roaming within USA, describing how services

should handover between operators

IS-54 The TDMA standard for US digital cellular. A digital cellular system that squeezes three conversations into one cellular channel

IS-88 Narrowband Analog cellular system developed by Motorola

that squeezes three conversations into one cellular channel using analog frequency division multiplexing. First standardized in TIA interim standard IS-88, and now incorporated in IS-91

IS-91 Analog Cellular PCS. The TIA version of the analog cellular

standard, incorporating the functionality of IS-88 (narrowband analog) and IS-94 as well as PCS band operation

IS-94 Inbuilding Cellular. A standard for inbuilding operation of

analog cellular systems using extremely low power. Now incorporated in IS-91.

IS-95A The CDMA standard for U.S digital cellular. A digital cellular

system that squeezes between 10 and 20 conversations into one cellular channel by combining 30 KHz cellular channels into a single 1.25MHz channel and using code division multiplexing to combine and recover the individual conversations.

IS-96A TIA standard for the variable rate vocoder IS-97 TIA minimum performance standard for the CDMA base

station IS-98 TIA minimum performance standard for the CDMA mobile. IS-99 TIA standard for data services option using the variable rate

Vocoder


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Related Standards • IS-96: Speech Service Option for CDMA ( Vocoders) • IS-97: 800 MHz base station • IS-98: 800 MHz mobile station • IS-99: Data and G3 FAX over CDMA • IS-125: Min. Performance Std. for CDMA speech service Option. • IS-127: Enhanced Variable Rate Vocoders ( EVRCs) • IS-126: Mobile Station Loop back for CDMA • IS-637: SMS for CDMA • IS-657: Packet Data over CDMA • IS-683: Over the Air ( OTA ) Service provisioning for CDMA.


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CDMA Standards

_________________________________________________________ Related Standards

IS-136 TIA standard that provides dual mode (analog and digital) cellular services using the TDMA technology. An enhancement to IS-54 TDMA, that includes a more advanced control channel known as Digital Control Channel (DCCH), to distinguish it from the analog control channel, which although less sophicated, still digital

IS-634 TIA standard for 800 MHz cellular base-station to switch

interface. Supports CDMA.

IS-651 TIA standard for an open interface between the PCS switching center and the radio base station subsystem in a PCS network. Supports both GSM and CDMA

JDC Japanese Digital Cellular – now renamed PDC. Uses upper

900 MHz and 1.5 GHz bands

J-TACS Japanese Total access communication system. Narrowband analog cellular FM system used in Japan. Channels are 12.5 KHz wide and signalling is subaudio.

PCN Personal Communication Network. PCNs are usually short

range (100ft to 1 mile or so) and involve cellular radio type architecture. Services include digital voice, FAX, mobile data and national/international data communications. Also a network of pocket size radio telephones served by clusters or receiver transmitter cells.

PCS Personal Communication Service. Within US, the 1.9 GHz

band has been allocated for PCS systems; the allocated spectrum is 120 MHz wide and is licensed as two 30 MHz segments for the 51 major trading areas, and three 10 MHz segments for the 493 basic trading areas

PCS-1900 DCS-1900

EIA/TIA-553 The ANSI version of the analog cellular standard. Generally

one step behind IS-91, without support for NAMPS


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Related Standards IS-136 Cellular service using TDMA technology. An enhancement to IS-54 TDMA

IS-634 TIA standard for 800 MHz cellular base-station to switch interface

IS-651 TIA standard for an open interface between the PCS switching

center and radio base station subsystem in a PCS network. Supports both GSM and CDMA

JDC Japanese Digital Cellular. Uses upper 900 MHz and 1.5 GHz

J-TACS Japan Total Access Communication Systems. Narrow band

analog cellular FM system used in Japan.

PCN Personal Communication Network. Short range cellular radio service

PCS Personal Communication Service. 1.9GHz band cellular

services

EIA/TIA-553 The ANSI version of the analog cellular standard. Generally one step behind IS-91, without support for NAMPS


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CDMA Channels

_________________________________________________________ CDMA Channels

The frequency channels for CDMA are derived from the allocations made for the analog AMPS system. The forward and reverse frequencies are 45 MHz apart and have a bandwidth of 1.25 MHz each. In the analog system the channels are numbered from 1 to 1023. The basic systems A and B have 10 MHz band width and account for channel numbers 1 to 666. System A’ with an additional bandwidth of 1.5 MHz accounts for channel extension from 667 to 716; System B’ with 2.5 MHz extends the channel capacity from 717 to 799 and system A’’ accounts for another 33 channels from 991 to 1023.

The table opposite shows the channel frequencies and numbers. The centre frequency of a given channel number is calculated as shown below:

CDMA channel number to Channel frequency Assignment Transmitter CDMA chl Number CDMA channel Freq in MHz. Mobile Station 1 ≤ N ≤ 777

1013 ≤ N ≤ 1023 .030 N + 825.000 .030( N-1023)+825.000

Base Station 1 ≤ N ≤ 777 1013 ≤ N ≤ 1023

.030 N + 870.000

.030(N-1023)+870.000

We now define Primary and Secondary CDMA channels.

These are pre assigned CDMA channels used by the mobiles for initial acquisition purposes. The Primary CDMA channel for System A is Channel Number 283 and 384 for System B. The secondary CDMA channel is channel Number 691 for system A and 777 for System B.

In the table shown opposite, column 3 gives the total number of analog AMPS channels within the specified band. Column 4 gives the end to end analog channel numbers for the given band.

For example, if we choose CDMA band in System A’’, then we get the band from 824.700 to 825.000 MHz. This accounts for 11 analog channels from channel numbers 1013 to 1023. If we choose channel number 1020 as our CDMA channel, then the centre frequency would be as specified in the table above.


Issue II Rev 4

CDMA Channel Numbers and Frequency Assignment System

Valid CDMA Frequency Assignments

Analog Channel Count

Transmitter Frequency

Assignment CDMA channel number

Mobile Base A’’

( 1 MHz )

/ / / / / / / / /

22 991 1012

824.040 824.670

865.040 869.670

CDMA 11 1013 1023

824.700 825.000

869.700 870.000

A

( 10 MHz )

CDMA

311

1

283 311

825.030 Primary 834.333

870.030 879.333

/ / / / / / / / / 22 312 333

834.360 834.990

879.360 879.990

B

( 10 MHz )

/ / / / / / / / / 22 334

355

835.020 835.650

880.020 880.650

CDMA 269 356

384 644

835.680 Primary 844.320

880.680 889.320

/ / / / / / / / / 22 645 666

844.350 844.980

889.350 889.980

A’

(1.5 MHz )

/ / / / / / / / / 22 667

688

845.010 845.640

890.010 890.640

CDMA 6 689 691 694

845.670 secondary 845.820

890.640 890.820

/ / / / / / / / / 22 695

716

845.850 846.480

890.850 891.480

B’

( 2.5 MHz )

/ / / / / / / / /

22 717

738

846.510 847.140

891.510 892.140

CDMA 39 739

777

847.170 848.310 secondary

892.170 893.310

/ / / / / / / / / 22 778 799

848.340 848.970

893.340 893.970


Issue II Rev 4

CDMA Frequencies in the 1900 MHz Band

_________________________________________________________ CDMA Frequencies in the 1900 MHz Band

There are 5 blocks of frequencies specified for CDMA applications in the 1900 MHz band as shown in the page opposite.


Issue II Rev 4

CDMA frequencies in the 1900 MHz Band

• There are 5 blocks of frequencies specified for CDMA applications in the 1900 MHz band.

Band Transmit Frequency Band

Designator MS BTS A 1850-1865 1930-1945 D 1865-1870 1945-1950 B 1870-1885 1950-1965 E 1885-1890 1965-1970 F 1890-1895 1970-1975 C 1895-1910 1975-1990

CDMA Carrier Spacings

1.25 MHz

1.23 MHz

This is the minimum carrier spacing. Actual spacing should be an integral multiple of 30 KHz and is also dependent on other design criteria.


Issue II Rev 4


Issue II Rev 4


Issue II Rev 4


Issue II Rev 4


Issue II Rev 4

Section 4

IS-95 CDMA Air Interface


Issue II Rev 4

Section 4 IS-95 CDMA Air Interface 77y Objectives 79 IS-95 CDMA Air Interface 80 Forward Link 82 Paging and Pilot channels 84 System Access 86 Forward Traffic Channel 88 Forward Code Channel and Supplemental Channel 90 Reverse Link 92


Issue II Rev 4

Objectives

_________________________________________________________ Objectives


• Explain IS-95 CDMA air interface • Explain forward link • Explain reverse link


Issue II Rev 4

IS-95 CDMA Air Interface

_________________________________________________________ IS-95 CDMA Air Interface

In US, wireless system operates either in Band Class 0 (850 MHz band) or in Band Class 1 (PCS band-1.8 GHz). IS-95 system operates on the same frequency band as the AMPS. The forward and reverse frequencies are 45 MHz apart and have a bandwidth of 1.25 MHz each. The mobile station supports CDMA operations on AMPS channel numbers 1013 through 1023, 1 through 311, 356 through 644, 689 through 694 and 739 through 777. The CDMA channels are defined in terms of an RF frequency and code sequence. Sixty four Walsh functions are used to identify the forward or down link channels where as 64 long PN codes are used for the identification of the reverse (up) link channels. The modulation and coding features of the IS-95 CDMA system are listed in the page opposite. Modulation and coding details for reverse link and forward link channels differ. The cdma system uses power control and voice activation to minimize mutual interference. Voice activation is provided by using a variable – rate vocoder that operates at a maximum rate of 8kbps to a minimum rate of 1 kbps for Rate Set 1. A coding algorithm at 13.3 kbps for RS2 is also supported. A time interleaver with a 20-ms span is used with error control coding to overcome rapid multipath fading and shadowing. The CDMA radio uses a RAKE receiver to take advantage of a multipath delay greater than 1 µs, which occurs commonly in urban and suburban areas.


Issue II Rev 4

Modulation and coding Features of IS-95 CDMA system

Modulation Quadrature Phase Shift Keying (QPSK) Chip Rate 1.2288 Mcps Nominal Data Rate (RS1) 9600 bps Filtered Bandwidth 1.23 MHz Coding Convolutional with Viterbi decoding Interleaving With 20-ms span


Issue II Rev 4

Forward Link

_________________________________________________________ Forward Link

The forward link channels include one Pilot Channel, one Synchronization (SYNC) Channel, up to seven Paging channels and number of forward Traffic Channels. If multiple carriers are implemented, the pilot and sync channels do not need to be duplicated. Each forward traffic channel contains one forward fundamental code channel and may contain one to seven forward supplemental code channels.

Walsh Codes for Forward Link The information on each channel is modulated by the appropriate Walsh function and then modulated by a quadrature pair of PN sequences at a fixed at a fixed chip rate of 1.2288 Mcps. The pilot channel is always assigned to code channel number 0. If the sync channel is present, it is given the code channel number 32. Whenever paging channels are present, they are assigned the code channel 1 through 7 in sequence. The remaining code channels are used by forward traffic channels.

The Sync Channel

The sync channel operates at a fixed data rate of 1200 bps and is convolutionally encoded to 2400 bps, repeated to 4800 bps, and interleaved over the period of the pilot pseudo random binary sequence. Each of the interleaved symbols uses four Walsh symbols. The Sync channel is used by mobiles to obtain timing and cell specific information. Mobiles must acquire the sync channel to decode its message in order to synchronize with the system. The Sync message includes the following information.

• Pilot PN Offset • System Time • State of the Long PN code • Common air interface revision level • System ID • Network ID • Paging Channel Data Rate

The Sync channel modulation parameters are given in the page opposite.


Issue II Rev 4

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Issue II Rev 4

Forward Link

_________________________________________________________ Paging Channel

Paging channels provide mobile stations with system information and instructions in addition to acknowledging messages following access requests on the mobile station’s access channels. The paging channel is processed in a manner similar to the traffic channel data. There is no variation in the power level on a per-frame basis. The 42 bit mask is used to generate the long code. The paging channel operates at a data rate of 9600 or 4800 bps. A system operator may choose to support less than seven paging channels. In this case, unused codes may be assigned to traffic channels. A paging code channel transmits the configuration messages:

• System Parameters Message • Neighbor List Message • Access Parameters Message • CDMA Channel List Message • Global Service Redirection message

Modulation parameters of paging channel are given in the page opposite

Pilot Channel

Pilot CDMA signal is transmitted by a base station provides a reference for all mobile stations. The pilot signal level for all base stations is about 4 to 6 dB higher than the traffic channel with a constant value. Every cell or sector must transmit a Pilot Code Channel for each frequency is supported. Pilot signals contain no messages. It is used to demodulate traffic channels. Also, thre received power level of pilot signal enables the mobile station to estimate the path loss between base station and the mobile station. Knowing this path loss, the mobile station adjusts its transmitted power such that the base station will receive the signal at the requisite power level. The base station measures the mobile station’s received power and informs the mobile station to make the necessary adjustment to its transmitted power. Once command every 1.25 ms adjusts the transmitted power from the mobile station in + 0.5 steps. The base station uses frame errors reported by mobile station to increase or decrease the transmitted power. CDMA provides soft handoff. As the mobile moves to the edge of cell, the adjacent base station provides resources to the call; mean while the current base station continues to handle the call. The call is handled by both base stations on a make-before-break basis. The pilot signals are quadrature pseudorandom binary sequence signals with a period of 32,768 chips. Since the chip rate is 1.2288 Mcps, the pilot pseudorandom binary corresponds to a period of 26.66. ms which is equivalent to 75 pilot channel code repetitions every 2 seconds.


Issue II Rev 4

Paging Channel Modulation Parameters Parameter Data Rate

9600 bps Data Rate 4800 bps

Units

PN chip rate 1.2288 1.2288 Mcps Code Rate 1/2 1/2 Bits per code

symbol Code symbol repetition

1 2 Modulation symbols per code symbol

Modulation symbol rate

19,200 19,200 Sps

PN chips per modulation symbol

64 64 PN chips per modulation symbol

PN Chips per bit 128 256 PN chips per bit


Issue II Rev 4

Forward Link

_________________________________________________________ System Access

The pilot signals from all base stations use the same pseudorandom binary sequence, but each base station is identified by a unique time offset of its pseudorandom binary sequence. These offsets are in increments of 64 chips, providing 511 unique offsets relative to 0 offset code. A mobile station processes the pilot channel to find the strongest signal components. Once the mobile station identifies the strongest pilot offset, it examines the signal on its sync channel which locked to the pseudorandom binary sequence signal on the pilot channel. Since the sync channel is time aligned with its base station’s pilot channel, the mobile finds the information pertinent to this particular base station on the sync channel. The sync channel message contains time of day and long-code sychronization to ensure that long-code generators at the base station and mobile station are aligned and identical. The mobile station now attempts to access the paging channel and listens for system information. The mobile enters the idle state when it has completed acquisition and synchronization. When informed by the paging channel that voice traffic is available on a particular channel, the mobile station recovers the speech data by applying the inverse of spreading procedures

Basic Forward-Reverse channel Interactions The following steps / interactions apply

• Initial synchronization • Registration • Idle state hand offs • Mobile originated Calls • Mobile terminated calls • Soft Handovers • Authentication..


Issue II Rev 4

Base Station

“Idle State”

•System Acquisition through PILOT channel•Synchronization through SYNC channel•System , Access and Paging Parameters through PAGING channel.•All communications during idle state through Access and Paging Channels only.

Busy State

Use Traffic Channels.


Issue II Rev 4

Forward Link

_________________________________________________________ Forward Traffic Channel

The forward traffic channels are grouped into “Rate Sets”. A Rate Set is a set of traffic channel frame formats. Each set is comprised of 4 bit rates. A rate set may carry voice, user data or signalling. Two Rate Sets are defined for use in cdmaOne systems. All services provided over the air interface must conform to one of these two sets. Rate Set1 (RS 1) has four elements – 9600, 4800, 2400 and 1200 bps. Rate Set 2 (RS2) contains fours elements – 14,400, 7200, 3600 and 1800 bps. When a radio system supports a rate set, it supports all four elements of the set. All radio system supports RS1 on the forward traffic channels. RS2 is optionally supported on the forward traffic channels. Speech is encoded using a variable-rate vocoder to generate forward traffic channel data depending on voice activity. Since, frame duration is fixed at 20 ms, the number of bits per frame according to the traffic rate. Half rate convolutional encoding is used, which doubles the traffic rate give rates from 2400 to 19,200 symbols per second. Interleaving is performed over 20ms. A long code of 242 –1 (=4.4 X 1012) is generated containing the user’s ESN embedded in the MS long code mask. ESN (Electronic Serial Number) is a 32 bit code that is unique to each mobile. Each cellular phone is assigned an ESN, which is automatically transmitted to the base station every time a cellular call is placed. The MTSO checks the ESN to make sure it is valid, that the phone has not been reported stolen, that the user’s monthly bill has been paid etc., before permitting the call to go through. The data is multiplexed with power control information that steals bits from data. The multiplexed signal remains at 19,200 bps and is changed to 1.2288 Mcps by the Walsh code Wi assigned to the ith user traffic channel. The signal is spread at 1.2288 Mcps by pilot quadrature pseudorandom binary sequence signals, and the resulting quadrature signals are then weighted. The power level of the traffic channel depends on its data transmission rate. Traffic channels support user voice, user data other than voice and call control messages. These applications are defined as service options. The following service options are supported

• 8K voice • 8K MS loopback • EVRC (Enhanced Variable Rate Coder) • Async Data (rate set 1) • G3 Fax (Rate Set 1) • SMS (Rate Set1) etc..

Modulation parameters of traffic channel for RS1 and RS2 are given in the page opposite.


Issue II Rev 4

Forward Traffic Channel Modulation Parameters for RS1 Parameters 9600

bps 4800 bps

2400bps 1200 bps

Units

PN chip Rate 1.2288 1.2288 1.2288 1.2288 Mcps Code Rate 1/2 1/2 1/2 1/2 Bits per code


1 2 4 8 Repeated symbols per code symbol

Modulation symbols rate

19,200 19,200 19,200 19,200 Sps


64 64 64 64 PN chips per modulation symbol

PN chips per bit 128 256 512 1024 PN chips per bit Forward Traffic Channel Modulation Parameters for RS2 Parameters 14,400

bps 7200 bps

3600 bps

1800 bps

Units

PN chip Rate 1.2288 1.2288 1.2288 1.2288 Mcps Code Rate 1/2 1/2 1/2 1/2 Bits per code


1 2 4 8 Repeated symbols per code symbol

Puncturing rate 4/6 4/6 4/6 4/6 Modulation symbols per repeated symbol

Effective code rate

3/4 3/4 3/4 3/4

Modulation symbol rate

19,200 19,200 19,200 19,200 Sps


64 64 64 64 PN chips per modulation symbol

PN chips per bit 85.33 170.67 341.33 682.67 PN chips per bit


Issue II Rev 4

Forward Link

_________________________________________________________ Forward Traffic Channel

The forward traffic channels are used to transmit user data and signalling information. The forward traffic code channels are separated by their unique Walsh code assignments. Once a Walsh code in a cell or sector is assigned to any mobile, the same code cannot be assigned to any other mobile in that cell or sector during entire duration of the call. A forward traffic channel can be comprised of a fundamental code channel and supplemental code channels

Forward Code Channel

The fundamental forward code channel is used to transmit user data, signalling and the power control sub-channel

Supplemental Code Channel

Supplemental code channels may be used to provide the subscriber with a high speed data capability. The bit rate of a single fundamental code channel is limited by the rate set frame formats. A forward traffic channel may include several supplemental channels to provide the required bit rate. Each supplemental code channel requires an additional unique Walsh code assignment. The supplemental code channels always transmit at the maximum rate for the rate set in use and do not carry any signalling or power control sub-channel information. Supplemental code channels are a TIA/EIA – 95 capability and are not defined in IS-95A.


Issue II Rev 4

Forward Traffic Code Channels

• Fundamental Code Channel • Supplemental Code Channel

Fundamental Code Channel Walsh Code j is used for fundamental code channel:

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Issue II Rev 4

Reverse Link

_________________________________________________________ Reverse Link

The reverse link is separated from the forward link by 45 MHz at cellular frequencies and 80 MHz at PCS frequencies. The reverse link uses the same 32,768 chip code as that used on the forward link. The reverse link channels are either access channels or reverse traffic channels. The revere traffic channel is further divided into a single fundamental code channel and 0 to 7 supplemental code channels. There are 62 traffic channels and up to 32 access channels.

Access Channel

The access channel is used by mobile station to communicate with nontraffic information, such as originating calls and responding to paging. The access rate is fixed at 4800 bps. All mobile stations accessing a radio system share the same frequency assignment. Each access channel is identified by a distinct access-channel long-code sequence having an access number, a paging channel number associated with the access channel and other system data. Each mobile station uses a different PN code; therefore the radio system can correctly decode the information from an individual mobile station. The data transmitted on reverse channel is grouped into 20 ms frames. All data on the reverse channel is convolutionally encoded, block interleaved and modulated by modulation symbols transmitted for each 6 code symbols. The modulation symbol is one of 64 mutually orthogonal waveforms that are generated using Walsh functions.

Traffic Channel

The reverse traffic channel may use one of 9600,4800,2400 or 1200 bps data rates for transmission. The actual burst transmission rate is fixed at 28,800 code symbols per second. Since 6 code symbols are modulated as one of 64 modulation symbols for transmission, the modulation symbol transmission rate is fixed at 4800 symbols per second. This results in fixed Walsh chip rate of 307.2 kilo-chips per second. The rate of spreading PN sequence is fixed at 1.2288 Mcps so that each Walsh chip is spread by 4 PN chips.


Issue II Rev 4

Access Channels • Shared by all users • Aloha type contention process • Speed 4800 BPS • Equivalent to RACH in GSM • Used for call initiation, paging response and registration with the

system (like location updates ) • Ack for access is via paging channel. • Congestion Back off facility available.

Traffic Channels • Unique Sub addressing through Long Codes • 242 addresses possible. • Speed upto 9600 BPS • 20 msec frames • Use in band signalling with messages interleaved with speech.

Reverse Link Channelziation

Reverse CDMA Channels

AccessChl 1

AccessChl n

TrafficChl 1

TrafficChl 2

TrafficChl n

Access Channels:• Speed 4800 BPS• Like RACH in GSM• Originate calls / respond to pages• Used for registration with the system• Use Aloha like contention• Provide congestion back offs• Ack for access through paging channel

Reverse Traffic Channel:•Unique LOng code for sub addressing•242 addresses possible•20 msec frames•carry speech and data•speeds upto 9600 BPS•Use in band signalling with messages interleaved with speech signals.


Issue II Rev 4

Section 5

THE REVERSE CHANNEL


Issue II Rev 4

Section 5 The Reverse Channel 94 Objectives 96 Reverse Channel 97 Reverse channel structure 99 Convolutional coding 101 Block Interleaving 103 Orthogonal Modulation 109 Walsh code look up table 111 Data burst Randomizer 113 The Reverse channel-Spreading Methods 115 Frame structure 117 Reverse Channel-Traffic frames 119 Demodulation of Reverse channel 121


Issue II Rev 4

Objectives

_________________________________________________________ Objectives


Specify different classes of mobiles/hand sets. Explain the idea of controlled output power and gated output power. Explain the Reverse channel structure. With reference to the block schematic of the reverse channel, explain

the functions of each block. Explain the read-write operations in the block interleaver Explain how orthogonal codes are generated. Outline the concepts of Power control groups, data burst

randomization and long codes. Detail the frame structures of the reverse channel.


Issue II Rev 4

The Reverse Channel

_________________________________________________________ Mobile / Handset Power Limits

The maximum output power is specified for 3 different classes of handsets. Mobile Station Class ERP shall Exceed ERP shall NOT

Exceed. I 1 dBW ( 1.25 watts ) 8 dBW ( 6.3 watts ) II -3 dBW ( 0.5 watt ) 4 dBW ( 2.5 watts ) III -7 dBW ( 0.2 watt ) 0 dBW ( 1.0 watt )

All power levels are with reference to the antenna connector point, unless otherwise specified.

The power output of the handset is controlled either in the “ open loop Power Control ” method - here the mobile estimates the control required and adjusts its own power output- or the “ closed loop Power Control” method where both the mobile and the base station are involved in the power control mechanism. The Power control mechanism is described in detail in a separate section later.

Minimum Controlled Output Power

With both the open loop and closed loop power control methods, the mean output of the handset should be less than - 50 dBm/1.23 MHz i.e., -111 dBm/Hz. Implementing the power control methods in CDMA is very useful in reducing the near-far interferences. If all the mobiles within the coverage of a cell have their power controlled, then the total signal power received at the cell from all such mobiles would equal the nominal receive power times the number of mobiles.

Gated Output Power

The hand set shall transmit a nominal controlled power during gated periods. A typical output in a gated period is shown in the diagram opposite. The transmitter noise floor should be better than -60 dBm. During the OFF portions of the gated transmission, the handset should reduce the power either by 20 dB min. or to the noise floor level, whichever is greater. For example, if the gated on period power is say .5 watt. i.e., 27 dBm. Then the gated off period power will be 7 dBm, being greater than the noise floor level.


Issue II Rev 4

The Reverse Channel Mobile/ handset Output Power Limits

• All Power outputs are with reference to the antenna connector points. • Mobile Power is controlled either by Open Loop ( Mobile estimated ) or by

Closed Loop ( involves both the mobile and the base station ). • The power control helps eliminate the near-far interferences. • Typical output of the handset is defined by a mask shown below:

20 dB or to theNoise Floor

6 microseconds

3 dB

1.25 mSec

Mean output powerof the ensembleaverage.( reference line

Transmission Envelope Mask - Average Gated-on Power Control Group


Issue II Rev 4

The Reverse Channel Structure

_________________________________________________________ The Reverse Channel Structure

The Reverse Channel structure is shown in the diagram opposite.

The data is transmitted • In 20 msec frames. • The data is convolutionally coded. • Block interleaved • Subject to 64-ary orthogonal Modulation • Direct Sequence spread prior to actual transmission.

The reverse channel data comes in sizes of 172/80/40/16 bits per frame. To this we add Frame Quality Indicators ( for 4800 and 9600 bit rates ) and 8 Encoder Tail Bits. This will give transmit data rates of 9600, 4800,2400 and 1200 BPS. The traffic channels may use any of these rates while the Access channel uses only 4800 BPS speed.

The duty cycle of the transmitted data varies with the data rate. For 9600 it is 100% and for 1200 it is 12.5%. It varies by 50% for each speed.

• The burst transmission rate is fixed at 28,800 code symbols per second.

• 6 code symbols are modulated as ONE of 64 modulation symbols (Walsh Code ).

• The modulation symbol rate, therefore is 28,800÷6 = 4800 mod. symbols per second.

• This results in a Walsh Chip Rate of 4800x64 = 307.2 kcps. • Each Walsh chip is spread by 4 PN chips. • Hence the net rate of the spreading PN sequence is 307.2x4 =

1.2288 Mcps.

The figures are identical for the access channel except that the bit rate is fixed at 4800 BPS after adding the tail bits. Each code symbol is repeated once, to get 9600 bit rate and the duty cycle is 100%.


Issue II Rev 4

CDMA Reverse Channel Structure

Traffic ChannelInfo bits172/80/40/16bits per frame

8.6 kbps4.0 kbps2.0 kbps0.8 kbps 9.2 kbps

4.4 kbps2.0 kbps0.8 kbps

9.6 kbps4.8 kbps2.4 kbps1.2 kbps

28.8 kbps14.4 kbps 7.2 kbps 3.6 kbps

Add FrameQualityIndicators for 9600 & 4800BPS rates

Add 8 bitEncoderTail

Convolutional Encoder r=1/3; k=9

SymbolRepetition

Block Interleaver

64-aryOrthogonalModulator

Data BurstRandomiser

Long CodeGenerator

Base bandFilter

Base bandFilter

28.8 kbps

Modulation symbolWalsh Chip

4.8 ksps307.2 kcps

28.8 kbps

Frame Data rate

+I - Channel Sequence1. 2288 Mcps

Q - Channel Sequence1. 2288 Mcps

Long code Mask

PN Chip1. 2288Mcps

D

I

Q

+

+

+

+

+

cos ( wct )

sin( wct )

o/p

Code Symbol Code Symbol

Code Symbol

Delay= Tc/ 2406.9 nSec

i/p


Issue II Rev 4

Convolutional Coding

_________________________________________________________ Convolutional Coding

Covolutional coding is an FEC method to achieve required signal to noise ratio necessary to achieve acceptable error rate. Convolutional Coding involves modulo-2 addition (Exclusive-OR) of select tappings from a serially delayed data sequence as shown in the diagram. The data sequence delay is equal to K-1, where K is the constraint length of the encoder. The handset convolutionally encodes the reverse traffic and access channels prior to interleaving. The convolutional encoder of rate 1/3 and has a constraint length of 9 is used for Rate Set 1 Vocoder. When Rate Set 2 is in use, a rate 1/2 code is used. For 1/3 rate convolutional coder, for every input data bit, the encoder gives 3 output bits. The coder has 3 modulo-2 adders defined by what are known as generating polynomials g0,g1 and g2. The output is available at C0, C1 and C2.

Convolutional coding enables the system to work at a much lower values of Eb/N0 for the same level of performance. For example, if we need an Eb/N0 of 10 dB for a BER of 10-6, then we can get the same level of performance at an Eb/N0 of say, 7-8 dB, if convolutional coding is used. That is why almost all radio mobile systems use Convolutional (channel) coding.

Code Symbol Repetition

If the data rate is less than 9600 bps, then the output of the convolutional coder is passed through a code symbol repeater. 4800 bps is repeated once ( each symbol occurs 2 times ), 2400 is repeated 3 times ( each symbol occurs 4 times ) and so on. The repeated symbols are input to the interleaver and all BUT ONE of the code symbol repetitions are DELETED PRIOR to transmission.

However, for the Access channel which has a fixed bit rate of 4800 bps, the symbols are repeated once and BOTH the repeated code symbols are transmitted.


Issue II Rev 4

Reverse Channel Traffic ChannelInfo bits172/80/40/16bits per frame








SymbolRepetition

Block Interleaver



Long CodeGenerator

Base bandFilter

Base bandFilter

28.8 kbps


4.8 ksps307.2 kcps

28.8 kbps

Frame Data rate

+

I - Channel Sequence1. 2288 Mcps


Long code Mask

PN Chip1. 2288Mcps

D

I

Q

+

+

+

+

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cos ( wct )

sin( wct )

o/p


Code Symbol


i/p


+

+

+

g2

g1

g0

C2

C1

C0

Info bitsinput

Code Sumbols.Output

Block Schematic of a 1/3 rate Convolutional Encoder.

Issue II Rev 4

Block Interleaving ______________________________________________________ Block Interleaving

Just as in GSM, the data is interleaved, to protect it against noise bursts. However, in CDMA, the interleaving algorithm is different for different data rates. The interleaver is basically an array of 32 ROWs and 18 COLUMNs. The data (code symbols, including the repeated symbols) is WRITTEN into the array by COLUMNs and read out by ROWs. Block interleaving is performed over the span of one traffic channel frame.

Interleaver Write Operation

The interleaver array format for 9600 bps is given in the Table opposite. The write sequences for 4800 bps (which includes the Access channel also), 2400 and 1200 bps are shown in Tables on the next 2 pages. For these speeds, the columns are repeated as many times as the data was repeated. For example, at 4800 bps, the data was repeated once; the first 2 rows of column 1 are numbered 1, the next 2 rows of column 1 are numbered 2 and so on. For this speed, you will find that the 2 rows are identical, leaving 16 such sets. For 2400 bps, 4 rows would be identical and for 1200 bps, 8 rows would be identical.

Interleaver Read Operation

As said earlier, the data is read out of the interleaver by the rows. The read sequence varies with data rate. For 9600 bps, the read sequence is:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

For 4800, the sequence is:

1 3 2 4 5 7 6 8 9 11 10 12 13 15 14 16 17 19 18 20 21 23 22 24 25 27 26 28 29 31 30 32

For 2400 bps, the sequence is:

1 5 2 6 3 7 4 8 5 9 13 10 14 11 15 12 16 17 21 18 22 19 23 20 24 25 29 26 30 27 31 28 32

At 1200 bps, the sequence is:

1 9 2 10 3 11 4 12 5 13 6 14 7 15 8 16 17 25 18 26 19 27 20 28 21 29 22 30 23 31 24 32

For the Access channel, the sequence is different, though at 4800 bps.

1 17 9 25 5 21 13 29 3 19 11 27 7 23 15 31 2 18 10 26 6 22 14 30 4 29 12 28 8 24 16 32


Issue II Rev 4

Block Interleaving Traffic ChannelInfo bits172/80/40/16bits per frame








SymbolRepetition

Block Interleaver



Long CodeGenerator

Base bandFilter

Base bandFilter

28.8 kbps


4.8 ksps307.2 kcps

28.8 kbps

Frame Data rate

+



Long code Mask

PN Chip1. 2288Mcps

D

I

Q

+

+

+

+

+

cos ( wct )

sin( wct )

o/p


Code Symbol


i/p

Block Interleaving Algorithm for 9600 bps rate

• Data is written into the array by columns. • Data is read out of the array by rows. • The rows are repeated while writing by the number of times the data

was repeated by the symbol repeater. • The read sequence is different for different data rates and for the

Access Channel. Columns 1 to 18 Row No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 1 33 65 97 129 161 193 225 257 289 321 353 385 417 449 481 513 5452 2 34 66 98 130 162 194 226 258 290 322 354 386 418 450 482 514 5463 ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... 4 ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... ..... ..... ..... ..... 32 32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 512 544 576 At 9600, the data is read out row by row continuously.


Issue II Rev 4

Block Interleaver

_________________________________________________________ Block Interleaver writing Algorithm For 4800 bps rate

Refer to table 1for 4800 bps rate block interleaver algorithm Block Interleaver writing Algorithm for 2400 bps

Refer to table 2for 2400 bps rate block interleaver algorithm


Issue II Rev 4

Table 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 1 17 33 49 65 81 97 113 ..... ..... ..... ..... ..... ..... .... ..... 257 273 2 1 17 33 49 65 81 97 113 ..... ..... ..... ..... ..... ..... ..... ..... 257 273 3 2 18 34 50 66 82 98 114 ..... ..... ..... ..... ..... ..... ..... ..... 258 274 4 2 18 34 50 66 82 98 114 ..... ..... ..... ..... ..... ..... ..... ..... 258 274 .... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .... .... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... 31 16 32 48 64 80 96 112 128 ..... ..... ..... ..... ..... ..... ..... ..... 272 288 32 16 32 48 64 80 96 112 128 ..... ..... ..... ..... ..... ..... ..... ..... 272 288

Table 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 1 9 17 25 33 ... ... ... ... ... ... ... ... ... ... ... 129 137 2 1 9 17 25 33 ... ... ... ... ... ... ... ... ... ... ... 129 137 3 1 9 17 25 33 ... ... ... ... ... ... ... ... ... ... ... 129 137 4 1 9 17 25 33 ... ... ... ... ... ... ... ... ... ... ... 129 137 5 2 10 18 26 34 ... ... ... ... ... ... ... ... ... ... ... 130 138 6 2 10 18 26 34 ... ... ... ... ... ... ... ... ... ... ... 130 138 7 2 10 18 26 34 ... ... ... ... ... ... ... ... ... ... ... 130 138 8 2 10 18 26 34 ... ... ... ... ... ... ... ... ... ... ... 130 138 ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 29 8 16 24 32 40 ... ... ... ... ... ... ... ... ... ... ... 136 144 30 8 16 24 32 40 ... ... ... ... ... ... ... ... ... ... ... 136 144 31 8 16 24 32 40 ... ... ... ... ... ... ... ... ... ... ... 136 144 32 8 16 24 32 40 ... ... ... ... ... ... ... ... ... ... ... 136 144


Issue II Rev 4

Reverse Channel

________________________________________________________ Block Interleaving for 1200 bps

Refer to page opposite for 1200 bps block interleaver algorithm


Issue II Rev 4


Table 3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 2 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 3 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 4 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 5 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 6 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 7 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 8 1 5 9 ... ... ... ... ... ... ... ... ... ... ... ... ... 65 69 9 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 10 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 11 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 12 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 13 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 14 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 15 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 16 2 6 10 ... ... ... ... ... ... ... ... ... ... ... ... ... 66 70 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 25 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 26 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 27 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 28 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 29 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 30 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 31 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72 32 4 8 12 ... ... ... ... ... ... ... ... ... ... ... ... ... ... 72

Issue II Rev 4

Orthogonal Modulation _________________________________________________________ Orthogonal Modulation

The base station must demodulate the mobile transmission non-coherently. To improve non-coherent demodulation, Orthogonal Modulation scheme is employed. In this technique, instead of transmitting antipodal signal +1 and –1, a set of orthogonal signals will be used. The signal duration should be as long as possible but not longer than the coherence time of the channel (the time frame during which the channel is relatively stable). Walsh codes are used for this purpose. On the forward link, the Walsh codes isolated one scriber from another. In reverse link, the Walsh codes will provide isolation between symbols. The orthogonal signalling set contains 64 possible signals. The information to be modulated is segregated into groups of 6 symbols. These 6 symbols then correspond to a value from 0 to 63. This value is used to select a Walsh code for transmission.

Orthogonal Modulator

The output of the block interleaver is passed through the 64-ary Orthogonal Modulator. The orthogonal codes are generated according to a recursive matrix form defined below:

H1 = 0; H2 = 0 0 0 1 H4 = 00 00 01 01 00 11 01 10

Or, in general, H2n = Hn Hn Hn ⎯Hn where n is a power of 2.

The modulation symbol has a rate of 4800 symbols per second and the duration of each modulation symbol is 1/4800; i.e., 208.333...µ sec. The time associated with 1/64 th of the modulation symbol is called the Walsh Chip and is equal to 1/307200 sec; i.e., 3.255 µSec. The code symbols are taken in 6 bit blocks and converted into corresponding decimal number. From the Walsh code look up table, a 64 bit Walsh code corresponding to this decimal number is output.

The Walsh Code Look up Table is given in the next pages.


Issue II Rev 4

Orthogonal Modulation Traffic ChannelInfo bits72/80/40/16

s per frame








SymbolRepetition

Block Interleaver



Long CodeGenerator

Base bandFilter

Base bandFilter

28.8 kbps


4.8 ksps307.2 kcps

28.8 kbps

1bit

Frame Data rate

+



Long code Mask

PN Chip1. 2288Mcps

D

I

Q

+

+

+

+

+

cos ( wct )

sin( wct )

o/p


Code Symbol


i/p


Issue II Rev 4

Walsh Code Lookup Table

_________________________________________________________ Walsh code Lookup table

For example for the input code of 100010, Walsh Code no 34 is sent for an input of 101101, Walsh code number 57 is sent and so on.


Issue II Rev 4

Walsh Code Lookup Table

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 630 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 01 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 12 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 13 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 04 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 15 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 06 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 07 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 018 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 19 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0

10 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 11 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 112 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 013 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 114 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 115 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 016 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 117 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 018 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 19 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 120 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 021 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 122 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 123 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 024 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 025 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 126 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 127 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 028 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 129 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 030 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 031 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0132 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 133 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 034 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 35 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 136 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 037 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 138 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 139 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 040 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 041 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 142 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 143 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 044 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 145 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 046 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 047 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0148 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 049 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 150 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 151 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 052 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 153 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 054 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 055 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 0 1 1 0 1 0 0156 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 157 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 058 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 59 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 160 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 061 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 162 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 163 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0 0 1 1 0 1 0 01 0 1 1 0 1 0 01 1 0 0 1 0 1 1 0


Issue II Rev 4

Data Burst Randomizer _________________________________________________________ Power Control Groups

Each 20 msec reverse traffic channel frame is divided into 16 slots of 1.25 ms each. These slots are numbered 0 to 15 and are called power control groups. A power control group contains 12 bits or 36 code symbols (because of 1/3 convolutional coding) or 6 modulation symbols (because of Walsh Coding)

Data Burst Randomizer

When there are periods of reduced speech activity, the vocoder will reduce its data rate allowing the transmission of the signal at a lower average level of power. On the forward traffic channel, this is done by repeating symbols and then transmitting each symbol at reduced power. The disadvantage of this method is that it spreads bit energy out over time. It takes longer to collect the energy at the receiver. The requirement for rapid power control of the reverse traffic channel necessitated the use of alternative of reducing average power. On the reverse traffic channel, the mobile uses full rate power when it transmits. When redundant information is produced by the symbol repetition scheme, the data burst randomizer will turn off the transmitter, reducing the average transmission power. The “Gating Off” of the transmitter is done pseudorandomly. For example, at 9600 bps, the gate allows all the symbols from the interleaver output to be transmitted; for 4800, on half the output is sent and so on. This is done on specific power control groups. The groups are “gated off” to stop transmission. The gated-on groups are pseudo-randomized in their position within the frame. This data burst randomization ensures that every code symbol input to the repetition process is transmitted exactly once. The access channels are not randomized.

Long Code Generator

Long codes are used for uniquely identifying each traffic channel on the reverse link. They are also used for randomizing the data bursts as will be explained later. The long code has a duration of 242-1 chips. If the offsets are 64 chips apart, i.e., 26, then we get a total of 236 possible long code offsets for the reverse link traffic channels and access channels. This means approximately 70 billion possible offsets. Of these, a subset is reserved for access channels and the rest are used for traffic channels.


Issue II Rev 4

Data burst Randomizer Traffic Channel Info bits 172/80/40/16 bits per frame

8.6 kbps 4.0 kbps 2.0 kbps 0.8 kbps 9.2 kbps

4.4 kbps 2.0 kbps 0.8 kbps



Add Frame QualityIndicators for 9600 & 4800 BPS rates



Symbol Repetition

Block Interleaver

64-ary Orthogonal Modulator


Long CodeGenerator

Base band Filter

Base band Filter

28.8 kbps

Modulation symbol Walsh Chip

4.8 ksps 307.2 kcps

28.8 kbps

Frame Data rate

+



Long code Mask

PN Chip1. 2288Mcps

D

I

Q

+

+

+

+

+

cos ( wct )

sin( wct )

o/p


Code Symbol

Delay= T c / 2 406.9 nSec

i/p

Power Control Groups • The traffic channel frame (20 ms) is divided into 16 slots of 1.25 ms each. • The slots are numbered 0 to 15 and are called Power Control Groups. • Each group has 12 bits or 36 code symbols or 6 mod symbols.

Data Burst Randomization • Done by gating-on or off a power control group. • Gated-on groups are pseudo randomized within the frame. • The gating ensures that the code symbol input to the repetition process is

transmitted only once. • At 9600, all symbols are sent; at 4800, one half the symbols are sent and

at 2400, one fourth symbols are sent and so on. • Data randomizer generates a masking pattern decided by the data rate

and a block of 14 bits from the long code used for spreading. • The Access Channels are not randomized.

Long Codes • Used for randomizing data bursts. • Also provide a unique offset for the channels on the reverse link. • The codes have a cycle time of 242-1 chips. • If the offsets are 64 chips apart, then 236 different offsets are possible.

This means about 70 billion offsets!! © MOTOROLA LTD.2003 CDMA02: Principles of CDMA Page 114 / 425 FOR TRAINING PURPOSES ONLY South Asia Network Solutions Division Bangalore, India

Issue II Rev 4

The Reverse Channel – Spreading Methods _________________________________________________________ Long Code Mask

The PN generator is masked with same mask that was used to scramble the forward traffic channel. The data burst randomizer generates a “ masking pattern ” of ‘0’s and ‘1’s that randomly mask out the redundant data generated by the code repetition process. The masking pattern is determined by the data rate and by a block of 14 bits taken from the long code. These 14 bits are the last bits of the long code used for spreading in the last but one power control group of the previous frame. The data burst randomization algorithm is explained in Appendix

Direct Sequence Spreading The signal out of randomizer is then spread using long PN code. At this point the signal already occupies a bandwidth of 307.2 Khz due to orthogonal modulation. PN spreading increases bandwidth by 4 times to total of 1.23 MHz. The spreading operation involves modulo-2 addition of randomizer output and the long code. The mask varies depending on the channel type on which the mobile is transmitting. The mask for access channel is as shown in the diagram. For the traffic channel, the system uses either a “public long code mask ” or a “ private long code mask”. The masks for access and traffic channels are shown in the diagram.

Quadraure Spreading

After the direct sequence spreading, the signals are quadrature modulated by spreading them into I and Q channels; for this we use 2 PN sequences called the I and Q pilot PN sequences. Short PN codes are used for this purpose, but no offset is applied. All mobiles use zero offset.

These sequences are periodic sequences of period 215 chips. The sequences are generated according to the characteristic polynomials defined by:

PI (x) = x15 + x13 + x9 + x8 + x7 + x5 +1 and PQ(x) = x15 + x12 + x11 + x10 + x6 + x5 + x4 + x3 +1

The above polynomials have a period of 215-1 and are generated using recursive shift register configurations with tappings at specific stages.The pilot PN sequences repeat every 26.666... msec (= 215 / 1228800 secs) and there are exactly 75 such repetitions every 2 seconds. The data spread by the Q channel is delayed by 406.901 nsec (i.e., by half a chip duration ) with reference to the I channel data. The reverse channel I and Q mapping and the resultant constellations are shown in the diagram opposite.

Base band Filtering The output of the quadrature spreading circuit is then passed through a base band filter.


Issue II Rev 4

Direct Sequence Spreading • The spreading is done by modulo-2 addition of the randomizer output and the

long code. • For traffic channels, the system uses either a “Public” long code mask or a

“Private” Long code mask. The masks used for access and traffic channels are shown below:

•

A ccess Channel Long Code M ask

41 33 32 28 27 25 24

110001111 ACN PCN Base

9 8 0

_ID Pilot_PN

AC N - Access C hannel Num ber.PC N - Paging C hannel Num ber.

Base_ID - Base station IdentificationP ilot_PN - PN offset for the forw ard CD M A channel.

41 32 31 0

1100011000 Perm uted Electronic Serial Num ber ( ESN )

Public Long Code M ask

I-Q Mapping and Constellation:


I - c h a n n e l

Q - c h a n n e l

0 0

0 1

1 0

1 1

I Q P h a s e

0 0 4 5 0

1 0

1 1

0 1 - 4 5 0

1 3 5 0

- 1 3 5 0

I - Q C h a n n e l M a p p i n g

R e v e r s e C D M A c h a n n e l c o n s t e l l a t i o n a n d p h a s e t r a n s i t i o n

Issue II Rev 4

Frame Structure __________________________________________________________ Frame Structure of Access Channels

The access channel is generated in the same manner as the reverse traffic channel with once exception already mentioned above: the data burst randomizer is not used. The data random burst randomizer is used to reduce average power when speaker activity subsides. There is no speech activity on the access channel. Modulation rate is fixed at 4800 bps. The reverse channel may have up to 32 Access channels (numbered 0 to 31), per Paging channel. Each access channel is associated with a single paging channel on the corresponding forward CDMA channel. (The forward CDMA channel is described in the next section).

Time Alignment

An access channel frame shall begin only when the system time is an integral multiple of 20 ms. The synchronization, timing and structure of the access channel will be described later.

The Access channel consists of 96 bits (4800 bps, 20 ms frames). Each frame has 88 information bits and 8 encoder Tail bits. The Access channel has a pre amble of frames of 96 zeros to help the base station to acquire the access channel transmission.

Frame Structure of Reverse Traffic Channel

The characteristics of reverse traffic channels are given below: o Variable data rates 9600 to 1200 bps o Frame duration is 20 ms. o For 9600 bps, each frame has 192 bits with 172 info bits, 12 bits

of Frame Quality Indicator (CRC) and 8 tail bits. o The generator polynomial is x12+x11+x10+x9+x8+x4+x+1

o At 4800 bps, we have 96 bits per frame with 80 info bits and 8 bits for Frame Quality Indicator and Tail bits.

o The generator polynomial is x8+x7+x4+x3+x+1 o At 2400 and 1200 bps speeds we have 8 Tail bits with 40 and 16

info bits respectively. o The Tail bits are all ‘0’s. o A handset may support staggered Traffic channel frames. The

time offset is specified by the “ FRAME_OFFSET” parameter in the data base. A zero offset traffic channel can begin only when the system time is an integral multiple of 20 ms. A staggered frame begins 1.25 x FRAME_OFFSET ms later than the zero offset traffic channel frame. The reverse channel interleaver will be aligned with the traffic channel frame.


Issue II Rev 4

Frame Structures

A c c e s s C h a n n e l F ra m e S tru c tu re9 6 b its (2 0 m s e c )

8

8

88

8

8

T

1 2

F T

T

T

T

F

1 9 2 b its (2 0 m s e c )

9 6 b its (2 0 m s e c )

4 8 b its (2 0 m s e c )

2 4 b its (2 0 m s e c )

8 8

9 6 0 0 b p s F ra m e S tru c tu re

1 7 2

8 0

4 0

1 6

4 8 0 0 b p s F r a m e S tru c tu re



• Access channel has Preamble frames of 96 bits. This helps the base station to

detect and lock onto an access channel.


Issue II Rev 4

Reverse channel – Traffic frames

_________________________________________________________ Reverse Channel

Though the general frame structure for the access and traffic channels has been discussed in the previous page, the traffic frame structure depends on whether it carries primary traffic or secondary traffic. These two terms are discussed below:

Primary Traffic

The main traffic between the mobile and the base station is called the Primary Traffic.

Secondary Traffic

Some times an additional traffic stream could also be transmitted along with the primary traffic data. This additional traffic is called the Secondary traffic data. The signalling associated with the primary and secondary traffic is called Primary and Secondary signalling traffic respectively.

Dim- and -Burst

A frame in which the secondary traffic is combined with the primary traffic is called a Dim and Burst frame. The frame structures given in the previous page are modified to show the primary and secondary traffic/signalling, as shown in the diagram opposite. Frame structures for 9600 bps speed only are shown. For other speeds, there are NO SEPARATE SIGNALLING TRAFFIC OR SECONDARY TRAFFIC DATA BITS; the frames for these lower speeds carry only primary/ regular traffic information.

Notations of Frame Structures

MM bit: Mixed Mode Bit: ‘0’-Primary Traffic only

‘1’-Primary trafficand / or signalling traffic or secondary traffic.

TT bit: Traffic Type bit: ‘0’- Signalling bit; ‘1’- Secondary traffic

TM bits: Traffic Mode bits: 00 -- 80 primary traffic data bits and either 88 signaling traffic bits or 88 secondary traffic data.

01 -- 40 bits of primary data and either 128 bits of secondary traffic or signalling data.

10-- 16 bits of primary data and 152 bits of signalling or secondary traffic data. 11 --168 bits of either signalling or secondary traffic.


Issue II Rev 4

Reverse Channel

o The type of reverse channel frame sent depends on type of traffic/ signalling information it carries.

Primary and signalling Traffic Frames

172 bits

1 171 bits primary traffic

1 1 2

1 1 2

1 1 2

1 1 2

MM= 0

MM TT TM= 1 =0 =00

MM TT TM= 1 =0 =01

MM TT TM= 1 =0 =10

MM TT TM= 1 =0 =11

80 bits primary tfc 88 bits signalling tfc

40 bits pri. tfc 128 bits signalling tfc

16 pri 153 bits signalling tfc

168 bits signalling tfc

9600 bps primary traffic only

Dim and Burst with Ratte 1/2 Primaryand Signalling Traffic



Blank and Burst with signallingTraffic Only

• Alternatively, if the secondary traffic option is used then we will have secondary traffic data bits in place of signalling bits shown above.

• For other lower speeds, there is no separate signalling/secondary traffic. • Frames for these rates carry only the regular/ primary traffic information.


Issue II Rev 4

Demodulation of Reverse channel

_________________________________________________________

Demodulation of Reverse CDMA channel IS-95A standard does not specify details on modulation. So, only brief overives of the structure and processes performed in the demodulators are presented here.

The signal is down converted from 800 MHz or 1.9 GHz bands down to baseband. The down conversion normally takes several steps

Analog to Digital conversion is performed on down converted data

Base station also implements Rake Receiver. The correlators perform a product integration in order to

despread the short PN codes. Walsh code modulation symbols are detected

Combiner combines outputs of fingers non-coherently Signal is then de-interleaved Viterbi decoder does not know the rate of the vocoded frame

and must decode at all four rates and then use metrics to decide which rate was most likely rate transmitted


Issue II Rev 4

Demodulation of Reverse CDMA Channel

Finger 1

Finger 2

Finger 3

Finger 4

Finger 1

C O M B I N E R

© MOTOROLA LTD.2003 CDMA02: Principl FOR TRAINING PUR South Asia Network So Bangalore,

De-Interleaver

U/D

Power Control Decision
Command
es of CDMA Page 122 / 425 POSES ONLY lutions Division India

Issue II Rev 4

Section 6

THE FORWARD CHANNEL


Issue II Rev 4

Section 6 The Forward Channel 123 Objectives 125 Forward Channel 126 Forward Channel frame structure 128 Walsh Codes 130 Pilot Channel 132 The Sync Channel 134 Block Interleaving 136 The structure of Sync channel 138 Paging Channel 140 Paging Channel Structure 142 Paging channel messages 144 Forward traffic channel 148 Forward – Power control sub channel 150 Power control 152 Open loop power control 154 Near-Far problem in the reverse link 156 Near-far problem – Forward link 158 Closed loop power control 160 Forward channel-Power control sub channel 162 System timing aspects 166


Issue II Rev 4

Objectives

_________________________________________________________ Objectives

After completion of this section, the trainee is expected to be able to:

List and explain the functions and features of the various Logical Channels in the Forward and Reverse Channels. Explain the structure of different logical Channels. Explain the application of Walsh Codes in Forward and Reverse

channels. Explain the frame structure for the various logical channels. Explain the Power Control Mechanism in CDMA:

♦ Define the need for Power Control ♦ Specify types of Power Control. ♦ Explain hoe open loop power control is carried out. ♦ Explain the Near-Far problem in the Reverse and Forward

Links. ♦ Explain the concept of Power Control Groups. ♦ Explain with the help of a simple schematic of the frame

structure, how power control is effected.


Issue II Rev 4

The Forward Channel

_________________________________________________________ The Forward Channel

The forward channel is from the base station to the mobile or subscriber hand set and comprises the following:

• The Pilot Channel • The sync Channel • The Paging Channel • The Forward Traffic Channel

o Fundamental Code Channel o Supplemental Code Channel (max 7)

The transmit frequency is 45 MHz away from the reverse link frequency and has 1.23 MHz bandwidth. The channels all use Walsh Codes and 64-ary orthogonal codes for modulation. The general structure is shown in the opposite page. The pilot channel is the first Walsh code number W0. There are up to 7 Walsh codes for the Paging Channel and the Sync channel takes the Walsh Code number W32.

The Forward Traffic channels carry information pertaining to the Mobile Power Control also.


Issue II Rev 4

General Structure of the forward channel

Forward CDMA Channel

W0 W1 W2 W7 W32 W8 W30 W31 W33 W63

Pilotupto 7 pagingchannels. Unused paging channelscarry traffic.

Traffic ChannelsSyncchannel

Traffic dataMob.Pwrcontrolsub.chl


Issue II Rev 4

The Forward Channel Frame Structure

Forward Traffic Channel Frame Structure

_________________________________________________________

The forward traffic channels are grouped into rate sets. Rate Set 1 has four elements: 9600, 4800, 2400 and 1200 bps. Rate Set 2 uses four elements: 14,400, 7200, 3600 and 1800 bps. The quality of Rate Set 2 vocoder is superior to that of Rate Set1. The vocoder produces a frame every 20 ms using CELP (Code Excited Linear Prediction) technique.

Forward Traffic Channel Frame Structure for RS1

When the data rate on the forward traffic channel is 9600 bps, each frame of 192 bits carries 172 information bits, 12 frame quality bits and 8 encoder tail bits (set of all 0s). 172 information bits consist of 1 or 4 format bits. A variety of multiplexing options are supported. The entire 171 information bits can be used for primary traffic or 168 bits can be used for 80 primary traffic bits and 88 signalling traffic bits or 88 secondary traffic bits. Other options use 40 and 128 or 16 and 152 bits primary and signalling/secondary traffic. Alternatively, the entire 168 bits can be used for signalling or secondary traffic. Signalling messages can be Authentication challenge message, handoff direction message, alert with information message, neighbor list update message etc. At 4800 bps, each frame of 96 bits carries 80 information bits, 8 frame quality bits, and 8 tail bits. At 2400 bps, each frame of 48 bits carries 40 information bits, 8 tail bits. Finally, at 1200 bps, each frame of 24 bits carries 16 information bits and 8 tail bits. The base station can select the data transmission rate on a frame-by-frame basis. A data rate of 9600 bps can support multiplexed traffic and signalling. Data rates of 1200, 2400 and 4800 bps can support only primary traffic information. The frame quality indicator is a CRC on the information bits in the frame.


When the data rate on the forward traffic channel is 14,400 bps, each frame of 288 bits carries 267 information bits, 12 frame quality bits and 8 encoder tail bits. For other data rates, please refer to the diagram given in the opposite page.


Issue II Rev 4


© MOTOROLA LTD.2003 CDMA02: Principles of CDMA Page 129 / 425 FOR TRAINING PURPOSES ONLY South Asia Network Solutions Division

9600 bps

172 12 8

192 Bits (20 ms)

F T 96 Bits (20 ms) 4800 bps

80 8 8

F T 2400 bps

48 Bits (20 ms)

40 8

T


1200 bps

24 Bits (20 ms)

16 8

T

14400 bps

1 267 12 8

288 Bits (20 ms)

R/F F

7200 bps

T

3600 bps 1800 bps

1 125 10 8

R/F F T

144 Bits (20 ms)

1 55 8 8

R/F F T

72 Bits (20 ms) F= Frame quality indicator (CRC) T=Encoder bits R/F=Reserved/Flag bit

1 21 6 8

R/F F T

36 Bits (20 ms)

Bangalore, India

Issue II Rev 4

Walsh Codes

_________________________________________________________ Walsh Codes

All logical channels on the forward link are Direct Sequence Spread by using an appropriate Walsh Code. For instance, the pilot channel would be spread by using Walsh Code W0, pumped at the rate of 1.2288 Mcps. The paging channel would be spread by W1 and a traffic channel, say, 38 would be spread by Walsh Code W38 and so on.

The Walsh Codes are explained in the previous chapter.


Issue II Rev 4

Walsh Code Generation


Issue II Rev 4

Pilot Channel

_________________________________________________________

The pilot PN sequence offset is illustrated in the diagram opposite.

The Pilot Channel

The Pilot channel is transmitted always on the forward link, on each active Forward CDMA Channel. It is an unmodulated spread spectrum signal consisting of all ‘0’s. It helps the mobile/ hand set receiver to effectively perform coherent detection and provides the handset the required carrier phase and system timing references. The Pilot channel is directly modulated by the Walsh Code Number W0 at a PN chip rate of 1.2288 Mcps.

Pilot PN sequence Offset

Every base station uses a specific timing offset for the PN sequence to enable the receiver to identify a forward CDMA channel. The time offsets may be reused within a CDMA cellular network. There are 512 possible time offsets and are numbered 0-512. The offset index (0-512) specifies the offset value with reference to the zero offset Pilot PN sequence

The offset for a given PN sequence, in terms of chips, is equal to the offset number multiplied by 64. for example, if the offset index is 20, then the PN sequence is offset by 20x64=1280 PN chips. For the zero offset value, the PN sequence starts at the beginning of EVERY EVEN SECOND in time, with reference to the base station transmission time.

When the Pilot PN sequence is offset, say by 20, then the PN sequence will start 1.04166 ms AFTER the start of EVERY EVEN SECOND. (duration of a chip = 813.8 ns ; 813.8 x 10-9 x 1280 = 1.04166 ms)

The same offset is used on all CDMA frequency allocations for a given base station.


Issue II Rev 4

Pilot Channel Offset

• Each Base station uses a time offset of the Pilot PN sequence to identify a

forward CDMA channel. • 512 offset values ( 0 - 511 ) • The zero offset sequence starts at every even second. • The offset, in chips, is = Offset index * 64; for example, an offset index of 20

means that the PN sequence starts 1280 chips, i.e., 1280 x 813.8 nsec = 1.04166.. msec AFTER the beginning of EVERY even second.

• The same pilot PN sequence offset is used on all CDMA frequency assignments for a given base station.


Issue II Rev 4

The Sync Channel

_________________________________________________________ The Sync Channel

The Sync Channel operates at a fixed bit rate of 1200 bps. The block schematic for the sync channel is shown in the opposite page. It is used for the mobile to get the Timing and Long code references from the base station.

The sync data is passed through a convolutional coder of 1/2 rate and constraint length K=9. The output of the convolutional coder is 2400 bps and is passed through code repetition circuit to get 4800 bps.

The output of the repetition circuit is then block interleaved and subjected to direct sequence spreading using Walsh Code number 32 and then to a quadrature spreading circuit which is similar to the one used in the reverse channel.

The sync channel is NOT scrambled and does NOT carry the Power control sub channel.


Administrator

It is used for the mobile to get the Timing and Long code references from the base station.

Issue II Rev 4

The Sync channel

• It does NOT carry the power control bits.

• Operates at 1200 bps. • Used for the mobile to get Timing and Long code references. • It is NOT scrambled.

• Uses the same pilot PN offset as the Pilot chl.

The Sync Channel Block Schematic

ConvolutionCoderr=1/2;K=9

Symbolrepetition

Block Interleaver

WalshCode 32

PN chips1.2288 Mbps

A1200 bps

Code symbol

Modsymbol

2400bps

4800bps

Modsymbol4800bps

+

A

BPF

BPF

Cos Wct

Sin Wct

I chl

Q chl

I channel pilotPN sequence1.2288 mbps

Q channel pilotPN sequence1.2288 mbps

+

+

X

X

+s(t)

I (t)

Q (t)


Issue II Rev 4

Block Interleaving _________________________________________________________

The Sync Channel - Block Interleaving

The sync channel uses a block interleaver spanning 26.666.. msec., which is equal to 128 modulation symbols at a symbol rate of 4800 sps. The interleaving technique employed for the sync channel is called the bit reversal method.

As in the case of the reverse channel, here also the bits are written in to an array and read out in a particular order. The write and read sequences are given in Tables 1 and 2.

Let us illustrate the bit reversal method.

Assume a 4x4 matrix as shown below:

1 5 9 13


2 6 10 14 The data is written by columns. 3 7 11 15 4 8 12 16

The read sequence is by the Rows, as shown: 1 3 2 4

13 15 14 16

For bigger matrices, the choice of rows could be different, as shown in Table 2 given in the page opposite.

9 11 10 12 5 7 6 8

Bangalore, India

Issue II Rev 4

Table 1. Sync Channel Interleaver- writing sequence

1 17

The Sync Channel

9 25 33 41 49 57

1 9 17 25 33 41 49 57 2 10 18 26 34 42 50 58 2 10 18 26 34 42 58 50 3 11 19 27 35 43 51 59 3 11 19 27 35 43 51 59 4 12 20 28 36 44 52 60 4 12 20 28 36 44 52 60 5 13 21 29 37 45 53 61 5 13 21 53 29 37 45 61 6 14 22 46 54 30 38 62 6 14 22 30 38 46 54 62 7 15 23 31 39 47 55 63 7 15 23 31 39 47 55 63 8 16 24 32 40 48 56 64 8 16 24 48 64 32 40 56

4

Table 2. Sync Channel Interleaver array Read Sequence

1 3 2 4 1 3 2 33 35 34 36 33 35 34 36 17 19 18 20 17 19 18 20 49 51 50 52 49 51 52 50 9 11 10 12 9 11 10 12

41 43 42 44 41 43 42 44 25 27 26 28 25 27 26 28 57 59 58 60 57 59 58 60 5 7 6 8 5 7 6 8

37 39 38 40 37 39 38 40 21 23 22 24 22 24 21 23 53 55 54 56 53 55 54 56 13 15 14 16 13 15 14 16 45 47 46 48 45 47 46 48 29 31 30 32 29 31 30 32 61 63 62 64 61 63 62 64


Issue II Rev 4

The Structure of Sync Channel

_________________________________________________________ The Structure of the Sync Channel

We have seen earlier the characteristics and the block schematic of the sync channel; let us now have a closer look at its actual structure. See diagram in the opposite page. The sync channel is sent in 80 ms Super Frames. Each super frame contains three 26.666... ms sync frames. The first bit of each frame is the SOM (Start of Message) bit. A number of super frames are combined to get a SYNC CHANNEL MESSAGE CAPSULE. The message capsule consists of

• Sync channel message • Padding. • The sync Channel message consists of a length field (8

bits). The value of Message length is in octets and has a maximum value of 148 octets. This if the message length is 100, then it means 100 octets or 800 bits.

• Message body • CRC field.

The padding consists of zero or more bits. The padding bits are added to the end of the sync channel message so that total number of bits sent equal integer multiples of 93 bits. The padding bits are set to ‘0’.

The sync channel message body format is given in the Table below

Field No. of bits Remarks MSG_TYPE 8 Message Type. Set to “ 00000001 ” P_REV 8 Protocol Revision Level ( 00000010 ) MIN_P_REV 8 Min. P_REV. Only mobiles with P_REV numbers

greater than the minimum can access the system. SID 15 System Identity. NID 16 N/W Identity. The SID and NID are a pair to identify a

CDMA network. PILOT_PN 9 The base station sets this field to the offset number

given for this cell; it is in units of 64 PN chips. LC_STATE 42 Long code State. The long code state at the time given

by the SYS_TIME field in the message body. SYS_TIME 36 System time. ( Explained later in another section ) PRAT 2 Sets the paging channel data rate; 00 means 9600 bps;

01 means 4800 bps. Other combinations are reserved. Reserved 3 Set to 000.


Administrator

asshole remember this all of them SID NID Protocol revesion System Time Paging Rate Reserved

Administrator

Issue II Rev 4

The Sync Channel structure

• Sync Channel is sent in Super frames of 80 msec. • Each super frame has 3 frames of 26.666... msec each. • A number of super frames form a sync channel message capsule. • A capsule has a message length indicator, message body and

CRC.Message length is in octects. • It also has padding bits set to ‘0’; the number of padding bits is to make

the total number of bits equal to an integer multiple of 93 bits. • The beginning of a super frame has an SOM bit set to ‘1’ for the first

frame and set to ‘0’ for other frames.

Sync Channel Structure

80 msec; 96 bits

Sync Channel superframe Sync Channel superframe

Sync.chlFrame

Sync.chlFrame

Sync.chlFrame

Sync.chlFrame

Sync.chlFrame

Sync.chlFrame

SOM

SOM

SOM

SOM

SOM

SOM

1 0 0 0 0 0

Sync channel Message Capsule; = 93 x Ns ; Ns is number of superframes needed.

Sync Channel Message Padding ; as needed ; ‘0’s.

MSG_LENGTH Message Body CRC

8 bits 2 - 1146 bits 30 bits


Issue II Rev 4

Paging Channel

_________________________________________________________ The Paging Channel

The paging channel is a 9600 or 4800 bps, encoded, block interleaved signal used by the base station to transmit system overhead information and mobile specific messages. The paging channel is transmitted in 20 ms frames. The Paging channels use the same pilot PN sequence offsets as the pilot channel.

The interleaver output and the paging channel frame align with the beginning of the zero offset pilot PN sequence at every even second. i.e. at 0,2,4 ... seconds in time.

The block schematic of the paging channel arrangement is shown in the diagram opposite.

The long code mask used for the paging channel has 42 bits and has a format shown in the opposite page. The Decimator outputs one out of every 64 bits of the long code so that the output rate is reduced to 19.2 kbps.

The paging channel DOES NOT carry power control subchannels.


Issue II Rev 4

The Paging Channel

• Operates at 9600 0r 4800 bps speed. • Used by base station to convey system overhead info and mobile specific

messages to the mobile. • Does not carry power control sub channels.

Use the same PN sequence offset as the pilot channel. • • Up to 7 Paging channels are possible, the first one taking Walsh code number

W1.

ConvolutionCoderr=1/2;K=9

Symbolrepetition

Block Interleaver

WalshCode , W1- w7

PN chips1.2288 Mbps

A9600 bps4800 bps

Code Msymbol

odsymbol

19200 or9600bps

19.2ksps

Modsymbol19.2ksps

+

Long Code Maskfor paging chl. P Long code

generatorDecimator64:1

19.2 ksps

Quadrature spreading circuitry

A s(t)

Paging Channel Arrangement:

Paging Channel Long Code Mask 41 29 28 24 23 21 20 9 8 0

1100011001101 00000 PCN 000000000000 PILOT_PN

PCN - Paging Channel numberPILOT_PN - Pilot PN sequence offset index for the forward CDMA Channel.


Issue II Rev 4

Paging Channel Structure

_________________________________________________________ The Paging channel Structure

The paging channel is used for sending control information to mobiles which are not assigned to a traffic channel; i.e., to mobiles which are not engaged in a call. We have earlier seen the characteristics of the paging channel and a block schematic of how it is implemented. Let us now look at the actual structure of the Paging Channel, as we did for the Sync Channel. The paging channel structure is shown in the opposite page.

• The paging Channel is sent in 80 ms SLOTS. • A maximum of 2048 slots (numbered 0 to 2047) are possible. The

grouping of 2048 paging slots is called the “Maximum Slot cycle ”. The cycle duration is 163.84 seconds.

• A mobile, operating in the slotted mode monitors the paging channel using a slot cycle which is a sub multiple of the maximum slot cycle length.

• Each 80 ms slot is divided into 4 sub frames of 20 ms. • Each 20 ms sub frame is divided into two 10 ms halves. The first

bit in any such half frame is the SYNCHRONIZED CAPSULE INDICATOR (SCI) bit.

• Just like the sync channel, a paging channel message capsule consists of a message body, padding bits and CRC.

• The base station may send either a synchronized paging message capsule or an unsynchronized one. The former begins immediately after the SCI bit whereas the latter starts immediately AFTER the previous message capsule.

• If there are 8 or more bits available BEFORE the next SCI is due, the base station may send an unsynchronized message capsule immediately following the paging message. No padding bits are added in such cases.

• If there are less than 8 bits before the next SCI, or, if NO unsynchronized message is sent, the base station adds padding bits up to the position of the SCI bit.

• The base station sets the SCI bit to ‘1’ for synchronous messages and it is set to ‘0’ in all other cases.

• The FIRST paging message to be sent on any paging channel is a synchronized message capsule. This permits mobiles operating in the slotted mode to achieve synchronization immediately after becoming active.


Issue II Rev 4

The Paging channel Structure • Divided into 80 ms slots. Maximum 2048 slots. • Each 80 msec slot is divided into four 20 ms sub frames. • Every 20 ms slot is divided into two 10 ms half frames. The first bit of each half

frame is called the Synchronization Capsule Indicator (SCI) • Synchronized messages are immediately preceded by the SCI. The

unsynchronized messages follow the current message. • If there are less than 8 bits before the next SCI is due, padding bits are added.

If there are more than 8 bits then the base station sends an unsynchronized message without any padding bits.

• The first paging message in any paging channel is a synchronized message capsule.

163.84 sec; 163.84 x R bits ; R = 9600 or 4800 bps.Maximum Paging Channel Slot cycle ( 2048 slots )

80 msec ; .08 x R bits

slot 0 slot 1 slot 2 slot 2047.......................

4 frames of 20 msec; Two 10 msec half frames per frame.10 msec; .01 x R bits

Paging ChlHalf Frame




SC I

SC I

SC I

SC I

Half framebody

Half framebody

Half framebody

Half framebody

0 1 0 1

paging chl capsule paging chl capsule paging chl capsule paging chl capsule

. . . . . . . . . . . . .

First PagingcapsuleSynchronous

AsynchronousCapsules

AsynchronousCapsules

SynchronousCapsule

MSG_LENGTH MESSAGE BODY CRC PADDINGBITS

. . . . . . . . .. . .


Issue II Rev 4

The Table in the opposite page shows the different types of Paging Channel messages. The messages are grouped as shown in the table and are sent either periodically or on an as- required basis.

The Paging Channel Messages ______________________________________________________ Paging Channel Messages


Issue II Rev 4

Paging channel Messages

Message Name Message type ( binary )

Remarks Systems Parameters 00000001 A number of fixed length messages are sent i

this group. see Table 2. Access Parameters 00000010 defines the parameters to be used by a

mobile while on an Access channel; it is a variable length message.

Neighbour List 00000011 This is a variable length message. CDMA channel list 00000100 - do - Slotted Page 00000101 - do - Page Message 00000110 - do - Order Message 00000111 Orders are sent to the mobile by the base

station for base stn ack., pilot measurement request, registration accepted, message encryption mode etc. This is a variable length message.

Channel Assignment 00001000 A variable length message Data Burst Message 00001001 - do - Authentication Challenge 00001010 This is a FIXED length message SSD update 00001011 - do - Feature Notification 00001100 This is a variable length message Extended system Parameters

00001101 - do -

reserved 00001110 reserved 00001111 service Redirection 00010000 This is a variable length message General Page 00010001 - do - Global service redirection 00010010 - do - Null message ------------- Fixed length message format


Issue II Rev 4

Paging Channel Messages Types

_________________________________________________________ Paging channel Message types - System Parameter Messages

The system parameter messages are a group of fixed length messages sent on the Paging channel by the base station. There are, in all, 41 different types of system parameter messages. Table given in the opposite page shows some of the important message types.


Issue II Rev 4

System Parameter Messages

Field Len ( bits ) Remarks MES_TYPE 8 SET TO “00000001”. PILOT_PN 9 pilot PN offset for the base station, in units of 64 PN chips. BASE_ID 16 Base station identification number PAGE_CHAN 3 sets the number of paging channels POWER_UP_REG 1 To enable mobiles to register immediately after powering on

and receiving the system over head messages. ‘1’ enables the facility and a ‘0’ disables it.

POWER_DOWN_REG 1 To enable a mobile to register immediately before powering off.

REG_PER 7 Registration period. For non roamer based registration, the value is set to ‘0000000’. The base station sets the field to any value within 29-85, In case the mobile does timer based registration. The timer value is given by: T ( integer) = 2REG_PER/ 4 x .08 sec.

PWR_REP_THRESH 5 The power control reporting threshold. PWR_REP_FRAMES 4 Power control reporting frame count. The base station sets

this number which decides the number of frames over which the mobile should count frame errors. The number is given by the integer value of 2(PWR_REP_FRAMES/ 2) x 5 frames.

PWR_PERIOD_ENABLE 1 Set to ‘1’ if the mobile is to send periodic measurement reports.

PWR_REP_DELAY 5 Sets the period for which the mobile waits following a Measurement report message before restarting frame counting for power control purposes. The value should be in multiples of 4 frames.

T_ADD 6 Pilot detection threshold. Triggers transmission of Pilot strength measurement message, initiating a hand off process.


Issue II Rev 4

The Forward Traffic Channel _______________________________________________________ The Forward Traffic Channel

The forward traffic channel operates at variable speeds upto 9600 bps. With one pilot channel, one sync channel and seven paging channels, we could have a maximum of 55 traffic channels. The block schematic of the traffic channel is shown in the opposite page. The arrangement is more or less similar to the reverse channel. The signals are passed through a convolutional encoder of r=1/2 and constraint length K=9. For every input bit, we get two bits at the output. The symbol repeater after the convolutional coder repeats the symbols twice for 4800 bps speed, 4 times for 2400 bps and 8 times at 1200 bps.

The block interleaver has specific write and read sequences/patterns for different speeds of operation. The details of read - write arrays are not included in the manual. The output of the interleaver is scrambled using a 64:1 decimator. The scrambling is done by modulo-2 addition of the interleaver output with the binary value of the long code chip which is valid at the beginning of transmission period for that particular symbol. The resulting PN sequence is the same as the long code at 1.2288 MHz clock rate where only the first output of every 64 bits is used for scrambling the data.

The scrambled data (19.2 kbps) is then passed through a Multiplexer where the power control bits are added. For scrambling the power control bits, the output of the 64:1 decimator is passed through another decimator to produce a bit rate of 800 bps.

The multiplexer output is then subjected to orthogonal modulation by Walsh codes and then are quadrature spread. The Walsh code table is the same as in the case of the reverse channel. The major difference is that in the forward channel, the 64 bit Walsh code is sent for every code symbol where as in the reverse channel the Walsh code is sent for every 6 symbols.

Note

The forward link uses the Walsh Codes to provide orthogonality between logical channels within a cell or sector.

The reverse channel uses the same set of Walsh Codes for isolating six bit blocks of data transmitted by the mobile.

The multiplex options for primary and secondary traffic/ signalling are the same as for the reverse channels.


Issue II Rev 4

The Forward Traffic Channel

+ +

Forward Tfc chlinfo bits(172/80/40/16bits / frame




19.2 kbps 9.6 kbps 4.8 kbps 2.4 kbps

19.2 kbps

19.2 kbps

19.2 kbps

19.2 kbps

19.2 kbps

Add FrameQualityIndicators

Add 8 bitencoder tail

Convolutioncoderr=1/2; K=9

symbol repetition

Block Interleaver

MUX

Long CodeMask Long Code

Generator64:1Decimator

24:1Decimator

800bps

Walshcode n1.2288Mcps

A*

pwr cont800 bits

* ‘A’ is the quadrature spreading circuitry.


Issue II Rev 4

Forward Channel-Power Control Sub Channel _______________________________________________________ Forward Traffic Channel- Power Control sub channel

Before discussing the functions of the Power Control Sub channel in the forward link, let us understand the mechanism of Power Control in CDMA. There are basically 2 methods of power control in CDMA:

Open Loop Power Control

This is purely a mobile unit function. It gives open estimation. This is done only during the initial stage as soon as the mobile is turned ON.

Closed Loop Power Control

This involves both the base station and the mobile unit and gives a closed loop power correction.

The power correction is done on the forward channel.

Output Power Limits

Before we understand the concepts of power control in CDMA, we need to look at the output power limits for the mobile. In earlier sections we come to know that the mean output power of the mobile should be less than - 50 dBm / 1.23 MHz, for all frequencies within ± 615 kHz of the centre frequency. Further, the mobile transmits nominal power only during gated- ON periods of 1.25 ms; the 1.25 ms durations are called power control groups. The output is defined in a power mask shown opposite:


Issue II Rev 4

Output Power Limits

20 dB or to theNoise Floor

6 microseconds

3 dB

1.25 mSec

Mean output powerof the ensembleaverage.( reference line

Transmission Envelope Mask - Average Gated-on Power Control Group


Issue II Rev 4

Power Control

_________________________________________________________ Power Control

Implementing power control for the reverse link helps eliminate or minimize what is called a “ Near - Far ” interference problem. This is explained in detail later in the section.

The idea is to control the output of all the mobiles in a cell such that the total power received at a cell site from all the mobiles is equal to the nominal receive power level times the number of such mobiles.

i.e., [ Prec ]FROM ALL MOBILES = [ PREC ]PER MOBILE X number of mobiles

Effect of Power control

The signal received by a mobile is subject to both log normal and Raleigh fading as shown in Fig.(a). The average path loss is obtained from this. If the receive signal power could be REVERSED as shown in fig. (b), then it would nullify the power variations at the cell site, i.e., the base station.

At the cell site, the receive signal quality is examined with reference to the available Frame Error Rate and the EXPECTED value of FER. Then a decision on whether a mobile needs to increase or decrease its output power is taken. This mechanism is called the CDMA closed Loop Power Control. The mobile power RECEIVED at the cell site after closed loop control looks like as shown in Fig.(c).


Issue II Rev 4

Power Control Mechanism

MS rec.sig.strengthRayleigh Fading

Avg. Path Loss

DistanceMS Tx Pwr w/o closed loop

Tx Pwr w/o smooth filter

desired avg Tx power

Fig. ( a ). Mobile Rec. signal in log normal & Rayleigh Fading

Fig. ( b ). Mobile Transmit Power Without closed loopcontrol


Mobile rec.powerat Cell site

Distance

Receive Power at Cell sitewith closed loop control

Fig. ( c ). Mobile Power at cell site, with closed loop control.

Issue II Rev 4

Open Loop Power Control

_________________________________________________________ Estimated Open Loop Power

When the mobile is turned ON, it is in what is called the ACCESS STATE and looks at the Pilot, Synchronization and the Paging Channels coming from the base station. The Paging channel contains a number of Access Parameters which the mobile should be using.

In the Access State, the mobile is not assigned any traffic channel and therefore the closed loop corrections will not be active.

The mobile starts by sending a weak signal, if Pilot signal from the base station is strong. (This means that the mobile is quite close to the base station and in CDMA the basic aim is to transmit just the minimum power required for a specified quality or performance objective; transmission of more power would make the mobile a ‘ jammer’ for all other mobiles. If the pilot signal from the base station is weak, then the mobile transmits a higher power. To put it differently, the mobile transmit power is inversely proportional to the Pilot level it receives from the base station.

The mobile transmits its FIRST access signal (called the Access Probe ) at a nominal power level defined by the following equation:

Mean output Pwr (dBm.) = - Rec. Pwr (dBms) - 73 + NOM_PWR + INIT_PWR + the sum of access probe corrections. where, INIT_PWR is the adjustment to the first probe to make it less than the desired signal power. Its range is -16 to 15 dB, and its nominal value is 0 dB. NOM_PWR is the correction that is required to provide the correct receive power at the base station. The range is - 8 to 7 dB and nominal value is 0 dB.

For the FIRST access probe, the corrections are zero. When the base station does not respond to the first probe from the mobile, the latter sends another probe by incrementing its transmit power by a PWR_STEP. This has a range of 0 to 7 dB. The incrementing or decrementing the power is called the Access Probe correction. For example, without any corrections or adjustments, Mean Output Power = - Rec.Pwr - 73 = - ( -90 dBm ) - 73 = + 17 dBm. The values of NOM_PWR, PWR_INIT and PWR_STEP are all assumed to be 0 dB.


Issue II Rev 4

Estimated Open Loop Power Control

• When the mobile is turned ON, it locks on to the pilot, paging and sync channels.

• There is no traffic channel assigned to the mobile and hence there is no closed loop power control.

• The mobile Tx power during this initial Access state is inversely proportional to the Pilot signal strength received from the base station.

•

• If the base station doesn’t respond for the first probe, the mobile increments its output by a PWR_STEP, within a range of 0-7 dB.

The FIRST access probe is sent at a nominal power given by: (PT)mob = - ( Prx ) - 73 +NOM_PWR + INIT_PWR

Where • INIT_PWR is the adjustment to the first probe to make it less than

the desired signal power. Its range is -16 to 15 dB, and its nominal value is 0 dB.

• NOM_PWR is the correction that is required to provide the correct receive power at the base station. The range is -8 to 7 dB and nominal value is 0 dB.

• For example, if the nominal receive level is -90 dBm, ten the mobile TX power for the first probe without any corrections is +17 dBm.

• After a traffic channel is assigned to a mobile, the power control shifts to the Closed loop mode.


time

Tx Power

First Access power.

= - PR - 73 + NOM_PWR + INIT_PWR

One PWR_STEP

Base station ACK Time out Random Time out before thenext probe

Bangalore, India

Issue II Rev 4

Near-Far Problem in the Reverse Link

_________________________________________________________ Power Control

Earlier we mentioned that the idea behind power control is to control the output of all the mobiles in a cell such that the total power received at a cell site from all the mobiles is equal to the nominal receive power level times the number of such mobiles.

i.e., [ Prec ]FROM ALL MOBILES = [ PREC ]PER MOBILE X NUMBER OF MOBILES.

This means that on the reverse link we ensure that all mobiles cause the same receive level at the base site. On the forward link, the purpose of power control is to limit the Tx. power of the base station in respect of individual mobiles such that the mobiles receive more or less at the same level; this would ensure that there is minimum interference on the mobile receive paths.

So, the fundamental idea is to keep the receive levels at a specified constant value, irrespective of the distance of the mobile from the base station. This is required to solve what is called the “ Near-Far” problem.

Near - Far Problem in the Reverse Link

This is illustrated in the Diagram opposite. If the mobiles M1 and M2 transmit at the same output power levels, then, if both the mobiles are at the same distance ‘d’ from the base station, then we may assume the receive levels for these mobiles at the base station would be the same.

i.e., ( PR1 )due to mob.1 = ( PR2 )due to mob.2

If mobile 1 is the desired mobile, then the signal coming from mobile 2 is the interference signal. Since both are of equal power, the C/I in this case will be 1. [Fig. (a)] Now, if mobile 2 moves to a point d/2 from the base station, then the receive level at the base station would increase by 16 times. This is because, in the mobile environment, the receive power varies inversely proportional to the 4th power of distance. This means that the C/I becomes 1/16 i.e., the C / I has become poorer. However, if we assume 16 mobiles at the same distance d (as for mobile 1), then the receive signal at the base station would be 16 times the receive level caused by one mobile. If the over all C /I is acceptable, then the capacity of the system increases by 16 times (theoretically).


Issue II Rev 4

Near - Far Problem (Reverse Channel)

d

M1

M2

PT

PT

PR2

PR1

PR1 PR2=C / I = 1.

Fig. ( a ). Receive signals at the base station; 2 mobiles at the same distance.

d

M1

M2

PT

PT

PR2

PR1

PR2 16 PR1=C / I = 1 / 16.

Fig. ( b ). Receive signals at the base station; 2 mobiles at different distances

timed / 2


Issue II Rev 4

Near-Far Problem - Forward Link

_________________________________________________________

Near - Far Problem in the Forward Link

Remember that the base station transmits signals to a number of mobiles simultaneously, using the CDMA technique. This means that the total power transmitted by the base station is the sum of trans. power for all the forward channels in use at the given instant of time. Imagine that the base station transmits to 2 mobiles at the same distance from it. The trans. power resources used by the base station for either of the mobiles is the same, say PT. The signals arriving at the mobiles would be equal in strength and the C/I would be =1.

Suppose mobile M2 moves closer to the base station, to a point d/2 from it. Assuming that the base station still transmits at the same power, the signal strength at M2 would be 16 times stronger than that at M1. (1/d4 model).

This means that the closer mobile will have a better C/I (16 in this case) and those far away from the base station will have poorer C/I values. More over the high receive levels act as jammers to other mobiles

Therefore the power control strategy is to allocate lower power resources to mobiles which are close by and higher resources to mobiles that are farther away.

The mobile measures the FER of the received signal and sends a Power Measurement Report Message to the BTS if the FER crosses a specified limit. The BTS does the Forward Link Power Control adjusting the power gains of the forward link Traffic channels.


Issue II Rev 4

Near - Far Problem (Forward Link)

M1

M2

PT

(PR)1

(PR)2

PR1 = PR2

C / I = 1.

d

Fig. (a ). Base Station sending constant Power to mobiles at the same distance

M 1

M 2

P T

(P R)1

(P R )2

P R 2 = 16 P R 1

d

F ig . (b ). B ase S ta tio n T ran sm ittin g to 2 m o b iles a t d iffe ren t p o in ts

d / 2

tim e


Issue II Rev 4


_________________________________________________________


Closed Loop Power Control is done by using the Power Control Groups in the Traffic Channels.

Power Control Groups in Reverse Channels

The reverse traffic channels are transmitted in 20 ms frames. Each reverse traffic channel frame is divided into 16 slots of 1.25 ms each. Each slot is called a Power Control Group.

One Frame consists of 192 bits.

One Power Control Group Consists of 12 bits. With rate 1/3 Convolutional coding, we get 36 Code Symbols.

For 6 bits we have one Modulation Symbol and hence a Power Control Group will have 6 Modulation Symbols.

The duty cycle of the transmission gate varies with the trans. data rate.

For a full rate frame (data rate 9600 bps).............16 Power Groups For a half rate frame (data rate 4800 bps)............. 8 Power Groups For a 1/4th rate frame (data rate 2400 bps)...........4 Power Groups For a 1/8th rate frame (data rate 1200 bps)...........2 Power Groups


Issue II Rev 4

0 1 15

20 msecs1.25 msec

192 bits


Issue II Rev 4

Forward Channel- Power Control Sub Channel

_________________________________________________________ Forward channel- Power Control Sub Channel

The block schematic of the Forward channel is reproduced in the opposite page. The focus is the output of the interleaver and the input to the MUX.

800 Power Control bits are sent per second over a number of 20 ms forward channel frames. This means we can transmit 1 bit every 1.25 ms. This corresponds to the duration of one power control group in the reverse channel.

The base station monitors the receive signal strength of a mobile over 1.25 ms. Based on the receive signal strength, the base station sends a power control bit over the forward traffic channel, through the power control sub channel.

The power control information is sent continuously at a rate of ONE BIT every 1.25 ms. This gives a bit rate of 800 bps.

A ‘0’ bit indicates that the mobile should INCREASE its output power and a ‘1’ indicates it should DECREASE the output.

The power adjustments are done for every power control bit transmitted.


Issue II Rev 4

Forward Channel - Power Control sub channel

• 800 bits per second • Sent over 20 ms frames • One bit every 1.25 ms • Power Control bits are added to appropriate Power Control groups. • ‘1’ means Power should be stepped down and ‘0’ means it should be

stepped up. • Power Control for the Reverse Channel is done through the Forward

channel- power control sub channel.

+ +

Forward Tfc chlinfo bits(172/80/40/16bits / frame




19.2 kbps 9.6 kbps 4.8 kbps 2.4 kbps

19.2 kbps

19.2 kbps

19.2 kbps

19.2 kbps

19.2 kbps

Add FrameQualityIndicators

Add 8 bitencoder tail

Convolutioncoderr=1/2; K=9

symbol repetition

Block Interleaver

MUX

Long CodeMask Long Code

Generator64:1Decimator

24:1Decimator

800bps

Walshcode n1.2288Mcps

A*

pwr cont800 bits

* ‘A’ is the quadrature spreading circuitry.


Issue II Rev 4

Forward Channel-Power Control Sub Channel

_________________________________________________________

Forward Channel - Power Control Sub Channel

The power control bit on the forward channel is sent on the SECOND power control group following the corresponding group on the reverse channel in which the signal strength was estimated by the base station. For instance, if the receive signal was estimated in power control group number 10 in the reverse channel, then the power control bit is sent on power control group number 12 in the forward channel.

The duration of a power control bit is 104.1666 µSec which is exactly twice the duration of a modulation symbol. The power control bit replaces 2 consecutive modulation symbols on the forward traffic channel. This method of replacing a traffic channel symbol for a power contra bit is called “SYMBOL PUNCTURING” technique.

There are 16 possible starting positions for the power control bit. each position represents one of the first 16 modulation symbols ( numbered 0 to 15 ) of a 1.25 ms period. In each of such 1.25 ms periods, a total of 24 bits are used in the long code for scrambling purposes. These bits are numbered 0 to 23 and bit 0 is used first and bit 23 last.

The decimal equivalent of bits 23,22,21,20 decide the position of the power control bit.

In the diagram opposite, the value of these 4 bits is 10 and the power control bit starts at the 10th position.


Issue II Rev 4

Power Control Sub Channel

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 11 12 13 1510 14

0 1 2 3 4 5 6 7 8 9 11 12 13 1510 14 16 17 ......... 2320 21 22 23

1 0 1 0

Base station measures rec.signal strength and sendspower control bit.

20 msec = 96 mod sym = 16 Power Control Groups

1.25 msecReverseTraffic

ForwardTrafficchannel

Lusedscrambl

Last 4 bitsof the 24:1Decimator

channel

ong code bits for

ing

16 possible starting positions for thepower control bits.

value=10; position ofpwr control bit

Power control bit2 mod. symbols transmitted

1.25 msec = 24 modulation symbols ( 192x2/ 16)

• The base station estimates receive signal strength and sends power control bit on the power control sub channel in the forward traffic channel.

• ‘0’ means mobile should INCREASE its power and ‘1’ means it should DECREASE its output power.

• The power control bit is sent in the 1.25 msec power control group. If the receive signal strength is measured in power group number ‘x’ in the reverse channel, the control bit is sent on the power control group number ‘x+2’ on the forward channel.

• The power control bits are scrambled using a 24:1 decimator to get a rate of 800 bps.

• Value of bits 20-23 of the decimator o/p are used to decide the position of the power control bit in the sub group.


Issue II Rev 4

System Timing Aspects

_________________________________________________________

System Timing Aspects

After studying the basic formats of both the Forward and the Reverse Channels, let us now look at how the system timings are handled in CDMA.

CDMA System Time

All base station emissions are referenced to a common system time scale which itself uses the GPS time scale. The GPS time scale is synchronized to another time scale called the “ Universal Coordinated Time”( UTC). The GPS and UTC differ by an integer number of seconds.

The start of the GPS / CDMA time scale is 6th Jan 1980 00:00:00 UTC

The diagram opposite shows the relation of System Time at various points in the CDMA system. The long code and the zero offset pilot PN sequences are shown at the start of the system time. The initial state of the long code is that state in which the output of the long code generator is the first ‘1’ after 41 consecutive ‘0’s.

The precise zero instant of the System Time is the mid point between the last ‘0’’ of 41 consecutive ‘0’s and the succeeding ‘1’ of the long code generator.

It has been estimated that the second time alignment of the initial states of the long code and the pilot PN sequences will not take place for more than 37 CENTURIES !!

The system time is the absolute time referenced at the base station antenna offset by the one way or round trip delay of transmission, as appropriate. Time measurements are referenced to the transmit and receive antennas of the base station and the RF connector of the hand set. The System Time is referred to in frames and is equal to an integer value of s/.02 seconds where ‘s’ is the system time in seconds.


Issue II Rev 4

CDMA SYSTEM TIME

• Referenced to GPS time scale. • Start of the System Time is 6 Jan 1980 00:00:00 • The initial states of long code and pilot PN sequences coincide with the start

of the system time. • Second time coincidence does not occur before 37 centuries!!

CDMA SYSTEM TIME REFERENCES


BaseTX

BaseRX

MobileRx

MobileTx

Jan

6 19

80 0

0:00

:00

UTC

Jan

6 19

80 0

0:00

:00

UTC

Jan

6 19

80 0

0:00

:00

UTC

‘...1 0(41) ‘1...’‘...1 0(15) ‘1...’‘...1 0(15) ‘1...’

‘...1 0(41) ‘1...’‘...1 0(15) ‘1...’‘...1 0(15) ‘1...’

‘...1 0(41) ‘1...’‘...1 0(15) ‘1...’‘...1 0(15) ‘1...’

‘...1 0(41) ‘1...’‘...1 0(15) ‘1...’‘...1 0(15) ‘1...’

Long code Mask = ‘1 041 ’Zero offset I pilot PN seqZero offset Q pilot PN seq

Long code Mask = ‘1 041 ’

Zero offset Q pilot PN seqZero offset I pilot PN seq





One way delay3 micro sec/km

0 (n) meansn consecutivezeros

Issue II Rev 4

Section 7

CALL PROCESSING


Issue II Rev 4

Section 7 Call Processing 168 Objectives 170 Call Processing in CDMA 171 Acknowledgement Procedures 175 Mobile Station-Initialization state 177 Pilot Acquisition-Sub state 179 Sync Channel Acquisition-Sub state 181 Timing change substate 183 Mobile station idle state 185 Paging channel monitoring 187 System access state 189 Access Procedures 191 Mobile Station on traffic channel 195 Registration 197 Roaming 199 Authentication 201 Handoff procedures 209 Pilot sets 211 Pilot Strength –measurements 217 Handoff procedures – flow chart 219 Handoff threshold comparisons 221 Call Processing cases 223


Issue II Rev 4

Objectives

_________________________________________________________ Objectives


List the 4 different basic “ States ” of a mobile in the CDMA environment. Explain the basic “ Acknowledgment Procedures ” in CDMA. List some of the important parameters used in CDMA Call

Processing. Explain with simple diagrams, the various “substates” of the

mobile. Explain the “ Access Procedures ” in CDMA. Explain “ Registration Procedures ” in CDMA. Explain how “Authentication” is performed in CDMA. Define “Hard” and “Soft” hand-offs in CDMA. List the types of Pilot Sets in CDMA and explain the significance

of each. Explain hand-off procedures in CDMA. Explain with simple signal flow diagrams, the various Call

processing steps in CDMA.


Issue II Rev 4

Call Processing in CDMA

_________________________________________________________ Basic Operational States

Basically, the mobile station call processing involves 4 different states, as shown in the diagram opposite.

MOBILE STATION INITIALIZATION STATE

The mobile enters this state when it is powered ON. During this state, the mobile selects and acquires a system. In a mixed environment where both analog and CDMA are available, a choice is made between the two during the initialization state.

The initialization state itself has 4 states. We will look at these later in this section.

MOBILE STATION IDLE STATE

During this state, the mobile station monitors the messages on the PAGING channel.

SYSTEM ACCESS STATE

In this state, the mobile communicates with the base station and exchanges information on the ACCESS channel.

MOBILE STATION CONTROL ON THE TRAFFIC CHANNEL

This is the conversation stage when the mobile and the base station communicate on the forward and reverse traffic channels.


Issue II Rev 4

Call Processing in CDMA Basic States

• Mobile station Initialization State • Mobile station idle State • System Access State • Mobile Station Control on the Traffic Channel State

P o w er O N

In itia lis a tio n S ta te

Id le S ta te

S y s te m A c c e s s S ta te

M o b ile S ta tio n c o n tro lo n th e T ra ffic C h a n n e l

G ets th e p ilo tch a n n e l an d acq u ires th e sys tem .

M o n ito rs th e P a g in g ch an n e l.

T a lks to b a se -s ta tio n o n th e A cce ss ch an n e l

R e sp o n d s to a P ag e o rin itia te s a ca ll

G e ts a tra ffic ch a n n e l a llo tted .

C o n versa tio nsta te .

R e tu rn s to in titia lisa tio n s ta te a fte r co n v ersa tio n


Issue II Rev 4

Call Processing in CDMA

_________________________________________________________

•

•

•

•

•

•

This specifies the ACK sequence number. This is equal to the MSG_SEQ number.

Some Important Parameters

Some of the important parameters/message types used as the mobile goes from one state to another are given below. The messages / parameters are:

Stored in the mobile’s temporary memory < parameter >s OR

Stored as a variable value that changes from time to time < parameter >sv

OR Stored within specified limits on values that vary < parameter >sl

OR Indicative of a value received by the mobile < parameter >r

OR Stored permanently in the mobile < parameter >p

OR Stored in semipermanent memory of the mobile < parameter >s-p

Common Fields For proper interaction between the mobile and the base station, certain Acknowledgment procedures are followed, whether the mobile is in Access channel or Paging channel or Traffic channel. In all such Acknowledgment procedures, the mobile uses certain common fields in its data format. ACK_TYPE

This defines the Acknowledgment address type. This is related to the Address_Type. Each of the states has some messages. For example, the Paging channel has System Parameters. When a message is sent under this category, the Address type is for System Parameters. The ACK_Type then corresponds to this category.

ACK_SEQ

MSG_SEQ This specifies the Message Sequence Number

ACK_REQ This means an acknowledgment is required; ‘1’ means ACK required to be sent to the base station. This field is included in the message coming FROM the base station.

VALID_ACK ‘0’ means message doesn’t include an Ack to the base station.

These fields are layer 2 fields and the ACK procedures are called Layer 2 Procedures.


Issue II Rev 4

Common fields

• Call processing involves certain acknowledgment procedures between the mobile and the base station.

• The base station message has certain fields which control the ACK procedures.

• ADDRESS_TYPE: Specifies the type of Address.

• ACK_TYPE:Mobile sets this field while responding. Equals

ADDRESS_TYPE.

• MSG_SEQ: Message Seq. Number, sent by base station

• ACK_SEQ: Set by mobile while responding; equals MSG_SEQ.

• ACK_REQ: Base station indicates if an ACK is required for a particular message.

• VALID_ACK: Set to ‘1’ by mobile in its response if an ACK was asked by

the base station. After sending the ACK, the mobile does not set this field UNTIL it receives another message from the base station that requires an ACK.


Issue II Rev 4

Acknowledgement Procedures

_________________________________________________________ Acknowledgment Procedures

Based on the common fields defined in the previous page, the base station and the mobile interact, in general, as per the procedure outlined below:

• A message coming from the base station will have: # The Address Type ( say, System Parameter Message ) # Whether ACK is required # Message sequence number # Other data fields.

• If the base station wants an acknowledgment, it would set the

ACK_REQ field. The mobile then sends an acknowledgment along with:

# Valid -ACK field set to ‘1’ # ACK-TYPE field set to address type of message being acknowledged. # ACK-SEQ field set to MSG-SEQ number of message being acknowledged.

• If the base does not want an acknowledgment, then the mobile verifies if the message received by it was a Paging Message. If yes, it then sends a Paging Response Message, by setting the Valid-ACK, ACK-TYPE and ACK-SEQ fields as mentioned above.

• If the message was not a Paging channel message, then, the mobile verifies if the previous message received by it needed an ACK.

• If the previous message needed an ACK, then the mobile sets the Valid-ACK field to ‘0’.

• If the previous message did not require an ACK, then the mobile sets the common fields as follows:

# Valid-ACK field ‘0’ # ACK-TYPE field ‘000’ # ACK-SEQ field ‘111’.

• The MSG-SEQ number for a message is INCREMENTED ONLY WHEN the contents of the message changes. For example, if the base station pages a mobile repeatedly, then the message sequence number remains the same.

The foregoing is illustrated as a flow chart in the diagram opposite. Some of the important parameters are given Appendix.


Issue II Rev 4

Acknowledgment Procedures

Other data fields Address Type ACK-REQ MSG-SEQ number

= 1 ?

Paging ?

Didprevious message

need an ACK ?

Yes

Yes

Yes

No

No

No

Message from the Base station

same as “A”

Valid-ACK : ‘1’ACK-TYPE: address typeACK-SEQ: MSG-SEQ number

“A”

Valid-ACK: ‘0’ACK-TYPE: Address type of last message requiring an ACKACK-SEQ: MSG-SEQ number of last message requiring an ACK.

Valid-ACK: ‘0’ACK-TYPE: ‘000’ACK-SEQ: ‘111’


Issue II Rev 4

Mobile Station – Initialization State

_________________________________________________________


This State consists of 4 sub states. In this state the mobile selects a system to use. If the selected system is CDMA, then the mobile tries to synchronize with the CDMA system. The 4 sub states are:

• System Determination Substate • Pilot channel Acquisition sub state • Sync Channel Acquisition sub state • Timing change sub state.

System Determination Sub state

In this sub state, the mobile- •

• If the mobile selects the CDMA system, then it sets the parameter CDMACHS to an appropriate CDMA channel number.

Determines the appropriate system to use. Choices are between operators and between CDMA and Analog mobile systems.

• After this the mobile enters the Pilot acquisition sub state.


Issue II Rev 4


• This State consists of 4 sub states: ⇒ System Determination Substate ⇒ Pilot channel Acquisition sub state ⇒ Sync Channel Acquisition sub state ⇒ Timing change sub state.

• System Determination Sub state: In this sub state, the mobile-

⇒ Determines the appropriate system to use. Choices are between operators and between CDMA and Analog mobile systems.

⇒ If the mobile selects the CDMA system, then it sets the parameter CDMACHS to an appropriate CDMA channel number.

⇒ After this the mobile enters the Pilot acquisition sub state.

Power ON

Network Operator A Network Operator B

C D M A System Analog System

F1 FJ FN

Note: F1 to FN are CDMACHS numbers.


Issue II Rev 4

Pilot Acquisition – Sub State

_________________________________________________________ Pilot Acquisition Sub state

In this state, the mobile acquires the pilot channel.

•

o

o o

Upon entering the Pilot Acquisition sub state, the mobile Tunes to the CDMACHS.

o Sets its code channel to the Pilot channel. Searches for the Pilot. (signal consists of “all ‘0’s ”) If it acquires Pilot within a specified time limit (T20M), the mobile enters the Sync Channel Acquisition sub state.

o Otherwise, it RETURNS to the System Determination Substate with an Acquisition failure indication.

If the PN offset of the CDMACH selected is TJ , TP is the propagation Delay, then we say that the Pilot Acquisition occurs when the delay T of the locally generated PN sequence (in the receiver) EQUALS the total delay (TJ + TP).

Note: In the diagram opposite, T20m is the maximum time to remain in the Pilot Acquisition state and is equal to 15 seconds.


Issue II Rev 4

Pilot Acquisition Sub state In this state, the mobile acquires the pilot channel.

• ⇒

⇒ ⇒

Upon entering the Pilot Acquisition sub state, the mobile: Tunes to the CDMACHS.

⇒ Sets its code channel to the Pilot channel. Searches for the Pilot. ( signal consists of “all ‘0’s ” ) If it acquires Pilot within a specified time limit ( T20M), the mobile enters the Sync Channel Acquisition sub state. Otherwise, it RETURNS to the System Determination Substate with an Acquisition failure indication.Pilot Acquisition occurs when the delay T of the locally generated PN sequence ( in the receiver ) EQUALS the total delay ( TJ + TP ).

Power ON

sys.determine

set CDMACH

set Code chl

search Pilot

Pilot gotwithin T20m ?

Yes No

Sync channel Acquisition State

CDMA chl number = CDMACHS

T20m = 15 seconds


Issue II Rev 4

Sync Channel Acquisition – Sub State

•

•

• • • • • • •

_________________________________________________________ Sync channel Acquisition Sub state

In this substate, the mobile gets the system configuration and timing information by processing the sync channel messages.

If the sync channel acquisition is successful, then the mobile enters the next substate- i.e., the timing change sub state.

If the sync acquisition is not correctly done then the mobile RETURNS t the System Determination substate.

The following rules are applied

The mobile returns to system determination substate... if....

The mobile does not receive a valid Sync message within a specific time out period (defined by T21m) or, The mobile receives a valid sync message but the Protocol revision level supported by the mobile [MOB_P_REVP] is LESS than the minimum level supported by the base stain [MIN_P_REVr]

If the mobile receives the sync message properly and MOB_P_REVP is GREATER than MIN_P_REVr , the mobile stores the following info from the sync message:

P_REVS = P_REVr MIN_P_REVS = MIN_P_REVr SIDS = SIDr NIDS = NIDr PILOT_PNs = PILOT_PNr SYS_TIMES = SYS_TIMEr PRATS = PRATr

Mobile would ignore any other fields coming at the end of the message which are not defined according to MOB_P_REVP, stored permanently in the handset.

Note: In the diagram opposite, T21m is the maximum time to receive a valid Sync channel message and is equal to 1 second.


Issue II Rev 4

Sync Channel Acquisition Substate

Power ON

System Dtermine

Pilot Acquisition

Sync Acquisition

< T21m ?yes no

MOB_P_REVless thanMIN_P_REV ?

no yes

Timing change state

The mobile stores the followingif sync aquisition is successful:

• P_REVS = P_REVr• MIN_P_REVS = MIN_P_REVr• SIDS = SIDr• NIDS = NIDr• PILOT_PNs = PILOT_PNr• SYS_TIMES = SYS_TIMEr• PRATS = PRATr

T21m = 1 second


Issue II Rev 4

Timing Change Substate

_________________________________________________________ Timing Change Substate

•

•

•

•

In this state the mobile aligns itself with the System Time and the Long code timing by using the parameters LC_STATES, PILOT_PNS and the SYS_TIMES received through the Sync Message.

To understand the process we must recapitulate the structure of the Sync frames.

• The Sync frame is basically 26.666... msec long and has 32,768

chips at a speed of 1.2288 Mega Chips per sec. • A sync channel super frame is obtained by combining 3 sync

channel frame and it has 80 msec duration. • Beginning of every 25th Sync channel super frame, with a ZERO

offset Pilot PN sequence aligns with EVEN seconds. We define a Super frame as the “ Current Super Frame ” as the one during which the end of the sync message is received. The SYSTEM TIME is defined as TS which is 320 msec PAST the end of the current super frame.

• If there is a non zero Pilot PN offset, then the System Time also has the same offset, being equal to 320 msec past the end of the current super frame. The mobile receives the Long Code to be used from the Sync message and loads it into a shift register. The mobile waits till reaching the system time TS and at this point starts SHIFTING the contents of the shift register at a speed of 1.2288 Mcps.

• At this point we say that Long Code Synchronization is achieved.

After a successful Timing Change, the mobile tunes to a Paging Channel to enter the next state viz., the MOBILE STATION IDLE STATE.

The Timing Change mechanism is illustrated in the diagram opposite.


Issue II Rev 4

Timing change Sub state


Even SecondMarks

Beginning of every 25 Sync superframewith a zero Offset Pilot PN sequencecoincides with even seconds.

Sync chlsuperframe= 80 msec

Sync chl frame= 80/3=26.666..msec

Sync chl associatedwith a zero offsetPilot PN sequence

Sync chl associatedwith a Non zero offsetPilot PN sequence

Paging/traffic channelswith FRAME_OFFSETequal to zero, for anyPilot PN sequence offset

Pilot PNsequenceOffset

Traffic channel frame= 20 msec.

TS

c

end of sync message

cCurrent super frame

TS

320 msec

320 msec

Long Code shiftedout of shift registerat this point.

Illustration of Timing change mechanism.

Bangalore, India

Issue II Rev 4

Mobile Station Idle State

_________________________________________________________ MOBILE STATION IDLE STATE

In this state, the mobile monitors the Paging channel so that it- • Receives messages and orders • Initiates a registration • Receives an incoming call • Initiates a call • Initiates a message transmission

On entering this state the Mobile sets its Walsh Code to W1 , the first Primary Paging Channel. Based on the information received on the sync channel, the mobile also sets is PRATS to PRATr .

Paging Channel Monitoring Procedures

The Paging Channel is divided into a number of slots of 80 msec duration each. The mobile monitors the paging channel in a slot assigned to it. This is similar to the Paging groups that we have in GSM and basically helps conserve the mobile battery power.

Slotted Mode and Non slotted Modes

When a mobile monitors the Paging Channel only during specific slots assigned to it, we say that it is operating in THE SLOTTED Mode. Otherwise the mobile operates in the NON SLOTTED Mode. In the non slotted mode, the paging information for the mobile can come in any of the paging slots. Therefore in this mode the mobile has to monitor the Paging Channel at ALL times, over ALL the slots.


Issue II Rev 4

Mobile Station Idle State

• •

Mobile sets its Walsh Code to W1 Sets PRATs to PRATr

• Monitors Paging Channel. • Receives messages and orders • Initiates a registration • Receives an incoming call • Initiates a call • Initiates a message transmission • Paging channel divided into a number of paging slots of 80 ms duration

each. • Mobile operates in 2 modes

Slotted Mode • Monitors Paging channel only during specific assigned slots. • Slotted mode operation is during the Mobile idle state only.

Non Slotted Mode

• Mobile can get Paging messages in any of the paging slots and hence HAS to monitor all the slots all the time.


Issue II Rev 4

Paging Channel Monitoring

_________________________________________________________ Mobile Idle State - Paging Channel Monitoring

A mobile operating in the slotted mode generally monitors the paging channel for one or two slots per cycle. The mobile can specify its preferred slot cycle using the field SLOT_CYCLE_INDEX in its message towards the base station.

The minimum slot cycle length is 16 slots of 80 msec each and is equal to 1.28 seconds.

The slot cycle length , in general, is given by: T = 2I, where I is the selected slot cycle index.

The specific slot during which the mobile looks at the paging channel is given by:

SLOT_NUM = ⎣ t/4 ⎦ modulo 2048

The maximum number of paging slots in one cycle is 2048. ⎣ t/4 ⎦ is the largest integer of t/4 where t is the system time. ⎣ t/4 ⎦ modulo 2048 means the remainder of dividing ⎣ t/4 ⎦ by 2048.

The monitoring process is shown in the diagram opposite.

The figure gives an example for a slot cycle length of 1.28 seconds. The computed value of SLOT_NUM is taken as 4 in this example. The mobile starts monitoring the paging channel at the beginning of the slot for which SLOT_NUM equals 4. The NEXT slot in which the mobile will look at the paging channel again is 16 slots later; i.e., in that slot for which SLOT_NUM equals 20.

In the slotted mode, the page messages contain a field called

MORE_PAGES.

If this field is set to ‘0’ , it means that the remainder of the slot will have no more messages. With this the mobile can stop monitoring the Paging Channel as soon as possible.

If the mobile reports the loss of a paging channel, then it will enter the System Determination Substate in the Mobile Initialization State.


Issue II Rev 4

Mobile Idle State - Paging Channel Monitoring

•

•

Mobile uses SLOT_CYCLE_INDEX for deciding the slot in which it should monitor paging channel. Slotcycle length is given by T = 2I where I is the slot cycle index chosen.

• Minimum slot cycle length is 1.28 secs. ( 16 slots of 80 msec each ). • The specific slot during which the mobile looks at the paging channel is

given by: SLOT_NUM = ⎣ t/4 ⎦ modulo 2048

• The maximum number of paging slots in one cycle is 2048. • ⎣t/4 ⎦ is the largest integer of t/4 where t is the system time. • ⎣t/4 ⎦ modulo 2048 means the remainder of dividing ⎣t/4⎦ by 2048. • If mobile monitors paging channel when SLO_NUM is say, 4, then it would

look at the paging 16 slots later. • The paging message has a field “MORE_PAGES”. If this ‘0’, it means there

are no more pages and the mobile can stop monitoring as early as possible.

2047 0 1 2 3 4 . . . . ....... . . . 14 15 16 17 18 19 20 21 ... . . . ....... . . . .....

System time1.28 sec

Mobile non active A 4 non active A 20 non active

‘A’ means Reacquisition of the CDMA system.monitor paging channel


Issue II Rev 4

System Access state

_________________________________________________________

System Access State

After successful initialization and idle states, the mobile enters the System Access State which has the following Sub States:

o Upgrade Overhead Information Substate: Here, the mobile

monitors the Paging Channel until it has a current set of overhead messages.

o Origination Substate: Here, the mobile sends an “Origination Message” to the base station.

o Page Response Substate o Mobile Station Order/Message response Substate: Here, the

mobile responds to a message or order from the base station. o Registration Access Substate: Here, the mobile sends a

“Registration Message ” to the base station. o Mobile Station Message transmission Substate: Here, the mobile

sends a “Data Burst Message” to the base station.

The diagram opposite shows the various substates described above.


Issue II Rev 4

System Access State

Enter from Mobile Station Idle State

Update Overhead Information Substate

MS Order/ Msgresp. sub state

MS Idle State

MS Idle State

MS Idle State

Regn. AccessSubstate

MS MessageTransmissionSubstate

Regn. AccessSubstate

MS MessageTransmissionSubstate

Page Resp.Substate

Page Resp.Substate

MS control onTraffic Chl

MS control onTraffic Chl


Issue II Rev 4

Access Procedures

2. The mobile sends an Access Probe at a low power level to start with. The power of the mobile is increased in steps till it gets a response from the base station. The mobile transmits the SAME message in each successive access probe it transmits.

a. A response message

6. The procedures for these 2 types are different.

8. Timing between access probes of an access probe sequence is also generated pseudo randomly. After every access probe, the mobile waits for a specified period for a response from the base station. If an acknowledgment is received, the access probe sequence ends. If not the next access probe is sent after an ADDITIONAL back off delay RT= 0 to 1+PROBE_BKOFF slots.

The access procedures are illustrated in the following pages.

_________________________________________________________ Access Procedures - An overview

1. The mobile transmission on the Access channel is based on a random access procedure. The key parameters for this random access procedure are contained in the Access Parameter Message sent by the base station.

3. The access probe consists of a an ACCESS CHANNEL PRE AMBLE and an ACCESS CHANNEL MESSAGE CAPSULE.

4. The Access channel used by the mobile is chosen pseudo randomly from the Access channels available for the current paging channel. ( 32 access channels per paging channel ).

5. There are 2 types of messages that can be sent on the Access channel:

b. A request message.

7. For every access probe sequence, a back off delay specified by RS= 1+BKOFF slots is generated pseudo randomly. For request access probes, an additional random delay called the Persistence delay PD is also added.


Issue II Rev 4

Access Procedures:

• Mobile sends access probes at random.

• It sends an ACCESS PROBE at a low power level initially. • It increases power in steps till it gets a response from the base station. • Access messages could be response messages or request messages. • Start of each access probe is decided pseudo randomly. • A back off delay RS= 0 to 1+BKOFF is also generated pseudo randomly. • For REQUEST probes, an additional delay called PERSISTENCE delay

PD is also added. • Timing BETWEEN successive access probes is also generated pseudo

randomly. • After the access probe, the mobile waits for a response for a specified

time. • If no response is received it sends the next probe after an ADDITIONAL

back off delay RT = 0 to 1+PROBE_BKOFF slots.


Issue II Rev 4

Access Procedures

_________________________________________________________ Access Procedures

With reference to the diagram opposite, the following may be noted:

IP .... Initial Open Loop Power = -73-Mean i/p pwr + NOM_PWR + INIT_PWR

PD ... Persistence delay (delay continues slot by slot until the test is passed)

= 80 x ( 2 + ACC_TMO ); time out from end of slot.

RA .… Random Access Channel Number = 0 to 31 PI ..… Power Increment = 0 to 7 dB

Number of Steps = 16 max. ( 1+15)

TA ... Acknowledgment response time out delay.

= 160 to 1360 msec. ACC_TMO = 0 to 15.

RT ... Probe backoff; Random number between 0 and 1 + PROBE_BKOFF. = 0 to 15 slots.

RS ... Seq. Backoff; random between 0 and 1+ BKOFF. = 0 to 16 slots.

Persistence delay PD is applicable only for REQUEST probes.


Issue II Rev 4

Access Procedures

InitialPower

PWR_STEPPWR_STEPPWR_STEP Open Loop Power Control.

NUM_STEP - 16 max.

System Time

RS RS RS

RS RS RSPD PD PD

Access Probe Sequence

Response Message Access Attempt

Request Message Access Attempt

Seq 1 Seq 2 Seq 3 Seq 15 max

Seq 1 Seq 2 Seq 3 Seq 15 max

TA TA TART RT RT


Issue II Rev 4

Mobile station on Traffic Channel

_________________________________________________________ Mobile Station control on the Traffic Channel State

Here, the mobile exchanges Primary Traffic data packets with the base station.

In this case, the mobile disconnects a call.

In this state, the mobile communicates with the base station using the forward and Reverse Traffic Channels.

There are 5 substates as illustrated in the diagram opposite.

Traffic Channel Initialization Substate

In this state the mobile verifies it can receive the forward traffic channel and starts transmitting on the Reverse traffic Channel.

Waiting for Order Substate

In this state, the mobile waits for an “ Alert with information message ”.

Waiting for Mobile Station Answer substate

In this state, the mobile waits for the user to answer the call.

Conversation Substate

Release Substate


Issue II Rev 4

Mobile Control On Traffic Channel State

Enter from System Access State

Traffic channelInitialisation substate

Waiting for ordersubstate

Waiting for mobile stationAnswer Substate

ConversationSubstate

Release Substate

System DeterminationSubstate of Initialisation state.

Mobile terminated call; it receivesa Base stationAck order on theFwd Tfc channel

Mobileoriginated Call.It receives a Base stationAck orderon theFwd TfcChannel

Receives Maintenance order orAlert with info message.

MS useranswers.

receivesmaintenanceorder

MS releases call or gets release order Receives Alert

with informationMessage

Receivesreleaseorder


Issue II Rev 4

Registration

_________________________________________________________

Registration is a process by which the mobile tells the base station about its whereabouts. It notifies the base station of its Location, status, identification, slot cycle and other characteristics such as station class mark and protocol revision.

The PURPOSE of registration is to enable the base station to PAGE the mobile in case of an incoming call.

For operation in the slotted index mode, the mobile gives the SLOT_CYCLE_INDEX parameter so that the base station can determine the slots which the mobile could monitor.

The CDMA system supports 9 types of Registration

REGISTRATION

o Power-Up Registration o Power-Down Registration o Timer based Registration: Here the mobile performs a registration

when a timer expires. o Distance Based Registration: The mobile performs a registration

when the distance between the current base station and the one in which it had last registered exceeds a threshold.

o Zone Based Registration: The mobile registers when it enters a new zone.

o Parameter Change Registration: The mobile does a registration when it enters a new system or some of the stored parameters change.

o Ordered Registration: The mobile registers when the base station asks for it.

o Implicit registration: When a mobile station sends a successful Origination message or a Page Response message, the base station can infer the mobile’s location. This is called Implicit Registration.

o Traffic Channel Registration: Here the base station tells the mobile it is registered.


Issue II Rev 4

• Registration tells the base station about the mobile’s whereabouts.

• There are 9 different types of Registration:

4. Distance Based Registration

6. Parameter Change Registration

Registration

• It helps the base station to Page the mobile in case of an incoming call.

1. Power- Up Registration

2. Power-down Registration

3. Timer Based Registration

5. Zone Based Registration

7. Ordered Registration

8. Implicit Registration

9. Traffic Channel Registration

Only Power up and Power down registrations are presently supported.


Issue II Rev 4

Roaming

_________________________________________________________

Roaming

Definition of Systems and Networks

A base station is a member of a Cellular System and Network.

A network is a sub set of a System.

A System is given a unique identity called SID and a network within the system is identified by NID.

A network is identified by the pair ( SID, NID ). The following basic rules apply:

SID = 0 is reserved. NID = 0 is reserved. NID = 216 - 1 ( = 65535 ) is reserved to indicate that the mobile considers the entire SID ( regardless of NID ) as HOME. ( i.e., non roaming ).

The diagram opposite shows an example of systems and networks.

The mobile has a list of one or more home ( non roaming ) SID-NID pairs. If the SID-NID received on the System Parameters Message does not match any of the mobile’s non roaming SID-NID pairs, then we say that the mobile is roaming.

There are 2 types of roaming A mobile station is called a “ foreign” NID roamer, IF the SIDs are equal but the NIDs are different in the received and stored lists of SID and NID.

A mobile is called a “ foreign ” SID roamer, if the NIDs match while the SIDs are different.

For example, let the mobile have three SID-NID pairs, say (2,3), (2,0) and (3,0).If the SID-NID received from the base station is (2,3), then the mobile is not roaming because the base station’s SID-NID matches with one of the pairs in the stored list in the mobile. If the received pair is (2,7) then the mobile is roaming and is an NID roamer and if the received pair is (4,0), then the mobile is roaming and it is an SID roamer.


Issue II Rev 4

♦ ♦

• •

Definition of Systems and Networks

• A base station is a member of a Cellular System and network A network is a sub set of a System.

• A network is identified by the pair ( SID, NID ). • The following basic rules apply:

♦ SID = 0 is reserved. NID = 0 is reserved. NID = 216 - 1 ( = 65535 ) is reserved to indicate that the mobile considers the entire SID ( regardless of NID ) as HOME. ( i.e., non roaming ).

Roaming A mobile is an NID roamer if SIDr = SIDS and the NIDs do not match.

• It is an SID roamer, if the NIDs match and the SIDs don’t.

NID = p

NID = q

NID = r

SID = i

SID = l

SID = j

SID = k

FOREIGN NID ROAMER :

NIDR = NIDS.

FOREIGN SID ROAMER :

SIDR = SIDS


Issue II Rev 4

Authentication

_________________________________________________________ Authentication

Authentication is a process by which the base station confirms the identity of the mobile station.

There is a 128 bit data called the “ Shared Secret Data ( SSD ) ” which is stored in the semi permanent memory of the mobile. We say that the authentication operation is successful only when the mobile and the base station possess the same SSD.

Authentication Parameters

1. Random challenge Number (RAND): This is a 32 bit sequence sent by

the base station. This is sent on the ACCESS PARAMETERS in the Paging Channel. This is used in conjunction with SSD and other parameters for authenticating the mobile.

2. Electronic Serial Number (ESN): This is a 32bit sequence that uniquely defines the mobile set. Bits 0 to 17 are for the serial number of the mobile, bits 18 to 23 are reserved and the remaining bits are for Manufacturer’s code.

3.

4.

5.

Mobile Identification Number (MIN): This is a 34 bit sequence. This is derived from a 10 digit Telephone Directory number of the mobile. The first 24 bits ( least significant bits ) are called MIN 1. and the remaining bits are called MIN 2. Shared Secret Data (SSD): This is a 128bit data pattern stored in the mobile. This is similar to the Ki in GSM. The first subset of 64 bits called SSD-A is used for authentication purposes. The next subset of 64 bits, SSD-B is used for supporting ciphering procedures. Call History Parameter (COUNTS-P): This is a modulo 64 count held in the semi permanent memory of the mobile and is updated upon the receipt of a Parameter Update Order from the base station.


Issue II Rev 4

Authentication • Used by the base station for authenticating the mobile. • Authentication is successful only when the mobile and the base station possess

the same Shared Secret Data (SSD). • The parameters used for authentication are:

♦ Electronic Serial Number ( ESN). ♦ Mobile Identification Number (MIN). ♦ Random Challenge Memory (RAND).

Shared Secret Data (SSD). ♦ ♦ Call History Parameter (COUNTS-P)

SSD - A ( 64 bits ) SSD - B ( 64 bits )

Shared Secret Data ( S S D )

01731 24 23 18Mfr Code Reserved Serial number

Electronic Serial Number ( E S N )

M I N 2 ( 10 MSBs ) M I N 1 ( 24 LSBs )

Mobile Identification Number ( M I N )


Issue II Rev 4

Authentication during Registration – Case1

_________________________________________________________ Case 1: Authentication during Registration

The field AUTH in the System Parameters Message is set to ‘01’ for enabling the Standard Authentication Mode.

The mobile uses the RAND, ESN, MIN 1 and SSD-A data for the authentication process. It runs the Authentication Procedure to generate an 18 bit long Authentication Signature through the AUTHR field in the Registration Message.

The mobile sends the AUTHR and a parameter called RANDC,(8 MSBs of RAND) to the base station.

The base station compares the RANDC received from the mobile with its internally stored value of RAND. In fact it is derived from the RANDC coming from the mobile.

The base station also retrieves the ESN and MIN of the mobile from its data base based on the COUNT value received from the mobile.

It runs the Authentication Procedure locally, by using the internally stored SSD-A and generates its own AUTHR. If the AUTHRmobile matches the AUTHRbase, then the authentication is successful.

If the comparisons fail, then the base stain may either do a “ Unique Challenge-Response ” procedure OR initiate an “ SSD Update ” sequence.

The process is illustrated in the diagram opposite.


Issue II Rev 4

Case 1: Authentication During Registration:

RAND ESN MIN 1 SSD-A

AuthenticationAlgorithm

AUTHRm (18 bits)

RAND ESN MIN 1 SSD-A


AUTHRb (18 bits)

Derived fromRANDC

Derived fromCOUNT

Derived fromlocal memory

Mobile end.

AUTHRm = AUTHRb ?Yes No

Authentication Successful Perform Unique Challenge-ResponseorSSD Update Procedure

RANDC


Issue II Rev 4

Unique Challenge – Response Procedure

_________________________________________________________ Case 2: Unique Challenge-Response Procedure

This is initiated by the base stain in the event of an unsuccessful authentication attempt. This can be done either on the Paging and Access Channels or on the Forward & Reverse Traffic Channels.

The base station sends to the mobile an Authentication Challenge Message. It generates a 24 bit data called RANDU and sends it on the Challenge Message.

The mobile sets the authentication parameters using 24 MSBs of RANDU and 8 MSBs of MIN 2 in its RAND field.

The mobile performs an authentication procedure and returns the AUTHR to the base station.

The base station also does a similar calculation, using the internal parameters including the SSD-A.

If the comparison fails, then the base station may either deny further access to the mobile or drop the call in progress or initiate an SSD Update Procedure.

The above mentioned process is illustrated in the diagram opposite.


Issue II Rev 4

Case 2: Unique Challenge-Response Procedure:

RAND

ESN MIN 1 SSD-A


AUTHRm (18 bits)


AUTHRb (18 bits)

Derived fromRANDC

Derived fromCOUNT

Derived fromlocal memory

AUTHRm = AUTHRb ?Yes No

Authentication Successful

Mobile receives Authentication Challenge

RANDU24 bits

MIN 28 bits

AUTHR and RANDC

ESN MIN 1 SSD-ARANDU24 bits

MIN 28 bits

Deny Access orDrop Call in Progress orInitiate SSD Update Procedure.


Issue II Rev 4

SSD Update Procedure

Case 3: SSD Update Procedure

The base station sends an SSD Update Message either on the Paging Channel or the Forward Traffic Channel. It generates an RANDSSD number and sends it on the update message.

The mobile then does an SSD_Generation procedures and obtains new values for SSD-A and SSD-B.

_________________________________________________________

This is done when an authentication procedure fails. This is initiated by the base station. An SSD_Generation Procedure is used in conjunction with mobile specific data and the Mobile’s A-Key.

The A-Key of the mobile is 64 bits long and is unique to the mobile. It is known only to the mobile and the HLR. It is similar to the Ki in GSM.

The update procedure is indicated in the diagram in the opposite page.

After this the mobile generates a 32 bit random number called “ RANDBS” and sends it on a Base Station Challenge Order in the Access Channel or the Reverse Traffic Channel.

Both the mobile and base stations perform the Authentication procedures to get AUTHBS values and these are compared. For this comparison, the base stations ends its AUTHBS through a Base Station Challenge Confirmation Order.

If the comparisons match then the mobile performs an SSD update procedure at the end of which it sends an SSD Update Confirmation Order to the base station. It also sets the SSD-A and SSD-B values to the new values. The base stain also sets its corresponding parameters to the new values.

If the comparison fails, then the mobile discards the new values of SSD-A and SSD-B and send an SSD Update Rejection Order to the base station.

Again, if the mobile does not receive the Base Station Challenge Confirmation Order within a time limit set by the timer T64m,(= 10 sec) the new values are discarded and the up date procedure is terminated.


Issue II Rev 4

Case 3: SSD Update Procedure

Mobile Station Base StationSSD Update Message

RANDSSD

RANDSSD (56) ESN A-Key (64 bits)

SSD_GenerationProcedure

SSD-A New SSD-B New

RANDBS

Authentication Procedure

AUTHBSm = AUTHBSb ?

RANDSSD (56) ESN A-Key (64 bits)

SSD_GenerationProcedure

SSD-A New SSD-B New

Authentication Procedure

Base Stn Challenge Order RANDBS

Base Stn Challenge Confirm

Yes... SSD Update Confirmation OrderNo ... SSD Update Rejection Order


Issue II Rev 4

Handoff Procedures

_________________________________________________________

Hand-off Procedures

There are basically 3 major types of Hand-offs in CDMA.

o Less Power is needed on the Reverse Traffic Channel

o CDMA - CDMA Hand-off: Here, the mobile is transitioned between disjoint cells having different frequency assignments.

Soft hand-offs

These are Hand-offs in which the mobile initiates communications with a neighbouring base station WITHOUT breaking communications with the old base station. We also define a softer hand-off as one that takes place between sectors of the same cell site. Soft hand-offs are done only between cells having the same CDMA channel ( frequency ) assignments. A soft hand-off is a MAKE BEFORE BREAK type of connection.

A key benefit of soft hand-off is the diversity it provides at the boundaries of cells. ( this is because, at the boundaries, the mobile is talking to both the new and old base stations at the same frequency.) Diversity on the Reverse Channel means that :-

o This means that the Interference in the Reverse channel is minimum

o Hence this results in an Optimum Reverse Link capacity. Hard Hand-offs

There are 2 types:

o CDMA-Analog Hand-offs: Here, the mobile moves from a CDMA traffic channel to an analog channel. Hard hand-offs are like BREAK BEFORE MAKE connections.

The concepts of soft and hard hand-offs are illustrated in the diagram

opposite.


Issue II Rev 4

Hand-off Procedures:

♦ CDMA - CDMA cells

♦ Break before Make connections.

• Soft Hand-offs: ♦ Between Cells of the same frequency. ♦ Connection maintained at all times. Mobile talks to both old and new base

stations. ♦ Provides diversity for the traffic channels near cell boundaries; this results in

optimum reverse channel capacity. ♦ Make before Break connections.

• Hard Hand-offs: ♦ Between disjoint cells.

♦ CDMA - Analog cells.

Cell B Cell A Cell B Cell A Cell B Cell A

Mobile on Cell B Soft Handoff to Cell B Mobile on Cell A

Hard Handoff example:Cell B Cell A Cell B Cell A

Mobile on Cell B Mobile on Cell A


Issue II Rev 4

Pilot Sets

_________________________________________________________ Pilot Sets

The hand-off mechanism is basically triggered by the level of the pilot signals coming from the neighbouring cells. (A pilot is identified by a PILOT channel with a Pilot sequence offset and a specific frequency assignment. A pilot is associated with the forward Traffic Channels of the same CDMA channel. All pilots in a pilot set , therefore , have the same frequency assignment. )

The pilots associated with the Forward Traffic Channels assigned to the mobile station.

This contains a list of neighbouring pilots whose signal strengths are strong enough to make them candidate pilots. This list is entered through the data base. Even if a pilot from an adjoining cell is very strong, the mobile will not look at if it is NOT menioned in the neighbour list.

The mobile looks for pilots on the current CDMA frequency assignment to detect the presence of CDMA channels. When it detects a pilot that is different from its present pilot set and whose power level is above a certain threshold, the mobile sends a Pilot Measurement Message to the base station. The latter ten assigns a traffic channel associated with that Pilot channel and asks the mobile to do a soft hand-off.

Thus the entire operation of hand-offs is dependent on searching for the pilot. The Pilot search parameters and the rules for measurement of pilot strength are governed by the following SETs of pilots:

Active Set

Candidate Set

Those pilots which are NOT in the current Active Set but have sufficient signal strength to qualify for hand-off.

Neighbour Set

Remaining Set

The set of all pilots other than the three types mentioned above.


Issue II Rev 4

Pilot Sets

• Hand-offs are done by measuring pilot signal strengths from neighbouring cells.

• Measurement Message sent to base station when a pilot of adequate strength, not belonging to the mobile’s current assignment of traffic channels is detected.

• Hand-off process is dependent on pilot searches.

• Pilots can be grouped in 4 Sets: ♦ ACTIVE SET ♦ CANDIDATE SET ♦ NEIGHBOURING SET ♦ REMAINING SET

ACTIVE SET

CANDIDATE SET

NEIGHBOUR SET REMAINING SET


Issue II Rev 4

Pilot search-Search Windows

_________________________________________________________

The Mobile Unit searches for the pilot over a SEARCH WINDOW. The mobile unit centres the search window for each Pilot in the Active Set and the Candidate Set, around the earliest arriving multipath component of the pilot.

For the Neighbour and Candidate Sets, the mobile centres the search window around the pilot’s PN offset using the mobile’s time reference.

Pilot Search - Search Windows

We said that the mobile identifies a pilot with reference to its PN offset. However, while looking for a pilot, the mobile is NOT limited to the exact offset of the short PN code.

Remember the mobile environment is full of multi paths caused by reflections. This means that the multi path components of the pilot will arrive a few chips LATER than the direct path.

Window sizes are specified in Number of short PN chips as shown in the Table given below.

The SRCH_WIN values are the stored values in the mobile. The values given in the table specify the total search range.

For example, if the value for SRCH_WIN_AS = 10, it means a 100 chips search window or ± 50 PN chips around the search window centre.

SRCH_WIN_ASSRCH_WIN_NSSRCH_WIN_RS

Window Size in PN Chips.

SRCH_WIN_ASSRCH_WIN_NSSRCH_WIN_RS

Window Size in PN Chips.

0 8 4 60 1 6 9 80 2 100 8 10 3 10 11 130 4 14 160 12 5 20 13 226 6 28 14 320 7 40 15 452


Issue II Rev 4

Pilot Search - Search Windows

• Pilot Search is around a Search window • Multipath components arrive later than the direct path component of the

pilot. • For Active and Candidate sets, window is centered around the earliest

arriving multipath component of the pilot. • For the other sets, it is around the short Code PN offset as per the

mobile’s timing reference. • window sizes are specified in units of PN chips.

Search windows

Multipath components in a search window


Issue II Rev 4

Parameters Used in Hand-offs

_________________________________________________________ Parameters Used in Hand-offs

The following parameters are very important in hand-off situations:

o T_ADDS: This is the PILOT DETECTION THRESHOLD. o T_COMPS:This is the ACTIVE SET Vs CANDIDATE SET

COMPARISON THRESHOLD. o o

T_DROPS: This is the PILOT DROP THRESHOLD. T_TDROPS: This is the PILOT DROP TIMER VALUE.


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o o

o o

Parameters Used in Hand-offs

T_ADDS: This is the PILOT DETECTION THRESHOLD. T_COMPS:This is the ACTIVE SET Vs CANDIDATE SET COMPARISON THRESHOLD. T_DROPS: This is the PILOT DROP THRESHOLD. T_TDROPS: This is the PILOT DROP TIMER VALUE.


Issue II Rev 4

Pilot Strength Measurements

The mobile station helps the base station in the hand-off process by measuring the pilot strength from the neighbors and reporting the measured value back to the base station. The mobile uses the searcher element in the Rake receiver for this purpose. The mobile calculates the EC / N0 of the received pilot signal for determining the signal strength. In general, the mobile transmits a Pilot Strength Measurement Message to the base station (the current, active base station) under the following conditions:

o One of the pilots in the Active Set has DROPPED below the

threshold T_DROPS and the timer T_TDROP has expired.

o

o

T_TDROP

Pilot Strength - Measurements _________________________________________________________

The mobile maintains a hand-off timer (T_TDROP) for each pilot in the Active and candidate sets. It starts the timer whenever the pilot strength falls below T_DROP. It resets and DISABLES the timer as and when the signal strength rises above the threshold. When T_TDROP is ZERO, the mobile considers that the timer has expired within 100 ms of enabling it. Otherwise, it considers the timer expired WITHIN 10 % of the timer expiration value shown in the Table given below for T_TDROPS.The strength of a Pilot in the Candidate Set exceeds the level of a pilot in the Active Set by a value T_COMPS x 0.5 The strength of a pilot in the Neighbor Set or the Remaining Set exceeds the Pilot Detection Threshold T_ADDS.

T_TDROP Timer Expiration Timer Expiration

0 = o.1 sec 8 27 1 1 9 39 2 2 10 55 3 4 11 79 4 6 112 12 5 9 13 159 6 13 14 225 7 19 15 319


Issue II Rev 4

•

♦

♦

♦ Neighbor Set or Remaining Set pilot strengths exceed threshold

T_ADDS.

Pilot Strength Measurements • Hand-off process is based on pilot strength of neighboring cells.

Mobile determines pilot strength from EC / N0 of the pilots from the near by cells.

• Pilot Strength Measurement Message to base station is sent when:-

Active Set Pilot falls below T_DROPS and the timer T_TDROPS has expired.

Candidate set Pilot strength exceeds that of Active set by T_COMPS x 0.5


Issue II Rev 4

Hand-off Procedures – flow chart

Hand-off Procedures

The Hand-off procedure is depicted in the diagram opposite.

If the pilot from the neighboring cell exceeds the pilot level in the Active set of the current set by T_COMP x 0.5, then the mobile sends a measurement report to the base station.

The latter sends the mobile a Hand-off Direction Message, which consists of:

o CDMA Channel Assignments

The mobile sends a Hand-off Completion Message to both the base stations. At this point we say that the mobile is in Soft Hand-off.

_________________________________________________________

o The Hand-off Message Direction Message Sequence Number

o Search Window Size o Active Set list which includes both the old and new pilots o T_ADD ( PILOT DETECTION THRESHOLD ) o T_DROP ( PILOT DROP THRESHOLD ) o T_TDROP ( PILOT DROP TIMER ) o T_COMP ( ACTIVE Vs CANDIDATE COMPARISON THRESHOLD )

The mobile acquires the new base station while maintaining the link with the old base station.


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Hand-off Procedure - a Flow Chart

Search for pilot

Neighbor Set Remaining Set

PX exceeds T_ADD ?No

Yes

1. Move the pilot to Candidate Set

2. Send Measurement Report to base station.

No PXexceeds an active pilot by

T_COMP x 0.5 ?

Keep Pilot in Candidate Set • Send Measurement Report• Receive H/O Direction Message • Move pilot to Active Set• Send Handoff Completion Message

Yes


Issue II Rev 4

3. Mobile TRANSFERS the pilot to the Active Set and sends a Hand-off Completion Message to the base station.

Figure (b) illustrates the messaging triggered by a pilot in the candidate Set as its strength gradually rises above the active set pilots.

Hand-off threshold comparisons _________________________________________________________

Hand-off Threshold Comparisons

Fig.(a) in the opposite shows an example of messages exchanged between the mobile and the base station during a typical hand-off process.

1. Pilot Strength exceeds T_ADD. Mobile sends a measurement report

to the base and TRANSFERS the pilot to Candidate Set. 2. Base station sends a Hand-off Direction Message.

4. Pilot Strength falls below T_DROP. Mobile starts hand-off drop timer. 5. Hand-off drop timer expires. Mobile sends a measurement report. 6. Base station sends a Hand-off Direction Message. 7. Mobile moves the pilot from the Active Set to the Neighbour Set and

sends a Hand-off Completion Message.


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Hand-off Threshold Comparisons Figure ( a ): Hand-off Threshold Example:

T_ADDT_DROP

PilotStrength

Time1 2 3 4 5 6 7

Neighbour SetCand.Set

Active Set Neighbour Set

Figure ( b ) Pilot Measurement triggered by a Candidate SetPilotStrength

Time

T_ADD

Pilot P0

T_COMP x 0.5 dB

T_COMP x 0.5 dB

t0 t1 t2

Pilot 1

Pilot 2

t0 - P0 greater than T_ADDt1 - P0 greater than P1 + T_COMP x 0.5t2 - P0 greater than P2 + T_COMP x 0.5


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Case1:Mobile Originated Call

_________________________________________________________ Case 1: Mobile Originated call


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Case 1: Mobile Originated call

Mobile Station Base Station

• Sends ‘ Origination Message ’ Access channel

•Receives Origination Message.•Sets up a Traffic Channel•Starts sending Null Tfc data.•Sends ‘Channel Assignment Messagge’

Paging Channel•Receives Paging channel•Sets up Reverse Traffic Channel•Receives N5m consecutive valid frames.•Starts sending Traffic Channel Preamble •Acquires Reverse Tfc Channel.

•Sends ‘Base Station Ack Order’.

Reverse Tfc Channel

Forward Tfc Channel•Receives Ack from base station

•Starts sending Null Traffic data.•Starts processing Primary Traffic in accordance with Service option 1.

Reverse Tfc Channel

•Receives data from mobile.•Sends ‘Service Option Response Order. ’

Forward Tfc Channel

Sends ‘ Origination continuation Message ’•Receives Ring back tone.

Reverse Tfc Channel

•Sends ‘ Alert with Info. Message ’Forward Tfc Channel

•Called Sub Answers. Alert •message sent again ( tone off )

Forward Tfc Channel•Ring stops•Conversation Starts

•Conversation


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Case2: Mobile Terminated call

_________________________________________________________ Case 2: Mobile Terminated call


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Case 2: Mobile Terminated Call:

Base Station Mobile Station

•Sends “ Page Message or Slotted Page Message ”

Paging channel

Access Channel•Sends Paging Response Message•Receives Page response.

•Sets up traffic channel•Begins sending Null traffic data•Sends Channel Assignment Paging channel

•Receives N5m consecutive frames•Sets up reverse Trafic channel•Sends Traffic Channel Preamble

Reverse Traffic channel

•Acquires Reverse Traffic Channel•Sends Base Station Ack Order•Sends Service Option Response Order.

Forward Traffic channel

•Processes Primary Tfc data in accordance with service option 1.

•Sends Alert with Info Message Forward Traffic channel•Starts ringing•User answers•Stops Ringing•Sends Connect Order

Reverse Traffic channel

•Conversation •Conversation


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Call Disconnect

_________________________________________________________ Case 3: Mobile Initiated Call Disconnect Case 4: Base Station Initiated Call Disconnect


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Case 3: Mobile Initiated Call Disconnect

Mobile Station Base station

•Detects user initiated Disconnect•Sends ‘ Release Order ’

Reverse Traffic Channel

•Sends ‘ Release Order ’Forward Traffic Channel

•Enters “ System Determination Substate ” of the Mobile State Initialisation State.

Case 4: Base Station Initiated Call Disconnect

Base Station Mobile station

•Detects Call Disconnect•Sends ‘ Release Order ’

Forward Traffic Channel

•Sends ‘ Release Order ’ReverseTraffic Channel

•Enters “ System Determination Substate ” of the Mobile State Initialisation State.


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Call Processing during Soft Hand Off

_________________________________________________________ Case 5: Call Processing During Soft Hand-off:


Issue II Rev 4

Case 5: Call Processing During Soft Hand-off


< User Conversation using A> < User Conversation using A>•Pilot B level exceeds T_ADD.•Sends “ Pilot Strength Measure - ment Report ”.


•‘A’ receives Measurement Report.•‘B’ starts sending Tfc data on the Forward Traffic Channel and acquires the Reverse Traffic chl.•‘A’ and ‘B’ send Handoff Direction Message to use A and B

Forward Traffic Channel•Receives Handoff Direction.•Acquires ‘B’: Starts using Active Set A,B.

•Sends Handoff completion message Reverse Traffic Channel•‘A’ and ‘B’ receive Completion Message.

•Handoff Drop Timer for Pilot A expires.•Mobile sends measurement report

Reverse Traffic Channel •A and B receive Measurement report.•A and B send Handoff Direction Message to use pilot B only.

Forward Traffic Channel•Receives Handoff Direction•Sends Handoff Completion Message Reverse Traffic Channel •A and B receive completion

•message.•‘A’ stops transmitting on the •Forward channel and receiveing •on the reverse traffic Channel.

< User Conversation using B> < User Conversation using B>


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Case 6: Call processing during sequential soft hand off

_________________________________________________________ Case 6: Call Processing During Sequential Soft Hand-off :


Issue II Rev 4

Case 6: Call Processing During Sequential Soft Hand-off : This is an example of Hand-off when the mobile is talking to two base stations during a Hand-off process and another hand-off to a third base station C becomes imminent. Part -1:


< User Conversation using A and B> < User Conversation using A and B>•Pilot C level exceeds T_ADD.•Handoff Drop Timer for Pilot A expires.Sends “ Pilot Strength Measure - ment Report ”.

Reverse Traffic Channel •‘A’ and ‘B’receive Measurement Report. decide that the new Active set should have ‘B’ and ‘C’.•‘C’ starts sending Tfc data on the Forward Traffic Channel and acquires the Reverse Traffic chl.

•‘A’ ‘B’and ‘C’ send Handoff Direction Message to use B and C

Forward Traffic Channel•Receives Handoff Direction.•Acquires ‘C’: Starts using Active Set B,C.•Sends Handoff Completion Message•HandoffDrop Timer of B expires

Reverse Traffic Channel •‘A’ ‘B’and ‘C’ receive Completion Message.

•Mobile sends measurement reportReverse Traffic Channel

•‘A’ stops transmitting on the Forward channel and receiveing on the reverse traffic Channel.

•B and C receive Measurement report

continued ....


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Case6: Call processing during sequential soft hand off _________________________________________________________ Case 6: Call Processing During Sequential Soft Hand-off : Part 2


Issue II Rev 4

Case 6: Call Processing During Sequential Soft Hand-off : Part -2:



Forward Traffic Channel

continued ....

( continued ) ( continued )

•B and C send Handoff Direction Message•Receives Handoff Direction

Message

•Starts using Active Set c

•Sends Handoff Completion Message •B and C receive Handoff

Completion Message

•B stops using the Forward and Reverse Traffic channels.

•User conversation using C •User conversation using C


Issue II Rev 4

SECTION 8

Introduction to cdma2000


Issue II Rev 4

Section 8 Introduction to cdma2000 235 Objectives 237 Introduction 238 Overview of 2G network Architecture 240 3G Network Architecture 244 IP Mobility 252 RAN Mobility 254 CN Mobility 256 3G Wireless Systems 258 cdma2000 standards 266 cdma2000 Network architecture 270 cdma2000based 3G network 274 cdma2000 RAN interfaces 276 Circuit Switched Data Call 280 Packet data call 282 cdma2000 protocol layer 284 cdma2000 physical layer 286 Turbo Encoder 290 cdma2000 forward link 302 Pilot Channels 304 Sync Channels 306 Forward Link Radio Configurations 318 Reverse link radio configurations 320 Reverse link channels 322 Orthogonal Walsh codes 324 RC Support by Mobile 330 Packet Switched call setup 354 Future of CDMA 356 1X Evolution Alternatives 360 Migration from 2G to 3G 372 Migration paths to 3G 374 1X Network Overview 378 Radio Access network 382 Access node 388 Packet Data network 394 Network Operations and Maintenance Description 402 Motorola cdma2000 network migration 408

Appendix A 410 Appendix B 413

Appendix C 417


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Objectives _________________________________________________________

Objectives


Explain cdma2000 packet data architecture Learn interfaces/protocols between network nodes Key components like PDSN, CBSC, 1XBTS cdma2000 radio interfaces Motorola migration paths


Issue II Rev 4

Introduction

_________________________________________________________ Introduction

The 1G systems introduced the cellular concept in which multiple antenna sites are used to serve an area. The coverage area of a single antenna is called a cell.1G systems uses analog transmission technologies .So it is best suited for Voice services, as data communications can be cumbersome. The 2G technologies begin in the late 1980s and early 1990s.The primary motivation was increased system capacity. This was achieved by using more efficient digital-radio technologies that enabled the transmission of digitized compressed speech signals. This technology supports data services as high as 14.4 Kb/s .2G technologies typically uses circuit switched techniques which is not very efficient for sending packet data such as that sent on internet. This inefficiency makes the use of wireless data more expensive for the end user than it needs to be. The evolution from 2G to 3G is occurring in early 2000s.The 3G systems support high speed data services as high as 2Mb/s Data can be transferred using packet switching techniques rather than circuit switching techniques. So it is more efficient, less expensive and opens up the possibility of cost-effective internet access, access to corporate intranets and a host of multimedia services.


Issue II Rev 4

Evolution of Wireless Technologies


Issue II Rev 4

Overview of 2G network Architecture

_________________________________________________________ 2G Network Architecture in IS-95 – An Overview

The network architecture is based on IS – 41 network protocol. The IS-95 air interface protocol is used between the MS and base station. The interface between BSC and BTS is vendor specific. The interface between BSC and MSC is defined by Inter Operability Specification (IOS) protocol. This is an optional interface and most vendors have their own proprietary protocols. IOS also defines support for mobility and soft handoff in an IS-95 based air interface. IS-41 protocol is used for communication between most network elements. IS-41 also defines the interface between two MSCs to ensure interoperability between wireless networks from different vendors. IS-41 supports only call signalling and does not cover network management. Voice calls are routed through the MSC. For circuit and limited packet data services, the MSC or BSC connects to an Inter Working Function (IWF)


Issue II Rev 4

2G Network Architecture in IS-95 – An Overview


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2G Limitations

_________________________________________________________

2G Limitations

Bandwidth Limitations

The 2G systems support data rates less than 64kbps.In fact, most systems support data rates up to 14.4kbps.Most technologies use radio channels that are designed to support only voice services. The CDMA systems use a 1.25 MHz bandwidth channel and the options provided allow a maximum data rate of 115.2kbps.

Limited Roaming capabilities

Multiple air interface technologies are used in 2G networks and they are not compatible with each other. Multi-mode mobile stations are rare, and those available support only two modes. In addition, on the network side, the underlying incompatibility between IS-41 and GSM MAP prevents roaming across systems using different network protocols.

Data services

2G services are primarily designed for Voice services. Most systems support only data rates up to 14.4 kbps. Service such as Internet access, requiring support of data rates greater than 100kbps are not possible using existing 2G technologies. The data services supported are primarily circuit oriented.

Packet data Networks

Packet data is typically intermittent and busy in nature .If the circuit switched approach is used to support packet data services, this would result in inefficient usage of radio and network resources. Most 2G technologies have no protocol support for packet data services.


Issue II Rev 4

2G Limitations

• Capacity • Limited Roaming capabilities

• Limited support for packet data

• No multimedia

• Data rate 14.4-64kbps

• Uni-service network


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3G Network Architecture

_________________________________________________________

3G Network Architecture Mobile Station (MS)

This is the user terminal .The user terminal provides wireless Network Access and user applications with appropriate user interface such as voice application and keys to dial a telephone number, fax, web browser and other interfaces to connect a laptop computer to allow network access to a user’s laptop.

Radio Access Network (RAN)

• Provides Radio channels to the mobile station • Radio level mobility: Allow the users to move within RAN during

handoff • Authentication and security over radio channels • Quality of service (QOS) over the radio channels • Power control, radio resource management, network information

broadcasting

Core Network (CN)

The core network is the network of components that provide access to users over the network as well as network services such as voice mail, web server, billing There are two types of core networks

Circuit switched core network (CS-CN)

Provides services using circuit switched transport and interconnects with circuit switched networks such as PSTN

Packet switched Network (PS-CN)

Uses packet switched technologies and interconnects with Internet.


Issue II Rev 4

3G Network Architecture


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Data Rates

_________________________________________________________

Data Rates – Asymmetric in Nature

The underlying protocol for the www is the Hyper Text Transfer Protocol (HTTP). When a mobile user wants to retrieve a web page, he sends an HTTP request. The HTTP request may be of few kilobytes. The HTTP response carries the web page from server to the user. If the page contains images and multimedia information, it may span a few megabytes. Thus, there is asymmetry in the data rate transferred in both directions. If equal bandwidth channels are allocated in both directions over the air, it leads to enormous waste and a low spectral efficiency in the reverse link. The 3G radio interfaces allow for flexible, unequal allocation of bandwidth in different directions. This leads to higher spectral efficiency, a requirement of International Mobile Telecommunication (IMT-2000).


Issue II Rev 4

Data Rates – Asymmetric in nature

• Bandwidths requirements in reverse and forward channels are different which leads to efficient radio spectrum utilization.

• Useful for applications like web access and cable TV


Issue II Rev 4

Bandwidth on Demand

_________________________________________________________

Bandwidth on Demand

Bandwidth on demand (BOD) is required to support intermittent and bursty behavior of web applications. Depending on the amount of data to be transmitted, either the user terminal may request bandwidth or network may allocate bandwidth as required. During periods of no data transmission dedicated radio traffic channels are not allocated to the user. When there is data to be transmitted by either user or network, dedicated radio channels may be assigned to the user.

The 3G technologies generally support BOD by having common control channels, low rate dedicated channels and variable rate traffic channels. This is the strategy followed

•When there is sufficient information to be exchanged, a dedicated traffic channel is allocated to the user. •Allocate a low rate dedicated control channel when sufficient data transmission is likely within a short time period •Deallocate all dedicated channels from the user if there has been no data exchanged with the user recently.


Issue II Rev 4

Bandwidth on Demand


Issue II Rev 4

Concurrent Channels

_________________________________________________________

Concurrent Channels

The 3G radio technologies are designed to support varying information rates. The bandwidth can be allocated on demand and dynamically results in high-spectral utilization. One of the goals of 3G networks is to provide multimedia services. In multimedia services, there are several media streams such as audio, video and text data. Each stream may be carried in separate concurrent channels that have their own data rates .The 3G radio interfaces can allocate multiple, concurrent radio channels for multimedia services .The protocol structure has been enhanced to control multiple channels together and provide different levels of Quality of Service (QOS) on different channels.


Issue II Rev 4

Concurrent Channels


Issue II Rev 4

IP Mobility

_________________________________________________________

IP Mobility

IP mobility is the ability to move with an IP address after an application is connected using that IP address. It allows user to be mobile while connected to the desired IP based services. The 2G networks only supported mobility for Circuit Switched connections, with the exception of Cellular Digital Packet Data or CPDP. In the 3G different levels of IP mobility are supported. For example, the RAN (Radio Access Network) mobility is supported by handoffs between the cell sites.


Issue II Rev 4

IP Mobility

•Ability to move with an IP address while the connection using the IP address is active. •IP mobility may be provided by a combination of RAN mobility and CN mobility. •RAN Mobility- Handoff, Cell selection/reselection. •CN IP Mobility-Mobile IP.


Issue II Rev 4

RAN Mobility

_________________________________________________________

Mobility in 3G Networks: RAN Mobility

RAN allows user to move around while connected. BSC or Radio Network Controller (RNC) may allow user to mover within the cells it controls with out any participation form Packet Data Node (PDN) in the core network. The RAN provides mobility using handoff, cell selection or cell-reselection process


Issue II Rev 4

Mobility in 3G: RAN Mobility


Issue II Rev 4

CN Mobility

_________________________________________________________

Mobility in 3G Networks: CN Mobility

RAN allows user to move around while connected. BSC or Radio Network Controller (RNC) may allow user to mover within the cells it controls with out any participation form Packet Data Node (PDN) in the core network. The RAN provides mobility using handoff, cell selection or cell-reselection process


Issue II Rev 4

Mobility in 3G Networks: CN Mobility


Issue II Rev 4

3G Wireless Systems

_________________________________________________________

3G Wireless Systems

The International telecommunication Union (ITU) facilitates 3G standards development .In the early 1990’s ITU formed a subgroup called International Mobile communications-2000 (IMT-2000) The term Third Generation Mobile systems or 3G is used to define an umbrella of standards and systems for the next generation of terrestrial and satellite based mobile systems.


Issue II Rev 4

3G Wireless System

•Third Generation of Wireless systems •Developed under International Telecommunication Union(ITU) and other regional bodies •Designed to provide:

- High data rate services - Advanced multimedia services - Global roaming

- Other features


Issue II Rev 4

3G Wireless Technologies

_________________________________________________________

3G Wireless Technologies There are multiple 3G wireless technologies being defined and deployed around the world today. These technologies are successors to existing 3G technologies cdma2000 is the successor to IS-95 systems, cdma2000 defines two different options for 3G technologies. The option differs in the amount of spectrum used. The Spreading Rate (SR1) operates in the 1.25 MHz band and is known as 1x system. The Spreading Rate (SR3) operates in the 3.75 MHz band and is known as 3x system. Two other proposals are also being considered in cdma2000 referred to as 1XEVDO and 1XEVDV. 1XEVDO is a data only solution that enables a bandwidth of 2Mbps without any mechanism for voice. 1XEDV is another standard for a technology that will allow both voice and data applications


Issue II Rev 4

3G Wireless Technologies


Issue II Rev 4

What is cdma2000

_________________________________________________________

What is cdma2000


Issue II Rev 4

What is cdma2000


Issue II Rev 4

Key features

_________________________________________________________

cdma2000 Key Features

It is designed to meet requirements for the next generation evolution of the current IS-95 family of standards and includes various features and enhancements

•Support for overlay configurations within the same physical channel as existing IS-95 systems •Supports wide range of data rates – Indoor Office (2Mbps), Indoor to Outdoor/Pedestrian (384 kbps), and Vehicular (144 kbps) •Various techniques to improve the system capacity for voice calls e.g. transmit diversity, fast forward power control, reverse pilot channel, new coding schemes etc •Improvements in System Access that reduces collision and supports sending short data bursts on a common channel •Quick Paging Channel is introduced to enhance paging strategy to improve standby battery life of mobile station •An advanced multimedia Quality of Service (QoS) control capability supporting multiple concurrent voice, high-speed packet data and high speed circuit data services along with sophisticated QoS management capabilities •Support for Removable User Identity Module (R-UIM) for global roaming


Issue II Rev 4

Key Features of cdma2000

•Supports Packet Data and Higher data rates (614.4 Kbps & 2 Mbps) •Increased System Capacity (>50%) •Improved System Access •Improved Paging Mechanism •Other Features

–Multimedia Services –Quality of Service (QoS) –Support for R-UIM


Issue II Rev 4

cdma2000 standards

_________________________________________________________

cdma2000 Standards evolution

The first version of the IS-95 standard was released in 1994, followed by IS-95A in the beginning of 1995, and J-STD-008 and IS-95B in 1997. The deployment of the wireless system that complies with one of these standards is also known as cdmaOne In 1998, TR45.5 subcommittee of TR45 of TIA (Telecommunication Industry Association – North American Telecommunications Standards Organization) proposed an air interface solution that would meet IMT-2000 requirements and also backward compatible with IS-95. 1x solution would achieve some of the data rates required by IMT-2000, but 3x solution was required to meet highest data rate of 2Mbps The initial version of IS-2000 was released in 1999 and IS-2000A was published in April 2000. Currently, IS-2000B is in development. Also in 2000, a separate standard IS-856 was published to support high-speed packet data services up to 2 Mbps. This standard was pioneered by Qualcomm and is also known as High Data Rate (HDR) or 1x Evolution for Data only (1xEV-DO). At present, the development of 1x Evolution for Data and Voice (1xEV-DV) standard is underway in the global standards body


Issue II Rev 4

Cdma2000 Standards Evolution


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Nomenclature

_________________________________________________________

Nomenclature

The IS-95A was specified in North America for 800Mhz frequency band. A version to support 1900 MHz PCS band was later published as J-STD-008. Both of these collection of standards collectively called as IS-95. Later, the CDMA Development Group (CDG) gave a trade name to these wireless systems as cdmaOne IS-2000 family of standards started in 1988 and two versions of this standard have been published, namely, IS-2000 and IS-2000A. CDG adopted trade name for this family of standards as cdma2000


Issue II Rev 4

Nomenclature

IS-2000, IS-2000A cdma2000 cdma2000

IS-95A, ANSI J-STD-008, IS-95B

IS-95cdmaOne

Family of Standards Commonly Used Name

Trade Name


Issue II Rev 4

cdma2000 Network Architecture _________________________________________________________

cdma2000 Network Architecture

IMT-2000 group is formed in mid 1990’s to specify requirements for 3G wireless system. These systems contains three high level components: The Radio Access Network (RAN), The Circuit Switched Core Network (CS-CN), and the Packet-Switched Core Network (PS-CN). The BSC and the BTS provide the RAN function, MSC/VLR and HLR/AC provide the CS-CN function, PDSN (Packet Data Serving Node) provides primary element of PS-CN. PS-CN provides connectivity to Internet, and leverages standard Internet protocols. It provides interface to RAN through the Radio-Packet (R-P) interface. It routes packets from the Internet to the RAN and vice versa. The PS-CN uses the Mobile IP protocol to provide mobility for packet data services. Mobile IP entities such as Home Agent (HA) and the Foreign Agent (FA) are also included in the PS-CN. The AAA server provides Authentication, Authorization and Accounting functions of the PS-CN

Standards for cdma2000 Networks

IS – 41 defines the interface between different core network components including MSC, HLR, VLR and AC. IS-41 is used only in CS-CN. In addition cdma2000 leverage Internet standards like RADIUS, Mobile IP and IPSec for packet data operation

The IS-2000 defines the over-the-air interface standard and is the successor for the IS-95 standard

The Network standards for cdma2000 include Inter Operability Specification (IOS) and IS-41. IOS defines the interface between the RAN and core networks, including the ‘A’ interface between BSC and MSC and the R-P interface between BSC and PDSN


Issue II Rev 4

cdma2000 Network Architecture


Issue II Rev 4

New Network Functions _________________________________________________________

New Network Functions Packet Control Function (PCF)

It is responsible for establishing, maintaining and releasing the interface between the RAN and PS-CN for each packet session in progress

Packet Data Serving Node (PDSN)

It keeps user profile information (from a packet data perspective), and keeps records of regarding the data usage of each user

It is the PS-CN element that interfaces with RAN. It provides routing information, routing data packets between RAN and Packet Data Network like Internet. It is similar to MSC, and also provides support for Authentication, Authorization and Accounting, which it does by interfacing with a separate AAA function

Authentication, Authorization and Accounting (AAA) function

The data mobility between different PS-CNs, cdma2000 uses Mobile IP defined by Internet Engineering Task Force (IETF). Mobile IP adds two entities, the Home Agent (HA) and Foreign Agent (FA). The HA is located in user’s home network, and anchors the user’s IP address. When the user roams into a visited network and interacts with the Packet Data Network, the Foreign Agent of the Visited network interacts with the user’s Home Agent to support packet data operation. AAA function and supported protocols and Mobile IP solution were defined by IETF


Issue II Rev 4

–Might be implemented in BSC

•AAA (Authentication, Authorization and Accounting)

New Network Functions

•PCF (Packet Control Function)

–Establishes and maintains interface between RAN and PS-CN

–Handles key auxiliary functions for packet data operation –Authentication of profile information –Authorization of data services –Collects billing information from PDSN

•PDSN (Packet Data Serving Node)

–Bridges the RAN and Public Packet Data Network –Packet Accounting –Mobile IP Foreign Agent –PPP Terminator

•Home Agent

–Function in user’s visited service area which supports Mobile IP –Often implemented on PDSN


Issue II Rev 4

cdma based 3G network _________________________________________________________

cdma2000 Based 3G Network

The network architecture for cdma2000 based wireless system still relies on the IS-41 network protocol. The IS-95 air interface has been enhanced to IS-2000 to support 3G service requirements set by ITU. IOS protocol has been enhanced as well and it also defines a new interface Radio-Packet (R-P) to support true packet data services. The BSC connects to the Packet Data Serving Node (PDSN) via the R-P interface and the PDSN connects to the Internet using Internet Protocols defined by IETF. Additional network elements can be added to support new services like location-based services.


Issue II Rev 4

cdma2000 Based 3G Network


Issue II Rev 4

cdma-RAN interfaces _________________________________________________________

cdma2000 Radio Network Interfaces

•IS-2000 air interface protocol (Mobile Station and Base Station)

•IS – 2001 (Inter Operability Specification – IOS) •A1: Signaling Interface (BS and MSC)

•A2, 5: Traffic Interface for voice and circuit data services (BS and MSC) •A3, A7: Traffic and Signaling Interfaces to support inter-system soft handoff (Source BS and Target BS)

•A8, A9: Traffic and Signaling Interfaces to support packet data services (BS and PCF). Note: While this interface has been defined, the extent to which it will be implemented remains in question. •A10, A11: Traffic and Signaling Interfaces to support packet data services (BS/PCF and PDSN)

The PDSN provides the interface to IP networks and leverages many Internet Standards such as RADIUS, Mobile IP and IPSec. The internet standards are used only for packet data services IS-41 defines the interface between different Core Network Components. The Components include MSC, HLR, VLR and AC. IS-41 is used only in Circuit Switched – Core Network (CS-CN)


Issue II Rev 4

cdma2000 Radio Network Interfaces


Issue II Rev 4

cdma2000 Network Standards

_________________________________________________________ cdma2000 Network Standards MS to Base Station (BTS/BSC)

cdma2000 Air Interface as defined in IS-2000 MS to Base Station

Point-to-Point (PPP) link between the MS (or PC) and the Packet Data Serving Node (PDSN), as defined in RFC-1661

Inter Operability Specification (IOS), as defined in IS-2001

Packet Data Serving Nod to Authentication Authorization and Accounting (AAA)

Remote access dial-in user service (RADIUS) protocol as defined in RFC 2338 and 2339

PC/MS to Packet Data Serving Node to Home Agent Mobile IP protocol as defined in RFC2002

Any of the Internet related protocols such as File Transfer Protocol (FTP), Hyper Text Transfer Protocol (HTTP), Session Initiation Protocol (SIP), Wireless Application Protocol (WAP) and so forth

Radio Link Protocol (RLP) to provide reliable link for packet data services over-the-air medium, as defined in IS-707

MS to Packet Data Serving Node

MS to MSC and BS to Packet Data Serving Node

MS to Other wireless network entities

As defined in IS-41 Packet Data Serving Node to Internet

Set of specifications as defined by the Internet Engineering Task Force (IETF)

PC/MS to Application Services


Issue II Rev 4

cdma2000 Network Standards


Issue II Rev 4

Circuit Switched Data Call

_________________________________________________________ Circuit Switched Data Call

The circuit switched architecture in cdma2000 is the same as IS-95B. The same components and architecture are used to support circuit – switched data calls. The MSC provides connectivity to circuit switched networks such as PSTN network. The circuit data path runs from the MS to BTS and then to BSC at 9.6 or 14.4 kbps. The Inter Working Function (IWF) is co-located either at BSC or at the MSC. In this example, the IWF is co-located at the MSC. The BSC is responsible for transcoding to 64kbps PCM format. The MSC sends the user traffic to IWF and IWF allocates a modem (just like a modem of a dial-up connection from home) for this call, From this point forward, the circuit – data call is similar to a dial-up connection to the Internet


Issue II Rev 4

Circuit Switched Data Call


Issue II Rev 4

Packet Data Call

_________________________________________________________ Packet Data Call

The cdma2000 networks support two IP addressing options for packet data:

1.Simple IP: Used when no mobility is required. When the MS moves from one PDSN (packet zone) to another PDSN (packet zone), the existing service/application connections are lost and the user has to reestablish those connections. For example, if the user is in the middle of downloading a web page, the user has to download the entire web page again. 2.Mobile IP: The mobile IP option is used when mobility beyond a packet zone is required. The MS may move from one PDSN (packet zone) to another PDSN (packet zone) without establishing a new service/application connection. The Mobile IP standards form IETF are used to provide packet data mobility

The cdma2000 supports high-data rate traffic channels for packet data

services. The Supplemental Channels (SCHs) introduced in cdma2000 provide a bandwidth of 307.2 kbps per channel for 1xRTT. In addition to high data rate channels, cdma2000 supports an enhanced radio state model for true packet data solutions. A new packet interface is defined between the BSC and PDSN for packet data services. The interface is known as Radio-Packet (R-P) interface


Issue II Rev 4

Packet Data Call


Issue II Rev 4

cdma2000 protocol layer

_________________________________________________________ cdma2000 Protocol Layer

IS-95 standard does not identify or specify each protocol layer separately. IS-95 covers the complete air interface specification that includes aspects of the physical layer, Medium Access Control (MAC) sublayer, Link Access Control (LAC) sublayer and upper layer. IS-2000 standard is defined as follows:

•IS-2000.1: Introduction •IS-2000.2: Physical Layer •IS-2000.3: Medium Access Layer •IS-2000.4: Link Access Control •IS-2000.5: Upper Layer Signalling •IS-2000.6: Analog Signalling

The service related to voice, circuit data and packet data are specified in separate standards. IS-707 defines service options related to data services and defines the Radio Link Protocol (RLP); a different standard, IS-127, defines Service Option 3 for Enhanced Variable Rate Codec (EVRC) voice service


Issue II Rev 4

cdma2000 Protocol Layer


Issue II Rev 4

Cdma2000 physical layer

_________________________________________________________ cdma2000 Physical Layer


Issue II Rev 4

cdma2000 Physical layer


Issue II Rev 4

Data Protection _________________________________________________________

Data Protection

Symbol Repetition

Since the wireless medium is inherently unreliable, various methods are used to protect and transfer the data .

Convolutional Encoding

Encoding increases reliability of information bits and reduces the power required for transmission. Encoded bits are called symbols. Convolutional encoders are characterized by two parameters: the constraint length (k) and the rate ( R), The constraint length refers to the number of bits used to calculate the output symbols; k=9 is used for both IS-95 and cdma2000 systems. The rate is fraction that can be seen as 1/(number of output symbols per input bit). For example, an encoder of rate ½ outputs two symbols for each input bit.

The symbols out of encoder may be repeated to achieve a particular intermediate symbol rate. For example, an encoded data rate of 4800 symbols per second might be repeated four times t achieve an effective data rate of 19.2 kbps. Each symbol could then be spread by a code consisting of 64 bits to obtain the transmission rate of 1.2288X106 chips per second. Repetition increases redundancy in the data stream

Block Interleaving

The repeated symbols are interleaved so adjacent symbols are not transmitted next to each other. This prevents adjacent data symbols from getting lost due to deep fading. It will not change effective data rate

Turbo Encoding

A turbo encoder employs two conventional encoders to increase the error correction capability, but cause some processing delays. It is added in cdma2000 to support error correction requirements for data


Issue II Rev 4

Data Protection

•IS-95

–Convolutional Encoding –Repetition –Interleaving

• IS-2000

–New: Turbo Encoding


Issue II Rev 4

Turbo Encoder

_________________________________________________________ Turbo Encoder

It is a new class of error correction codes used in digital communication systems. It is used to perform better for high data services with stringent error rate requirements of the order of 10-6 Bit Error Rates(BER). Turbo codes perform within 1db of Shannon’s limit when compared to convolutional code which perform at least 2.5 t 3.0 db short. Turbo encoder consists of two constituent convolutional encoders. Each encoder uses a 3-bit shift register with a constraint length of k=4 and encoding rate R=1/2. Both constituent encoders use the code the same data. The first encoder is fed data in the same order as input data. The second encoder uses a permuted form of the input data and the permuting is accomplished by the use of an interleaver.

•The input data bit forms the first output bit

•Each convolutional encoder outputs 2 bits for each input bit. The first constituent encoder outputs a1 and b1 symbols while the second encoder outputs a2 and b2 symbol. The cdma2000 uses different encoding rates. The defined rates are R=1/2,1/3 or 1/4 .

•R=1/2: All bits are transmitted, the first coded bits from each constituent encoder (a1 and a2) are alternately punctured to achieve the desired ½ rate

•R=1/3: All data bits are transmitted and the first encoder output bits (a1 and a2) are also transmitted to achieve the output rate of 1/3 •Rate=1/4: in this case the data bit and the first output bits of constituent encoders (a1 and a2) are always transmitted. The second output bits of constituent encoders (b1 and b2) are alternately to achieve the desired 1/4 rate.


Issue II Rev 4

Turbo Encoder


Issue II Rev 4

Channel Separation

Channel Separation

Walsh codes are a special set of orthogonal codes. Two codes are said to be orthogonal to each other if the exclusive-OR operation of the two results is an equal number of zeros and ones, I.e. cross-correlation between the two codes is equal t zero. When correlation is zero, it implies that two codes are half similar and half dissimilar to each other.

_________________________________________________________

IS-95B uses fixed 64 – bit Walsh codes for channel separation and spreading in the forward link only. In IS-2000, variable length Walsh codes are used for spreading and channel separation in both directions


Issue II Rev 4

Channel Separation

•Orthogonal Codes

–Two orthogonal codes are always half similar and half dissimilar –Inverse of an orthogonal code maintains orthogonality with other codes in the set

•IS-95B uses 64-bit Walsh codes for channel separation in the forward link •IS-2000 uses variable length Walsh codes for Channel separation in both directions •IS-2000 supports various data rates by using appropriate length Walsh codes for spreading


Issue II Rev 4

Walsh Codes in cdma2000 _________________________________________________________

Walsh Codes in cdma2000

Walsh codes are used in both forward and reverse directions to establish orthogonality cdma2000 use use reverse pilots in Reverse Link instead of Walsh modulators like in IS-95. Reverse pilots provides coherent reverse link detection

–In 95A and 95B, Walsh codes are used to establish orthogonality between channels on the forward direction only –On the reverse link in 95A and in 95B, 64-ary Walsh modulator is used to isolate Data blocks

cdma2000 supplemental channel is capable of carrying 1,036,800 bps on a single RF carrier. With the code chip rate fixed at 1228800 chips/sec, the length of the Walsh code spreading will be reduced considerably


Issue II Rev 4

Walsh codes in cdma2000 •Walsh codes are used in both forward and reverse directions to establish orthogonality •cdma2000 use use reverse pilots in Reverse Link instead of Walsh modulators like in IS-95. Reverse pilots provides coherent reverse link detection

–In 95A and 95B, Walsh codes are used to establish orthogonality between channels on the forward direction only –On the reverse link in 95A and in 95B, 64-ary Walsh modulator is used to isolate Data blocks

• cdma2000 supplemental channel is capable of carrying 1,036,800 bps on a single RF carrier. With the code chip rate fixed at 1228800 chips/sec, the length of the Walsh code spreading will be reduced considerably


Issue II Rev 4

_________________________________________________________

Walsh Covers (Reverse Link)

Walsh Covers

In the forward direction, cdma2000 uses Walsh codes to distinguish different streams of data. In the reverse direction, cdma2000 uses Walsh covers to distinguish different streams of data from the same mobile station. The base station does not assign Walsh covers; rather, they are predefined in the standard for each type of channel the mobile may want to transmit. Since the signal sent by the mobile also contains the source identification unique to each mobile, there is no conflict caused by two mobile station using the same Walsh cover at the same time. Conceptually, the base station simultaneously receiving the signal for multiple mobile stations can first use the source identification to extract the signal coming from one mobile station, and can then further extract one particular channel using the appropriate Walsh cover.


Issue II Rev 4

Walsh Covers


Issue II Rev 4

PN Codes

_________________________________________________________

PN Codes

It is generated with a register length of 42. The length of the sequence is 242-1 bits

.

Two PN codes are used in CDMA. The short PN code is used to identify each base station and the long PN code is used to uniquely identify each mobile

Short Codes

• PN code are generated using shift register of length 15. The length of sequence is 215 – 1 = 32,767 bits. •Generated at the rate of 1.2288 MHz •These codes repeat after every 26.67ms •Short codes are used for quadrature spreading in both directions •Each BS generates the same short code with a different offset that uniquely identify the base station Long Codes:

PN long code

•Generated at the rate of 1.2288 MHz •This code repeats in approximately 41 days •The long code is used for spreading in the reverse direction (MS and BS) •Each MS identify itself by altering the long code with a long code mask that is unique for each MS

•Long code masks are also used in some cases fro channel separation in the reverse direction

•In the forward direction, the long code is used for scrambling


Issue II Rev 4

PN Codes

•Short PN Codes

–Generated using a 15-shift register –Two short sequences I & Q

–Used as pilot reference signal

–Each BS assigned a unique offset of the short PN sequence

•Long PN Codes

–Generated using a 42 – bit shift register –Used for user separation in the reverse link –Long code generated using permuted ESN as the PN mask


Issue II Rev 4

Modulation

_________________________________________________________ Modulation

The cdma2000 uses Quadrature Phase Shift Keying (QPSK) to transmit data over the air in the forward direction. In QPSK, the data stream to be transmitted is divided into two streams, called the Inphase (I) and Quadrature (Q) streams. After some processing (depicted by dotted lines), the inphase stream is multiplied by a cosine wave at the carrier frequency (for example 1900MHz); the quadrature stream is multiplied by a sine wave at the same frequency. The resulting signals are combined before being transmitted. Since cos() and sin() are orthogonal functions, they can be separated at the receiver. This property allows different data to be sent simultaneously on each stream. The cdma2000 exploits this in the forward direction by allowing the data to be demultiplexed into I & Q streams, so twice as much data can be sent. In the reverse direction, different physical channels are sent on different streams. Several channels can be sent on the same stream, since they can be separated within a stream using the orthogonal Walsh covers.


Issue II Rev 4

Modulation

•Cdma2000 sends information in Quadrature streams •I&Q streams can be separated at receive r •Forward: I&Q streams can each carry one-half the data, resulting in increased Walsh code resources •Reverse: I&Q streams can each carry different channels


Issue II Rev 4

cdma2000 Forward link _________________________________________________________

cdma2000 Forward Link

The cdma2000 standard prescribes a set of “Forward Link Channel options” depending on Radio configuration scenarios. To reduce intra-cell interference, each forward link physical channel is modulated by an appropriate Walsh code or quasi-orthogonal function. Each code channel is then spread by a quadrature pair of PN sequences at a fixed chip rate of 1.2288 Mcps. Multiple Forward CDMA channels may be used within a base station in a frequency multiplexed manner. The forward link in cdma2000 essentially consists of two groups of physical channels: The common Forward Channels and the Dedicated Forward Channels The Forward Pilot Channel, Transmit Diversity Pilot Channel, Auxiliary Pilot Channels, and Auxiliary Transmit Diversity Pilot Channels are unmodulated spread spectrum signals used for synchronization by a mobile station operating within the coverage area of the base station. The Forward Pilot channel is transmitted at all times by the base station on each active Forward CDMA channel (cell or sector’s short PN offset), unless the base station is classified as a hopping pilot beacon.

If the Forward Pilot Channel is transmitted by hopping pilot beacon, then suitable timing requirements shall apply: Hopping pilot beacons change frequency periodically to simulate multiple pilot beacons transmitting pilot information This results in discontinuous transmissions on a given Forward CDMA

channel If the transmit diversity is used on a Forward CDMA channel, then the base station shall transmit a Transmit Diversity Pilot When the Transmit diversity pilot channel is transmitted, the base station should continue to use sufficient power on the Forward Pilot Channel to ensure that a mobile station is able to acquire and estimate the Forward CDMA channel without using energy from the Transmit Diversity Pilot Channel Zero or more Auxiliary Pilot Channels are transmitted by the base station on an active Forward CDMA Channel If Orthogonal Transmit Diversity (OTD) is used on the Forward CDMA channel associated with an Auxiliary Pilot Channel, then the base station shall transmit an Auxiliary Diversity Pilot


Issue II Rev 4

Forward link in cdma2000

•The forward common channels are

–The Pilot

•Common Pilot (F-CPICH) •Common Diversity Pilot (F-CDPICH •Auxiliary Pilot (F-APICH) •Auxiliary Diversity Pilot (F-ADPICH) •Dedicated Auxiliary Pilot (F-ADPICH) (Could be considered dedicated)

–The Sync Channel –The Quick Paging Channel –The Common Control Channe –The Broadcast Channel –The Common Assignment Channe l –The Common Power Control Channel


Issue II Rev 4

Pilot Channels _________________________________________________________

Pilot Channels The Pilot channels are always on Walsh Code Channel Zero and must be present in every station or sector. Pilot channels carry no information. Essentially, they consists of Short PN chips: They serve as:

•Beacon signals to facilitate rapid pilot searches by the mobiles •Demodulate reference for the Mobile Station receiver •Reference signal to define the cell boundary •Reference signal to perform handoff measurements •The shot PN code pair (PNI and PNQ) is generated by a modified linear feedback shift register. The resulting sequences have a Length of 215 or 32,768 chips. At 1.2288 Mcps, this means a period of 26.667ms •All Base Stations and Sectors use the same short code, and thus have similar pilot waveforms. They are distinguished from one another only by the phase (Short PN code Offset) of the pilot. The air interfaces stipulate that pilot phases be nominally assigned to stations in multiples of 64 chips, giving a total of 215-6=512 possible assignments. The 9-bit number that identifies the pilot phase assignment is called the Pilot Offset.

In cdma2000, five pilot channels are used. These are unmodulated spread spectrum signals and are used by MS for synchronization operating within the coverage area of a base station

–Forward Pilot Channel (F-PICH) is transmitted at all times by the base station on each active forward CDMA channel. It is covered by W064. It is similar to the pilot channel in IS-95A/B. It provides a coherent reference for easy acquisition to all mobiles in the forward link. It is used to measure the forward link and establish the cell boundary–Transmit Diversity Pilot Channel (F-TDPICH) covered by W16128–Auxiliary Pilot Channel is transmitted in beam forming application. It is covered by WnN, where N < 512 and 1<n <N-1 (Walsh code number n and Walsh code Length N are specified by the base station). –The Auxiliary Transmit Diversity Pilot Channel are transmitted when transmit diversity is used. It is covered by –An optional Auxiliary Dedicated Pilot Channel is also available It support a variety of beam forming applications and can significantly increase the capacity of the sector. It can be used with antenna beam-forming and beam steering techniques to increase the coverage or data rate towards a particular mobile station.


Issue II Rev 4

Pilot Channels

•The pilot channels are always on Walsh code channel zero and must be present in every station or sector •Short PN code pair is generated by a modified linear feedback shift register •All Base stations and sectors use the same short code and have similar pilot waveforms

Forward Pilot Channels

•In cdma2000, five pilot channels are used. These are unmodulated spread spectrum signals and are used by MS for synchronization operating within the coverage area of a base station –Forward Pilot Channel (F-PICH) is transmitted at all times by the base station on each active forward CDMA channel. It is covered by W064–Transmit Diversity Pilot Channel (F-TDPICH) covered by W16128–Auxiliary Pilot Channel is transmitted in beam forming application. It is covered by WnN, where N < 512 and 1<n <N-1 (Walsh code number n and Walsh code Length N are specified by the base station) –The Auxiliary Transmit Diversity Pilot Channel are transmitted when transmit diversity is used. It is covered by –An optional Auxiliary Dedicated Pilot Channel is also available


Issue II Rev 4

Sync Channels _________________________________________________________

Sync Channels

The sync channel (F-SYNCH) is used by mobile stations operating within the coverage area of the Base station to acquire CDMA system time and Long PN code synchronization For an omnicell coverage, there is only one Sync channel per cell. For sectored cells, there is one Sync channel per sector. For each cell or sector, the Sync Channel is a low powered, low rate (1200 bps) channel which contains a single, repeating message referred to as Sync Channel Message. This message is continuously broadcast by the cell or sector and contains parameters such as:

•The system Identification Number •The network identification number •The cell or sector’s short PN offset •The System time •The long code state •The paging channel data rate

The sync channel is covered by Walsh 32 of length 64 similar to IS-95A/B

•The bit rate for the Sync Channel is 1200bps. A sync channel frame is 26.666… ms in duration. For a given base station, the I and Q channel Pilot PN sequences for the Sync Channel use the same pilot PN sequence offset as for the Forward Pilot channel •Once the mobile station achieves pilot PN sequence synchronization by acquiring the Forward pilot channel, the synchronization for the sync channel is immediately known. This is because the sync channel (and all other channels) is spread with the same pilot PN sequence, and because the frame and interleaver timing on the Sync channel are aligned with the pilot PN sequence •The start of the interleaver block and the frame of the Sync channel shall align with the start of the pilot PN sequence being used to spread the Forward CDMA channel •For SR=1, the code speed remains at 1228800 chips/sec, frames are defined as one cycle of the short PN code, such that the Sync Frame is exactly 80/3 = 26.667 ms, equal to the period of the short code. This simplifies finding frame boundaries, once the mobile has located the pilot. Here three frames make up an 80ms superframe •The structure of the sync channel is the same as IS-95A/B implementation. Walsh code 32, of length 64 chips, is assigned to the Sync Channel for operation under Spreading Rate=1.

•The Sync Channel (F-SYNCH) is used by mobile stations operating within the coverage area of the Base Station to acquire CDMA system time and Long PN code synchronization


Issue II Rev 4

• •Sync Channel is covered by Walsh 32 of Length 64 similar to IS-95A/B


Issue II Rev 4

Idle State Common Channels _________________________________________________________

Idle State Common Channels

•The paging channel is divided into 80ms slots called paging channel slots •Paging and control messages for a mobile station operating in the non-slotted mode can be received in any of the Paging Channel Slots; •Therefore, the non-slotted mode of operation requires the mobile station to monitor all slots •The Forward Common Control Channel is divided into 80ms slots called Forward Common Control Channel slots •Paging and mobile directed messages for a mobile station operating in the non-slotted mode can be received in any of the Forward Common Control Channel slots •The overhead messages can be received on the Broadcast Control Channel •Therefore, the non-slotted mode of operation requires the mobile station to continuously monitor the Forward Common Control channel/Broadcast Control Channel •The Quick Paging Channel (F-QPCH) is used by the base station to inform the mobile stations, operating in the slotted mode while in the idle state, whether or not to receive the Forward Common Control Channel, the Broadcast Channel, or the Paging Channel •The Paging Channel (F-PCH) is used by the base station to transmit system overhead information and mobile station specific messages. Since it provides backward compatibility, it is identical to the Paging channel used in IS-95A/B •The Common control channel is a common channel used for communication of layer3 and MAC messages from the base station to the mobile station. The coding parameters are identical to those of the F-PCH. It is essentially replaces the Paging Channel for Higher Data Rates configurations (N=6,9,12) •The broadcast channel (F-BCH) is used by the base station to transmit system overhead information. (note that mobile specific or directed messages are not sent on this channel since it is a “broadcast channel”).


Issue II Rev 4

Idle State Idle Channels

•There are four Forward Common Channels that can be monitored by a MS while in Idle State:

–Quick Paging Channel (F-QPCH) –Paging Channel (F-PCH) –Common Control Channel –Broadcast Channel (F-BCH)


Issue II Rev 4

Common Control Channels _________________________________________________________

•If a Spreading Rate 1, rate ¼ coded Forward Common control channel is present, it shall be assigned to a code channel WnN, where N=16, 32 and 64 for the data rate 1 < n < N-1. The value of n is specified by the base station. •The F-CCCH shall be divided into Forward Common Control Channel slots that are each 80ms in duration. These slots shall accommodate frames that are 20,10 or 5 ms in duration

Common Control Channels

•The Forward Common Control Channel is an encoded, interleaved, spread, and modulated spread spectrum signal that is used by mobile stations operating within the coverage area of the base station. The base station uses the F-CCCH to transmit mobile station specific messages •The F-CCCH is essentially an Optimized Paging Channel for high data rate applications, so at higher spreading rates (N>3) the use of the paging channel is discontinued. The common control channel is used instead •If a Spreading Rate 1, rate ½ coded Forward Common Control Channel is present, it shall be assigned to a code channel WnN, where N=32,64 and 128 for the data rates of 38400 bps, 19200 bps, and 9600 bps, respectively, and 1 < n < N-1. The value of n is specified by the base station

•Although the data rate of the Forward Common Control channel is variable from frame to frame, the data rate transmitted to a mobile station in a given frame is predetermined and known to that mobile station


Issue II Rev 4

Common Control Channels

It essentially replaces the Paging channel for higher data rates configuration (N=6,9,12). The forward common control channel is a common channel used for communication of layer 3 and MAC messages from the base station to the mobile station. The coding parameters are identical to those of the F-PCH


Issue II Rev 4

Forward Dedicated Channels _________________________________________________________

Forward Dedicated Channels

A key limitation of IS-95A is that only one forward channel gets monitored by a mobile station at given time. Conversely, transmission made on only one reverse channel at time. In IS-95B, the use of supplemental channels running in parallel with fundamental channels meant that the mobile station is able to simultaneously transmit more than one channel. In cdma2000, transmission and by are monitoring of multiple forward channels is routine:

• Both fundamental and supplemental traffic channels are received in parallel •Like wise, the MS has to monitor the quick paging channel on an on going basis, while also reading either the paging channel or forward common control channel for example.

So, cdma2000 provides two types of forward links physical data channels –fundamental & supplemental that can each be adapted to a particular type of service. The use of fundamental & supplemental channels enables the system to be optimized for multiple simultaneous services. The two physical channels are separately coded and interleaved and in general have different transmit power levels and frame error rate set points. Each channel carries a different type of service depending on the service scenarios. This ability to transmit and receive parallel and independent data streams allows cdma2000 to achieve higher data rates. CDMA has the ability to exceed 2Mbps while retaining backward compatibility with the earlier standards.


Issue II Rev 4

Forward Dedicated Channels

•The specified forward traffic channel are: –Forward Dedicated Control Channel (F-DCCH) –Forward Fundamental Channel (F-FCH) –Forward Supplemental Channel (F-SCH) –Forward Supplemental Code Channel (F-SCCH)

•Signals transmitted on forward traffic channels are specified by radio configurations (RCs) •There are five radio configurations for the forward traffic channel •A base station shall support operation in Radio Configuration 1 or 3. A base station may support operation in Radio Configurations 2,4 or 5 •A base station shall not use Radio Configuration 1 or 2 simultaneously with Radio Configuration 3,4 or 5 on a Forward Traffic Channel


Issue II Rev 4

Forward Fundamental Channels _________________________________________________________

Forward Fundamental Channels

•The forward fundamental channel is used for the transmission of user and signalling information to a specific mobile station during a call. Each Forward Traffic Channel may contain one Forward Fundamental Channel • As in IS-95B, this channel is transmitted at variable rate (on a frame by frame basis) and consequently requires rate detection at the receiver. The F-FCHs use frame sizes of both 20ms and 5 ms depending on the required transmission objectives. •Voice must be transmitted using 20ms frames. A shorter frame would reduce one component of the total voice delay, but degrade the demodulation performance due to the shorter interleaving span •20ms frames are also the primary conveyors of data services just as they have been in IS-95A/B. In some cases, 20ms frames are also used for control •5 ms frames are used on the Forward and Reverse Fundamental Channels, but never on Supplemental channels •Each F-FCH is transmitted on a different orthogonal, variable length Walsh code channel: •Each F-FCH and F-SCCH channel with RC1 or 2 shall be assigned to a code channel Wn64, where 1 n 63 •Likewise, each F-FCH and F-DCCHI with Radio Configuration 3 or 5 shall be assigned to a code channel Wn64, where 1 n 63 •Each Forward Fundamental Channel and Forward Dedicated Control Channel with RC4 shall be assigned to a code channel Wn128, where 1 n 127. The value of n is specified by the base station

•


Issue II Rev 4

Forward Fundamental Channel

•Forward Fundamental Channel is used for the transmission of user and signalling information to a specific mobile station during a call. Each Forward Traffic Channel may contain one Forward Fundamental Channel •This channel (like in 95B) is transmitted at variable rate (on a frame-by-frame basis) and consequently requires rate detection at the receiver •Each F-FCH is transmitted on a different orthogonal, variable length Walsh code channel


Issue II Rev 4

Forward Supplemental Channels _________________________________________________________

Forward Supplemental Channels

Forward Supplemental Code Channels apply only to Radio Configurations 1 and 2 and provide backward compatibility with IS-95B. These channels are used to transmit user’s data from the base station to a mobile station during a call. When operating with Radio Configuration 1 (RC1), the Base station transmits on the Forward Supplemental Code channel using Rate Set 1 variable data rates on a frame-by-frame basis as follows:

•1200-2400-4800- and 9600 bps for RC1 (20ms frames only) •This is identical to the Rate Set 1 Reverse Traffic channel in IS-95A/B When operating with Radio Configuration2, the Base Station transmits on the Forward Supplemental Code Channel using Rate Set2 variable data rates on a frame-by-frame basis as follows: •1800-3600-7200-and 14400 bps for RC2 (20ms frames only) •This is identical with Rate Set 2 Reverse Traffic channel in IS-95A/B The forward traffic channel can simultaneously use (aggregate) up to seven supplemental code channels in order to enable higher data speeds on carriers under Rate Configurations 1 and 2


Issue II Rev 4

Forward Supplemental Channel

•The forward Supplemental Code Channels (F-SCCH) provide backward compatibility with IS-95A/B. They are defined for Radio Configurations 1 and 2 only. These channels are identical to the F-FCH operating with RC1 and RC2 (same as IS-95A/B traffic channel for Rate Set 1 and Rate Set2 respectively) •These channels are used to transmit user’s data from the base station to a mobile station during a call


Issue II Rev 4

Forward Link Radio Configurations _________________________________________________________

Forward link Radio Configurations

In the forward link IS-2000 defines nine different radio configurations: two based on IS-95B compatibility, three related to Spreading Rate 1, and four for Spreading Rate 3.

•RC1: It supports IS-95B backward compatibility for all services based on Rate Set 1 (RS1), a 9600 bps base data rate •RC2: It supports IS-95B backward compatibility for all services based on Rate Set 2 (RS2), a 14400 bps base data rate •RC3: It supports RS1-based data rates with ¼ encoding rate for Spreading Rate1 (or 1XRTT). The range of data rates supported by this configuration is from 1500 bps to 153600 bps. Orthogonal Transmit Diversity (OTD) is supported by RC3 •RC4: It supports data rates based on 9600 bps base rate and supports OTD for Spreading Rate 1 (1x). The data rates supported range from 1500 to 307200 bps •RC5: It supports data rates based on a 14400 bps base rate (RS2-based). An encoding rate of ¼ is used and RC5 supports data rates from 1800 bps to 230400 bps for Spreading Rate 1 (1X). OTD is supported by RC5 •RC6: It is for Spreading Rate 3 (3x) and it supports data rates in the range of 1500 bps to 307200 bps, based on a 9600 bps base rate. The encoding rate used is 1/6 for RC6. RC6 supports OTD and the multi-carrier deployment method •RC7: Another 3x configuration, supporting data rates from 1500 bps to 614400 bps, and like RC6, is based on a 9600 bps base rate •RC8: A 3x configuration based on RS2, with a data rate range from 1800 bps to 460.8 bps •RC9: The 3X configuration proving the highest possible rates, with a range from 1800 to 1036800 bps


Issue II Rev 4

Forward link Radio Configurations


Issue II Rev 4

Reverse Radio Configurations _________________________________________________________

Reverse link Radio Configurations

The IS-2000 physical layer standards define six different Radio Configurations (RC). These Configurations have been defined to take care of the following aspects:

•Maintaining compatibility and support for the IS-95B mobile stations and services •Adding support for services and functions using cdma2000 radio transmission technology options to increase spectral efficiency and capacity 1.25MHz channels based on Spreading Rate 1 (popularly referred to as the 1X option) •Defining and supporting use of wider-channel bandwidths (5 MHz) and allowing growth of higher-data rate support and related services This option supports the Spreading Rate 3 (also known as 3X) •In addition to these reasons, to support data rates for services based on the two currently defined and supported basic rates, each RC is defined to use both the 9.6 kbps base rate (based on Rate Set1) or the 14.4 kbps base rate (based on Rate Set 2) •Each radio configuration has associated details such as coding options, modulation options, and supported data rates that are defined as part of the IS-2000 physical layer reverse link description.

•Signals transmitted on the reverse traffic channel (reverse dedicated control channel, reverse fundamental channel, reverse supplemental channel or reverse supplemental code channel) are specified by radio configurations:

–RC1: 1200,2400,4800 and 9600 bps data rates with R=1/3. No pilot and hence, the use of the 64-ary orthogonal modulation to isolate data blocks being transmitted by the mobile –RC2: 1800,3600,7200 and 14400 bps data rates with R=1/2. No pilot and hence, the use of the 64-ary orthogonal modulation to isolate data blocks being transmitted by the mobile –RC3: 1200,1350,1500,2400,2700,4800,9600,19200,38400,76800 and 153600 bps data rate with R=1/4, 307200 bps data rate with R=1/2, BPSK modulation with a pilot –RC4: 1800,3600,7200,14400,28800,57600,115200 and 230400 bps data rates with R=1/4, BPSK modulation with a pilot


Issue II Rev 4

Reverse Link Radio Configurations


Issue II Rev 4

Reverse link Channels _________________________________________________________

Reverse link Channels

•Given a bandwidth of 1.25 MHz (for spreading rate 1) or 3.75 MHz (for spreading rate 3), the reverse link consists of various combinations of ‘code channels’ which include:

Access Channel Reverse Pilot Channel Enhanced Access Channel Reverse Common Control Channel Reverse Dedicated Control Channel Reverse Fundamental Channel Reverse Supplemental Channel Reverse Supplemental Code Channel

•Signals on the reverse traffic channels (Reverse Dedicated Control, Reverse Fundamental, Reverse Supplemental and Reverse Supplemental Code channels) are specified by their Radio Configurations (RCs). There are six Radio Configurations defined for the reverse traffic channels •A MS shall support Radio Configurations 1,3 or 5 from Rate Set 1 (1200,2400,4800 9600 bps). However, Radio Configurations 2,4 and 6 derived from Rate set2 (1800,3600,7200 and 14400 bps) are optional


Issue II Rev 4

Reverse Link Channels

•Given a bandwidth of 1.25 MHz (for spreading rate 1) or 3.75 MHz (for spreading rate 3), the reverse link consists of various combinations of ‘code channels’ which include:

–Access Channel –Reverse Pilot Channel –Enhanced Access Channel –Reverse Common Control Channel –Reverse Dedicated Control Channel –Reverse Fundamental Channel –Reverse Supplemental Channel –Reverse Supplemental Code Channel


Issue II Rev 4

Orthogonal Walsh Codes _________________________________________________________

Orthogonal Walsh Codes

•When transmitting on the R-PICH, R-EACH, R-CCCH, R-DCCH, R-FCH or R-SCH traffic with Radio Configurations 3 through 6, the mobile station uses the following Walsh codes:

Reverse Pilot Channel W032Enhanced Access Channel W28Reverse Common Control Channel W28Reverse Dedicated Control Channel W816Reverse Fundamental Channel W416Reverse Supplemental Channel-1 W12 or W24Reverse Supplemental Channel-2 W24 or W68

•Walsh code WiN represents a Walsh function of Length N that is serially constructed from the ith row of an NXN Hadamard matrix with zeroth row being Walsh code zero •So, a code channel that is covered using Walsh function ith from the N-ary orthogonal set (such as the 64X64 Walsh matrix) shall be assigned Walsh code WiN (Wi64)


Issue II Rev 4

Orthogonal Walsh Codes •When transmitting on the R-PICH, R-EACH, R-CCCH, R-DCCH, R-FCH or R-SCH traffic with Radio Configurations 3 through 6, the mobile station uses the following Walsh codes:

–Reverse Pilot Channel W032–Enhanced Access Channel W28–Reverse Common Control Channel W28–Reverse Dedicated Control Channel W816–Reverse Fundamental Channel W416–Reverse Supplemental Channel-1 W12 or W24–Reverse Supplemental Channel-2 W24 or W68


Issue II Rev 4

Gated Transmissions for RC1 and RC2

_________________________________________________________ Gated Transmissions for RC1 and RC2:

•When operating with RC1 or 2, the reverse fundamental channel interleaver output stream is time gated to allow transmissions of some Interleaver output symbols and deletion of others •The duty cycle of the transmission gate depends on the transmit data rate •For full rate transmission (9600 or 14400 bps), the “gate” allows all the interleaver output symbols to be transmitted •For half rate transmissions (4800 or 7200), the “gate” allows half of the Interleaver output symbols to be transmitted

•The “gating” process is performed by the Data Burst randomizer (DBR) •The overall objective being to reduce reverse link interference to other mobiles operating on the same CDMA carrier •When transmitting on the Access Channel, the DBR is not used. Therefore, both copies of the repeated code symbols are transmitted. (the average holding time on the access channel is very short by comparison to that on the traffic channel, so the “access state” contribution to the reverse link interference is not potentially as significant)


Issue II Rev 4

Gated Transmission

•Several types of Gated transmission strategies are used on the reverse link depending on the Mode of operation. They include:

–Variable data rate transmission on the reverse fundamental channel with radio configuration 1 and 2 (vocoder driven strategy) –PUF operation on the Reverse Traffic Channel with RC 1 and 2 –Gated operation on the Reverse Pilot Channel –Gated operation of the Enhanced Access Channel Pre-amble –Gated operation of the Reverse Common Control Channel Pre-amble


Issue II Rev 4

Quadrature Spreading RC1 and RC2

_________________________________________________________

–The In-phase and Quadrature components of the short PN have the same length of (215), the same speed (1.2288 mcps), the same phase but different generating polynomials


•The access channel and the reverse traffic channel with radio configurations 1 and 2 are spread in quadrature as follows:

–The direct sequence spreading output (Real after Long code spreading) is multiplied by a complex short PN spreading sequence

–After Quadrature Short PN spreading, the Q-channel data is delayed by half a PN chip time with respect to the I-channel data –The I-Channel data is mapped from (0,1) to (+,-), Gain-adjusted, baseband-filtered to BPSK-modulate the cos (real part) of the IF carrier –Likewise, the Q-channel is mapped from (0,1) to (+,-), gain adjusted, baseband-filtered to BPSK-modulate the sin (imaginary part) of the IF carrier


Issue II Rev 4


•The access channel and the reverse traffic channel with radio configurations 1 and 2 are spread in quadrature as follows:

–The direct sequence spreading output (Real after Long code spreading) is multiplied by a complex short PN spreading sequence –The In-phase and Quadrature components of the short PN have the same length of (215), the same speed (1.2288 mcps), the same phase but different generating polynomials –After Quadrature Short PN spreading, the Q-channel data is delayed by half a PN chip time with respect to the I-channel data –The I-Channel data is mapped from (0,1) to (+,-), Gain-adjusted, baseband-filtered to BPSK-modulate the cos (real part) of the IF carrier –Likewise, the Q-channel is mapped from (0,1) to (+,-), gain adjusted, baseband-filtered to BPSK-modulate the sin (imaginary part) of the IF carrier


Issue II Rev 4

RC Support by Mobile

_________________________________________________________ Forward-Reverse mapping of RC support by Mobile:

•A mobile station shall support operation in RC 1,3 or 5. A mobile station may support operation on RC 2,4, or 6 •A mobile station shall not use RC 1 or 2 simultaneously with RC 3 or 4 on the Reverse Traffic Channel •The Forward Link Radio Configurations are matched to the Reverse Link Radio configurations as follows: •If MS supports F-FCH with RC1, then it shall support R-FCH with RC1 •If the MS supports F-FCH with RC2, the it shall support R-FCH with RC2 •If the mobile station supports the F-FCH with RC3 and RC4, then it shall support R-FCH with RC3 •If the mobile station supports F-FCH with RC5, then it shall support the R-FCH with RC4 •If the mobile station supports the F-DCCH with RC3 or RC4, then it shall support the R-DCCH with RC3 •If the mobile station supports the F-DCCH with RC5, then it shall support the R-DCCH with RC4


Issue II Rev 4

Forward-Reverse mapping of RC support by Mobile:


Issue II Rev 4

Reverse Pilot Channel

_________________________________________________________ Reverse Pilot Channel

•The R-PICH shall be transmitted when RC 3,4,5, or 6 are enabled. (when the R-EACH, the R-CCCH, the Reverse Traffic Channel with RC3 through 6 are being used) •The R-PICH is not used for RC1 and RC2 since these configurations must be compatible with IS-95A/B which are “Pilot Less” •The R-PICH is only transmitted when the following channels are used: •Enhanced Access Channel •Revere Common Control Channel •Reverse Traffic channel •Also transmitted during the preamble of the following channels: •Enhanced Access Channel •Reverse Common Control Channel •Reverse Dedicated Control Channel •Reverse Fundamental channel

:


Issue II Rev 4

Reverse Pilot Channel •

• The reverse pilot channel is used to assist the base station in detecting mobile station transmissions

• Reverse Pilot Channel (R-PICH) [RC>2] is an un-modulated spread

spectrum signal used to assist the Base Station in detecting the Mobile Station’s transmission

• The Reverse Pilot channel [RC>2]data shall be spread with Walsh code

W032


Issue II Rev 4

Access Channel

_________________________________________________________ Access Channel

•The access channel is used by the mobile station to initiate communication with the base station and to respond to paging channel messages •The reverse access channel (R-ACH) is used by the mobile station on RCs 1 and 2 to initiate communication with the base station and respond to paging channel messages •Reverse Access channels are identified by their Long Code offsets. They use Random Access Protocol to transmit probes to the base station. In order to allow backward compatibility, the access channel is identified to the access channel specified in IS-95A/B. (The reverse pilot is not used to support the Access Channel as is the case for reverse enhanced access channels)

Reverse Access Channel

The reverse link may have up to 32 reverse access channels associated to one paging channel and information on the access channel is transmitted at a fixed rate of 4800 bps The access channel frame starts when the system time is an exact multiple of 20ms. The mobile station shall delay the transmit timing of a probe by a random delay of RN PN chips. Where RN is given by the common channel multiplex sub-layer The random delay includes the delay of the direct sequences long code of the Quadrature short PN sequences. So, it effectively increases the apparent range from the mobile to the base station. (This increases the probability that the base station isolates and demodulates incoming signals in the same access channel slot-especially when many mobiles are at a similar range from the base station) The access channel pre-amble is transmitted to aid the base station in acquiring an access channel transmission. It consists of frames of 96 zeros transmitted at 4800 bps •


Issue II Rev 4

Reverse Access Channel

•The reverse link may have up to 32 reverse access channels associated to one paging channel and information on the access channel is transmitted at a fixed rate of 4800 bps •The access channel frame starts when the system time is an exact multiple of 20ms. The mobile station shall delay the transmit timing of a probe by a random delay of RN PN chips. Where RN is given by the common channel multiplex sub-layer •The random delay includes the delay of the direct sequences long code of the Quadrature short PN sequences. So, it effectively increases the apparent range from the mobile to the base station •The access channel pre-amble is transmitted to aid the base station in acquiring an access channel transmission. It consists of frames of 96 zeros transmitted at 4800 bps


Issue II Rev 4

Access Channel

_________________________________________________________ Enhanced Access Channel

•The enhanced access channel (REACH) replaces the access channel for higher radio configurations. Like access channel, it is used by the mobile station to get the Base station’s attention or to respond to base station messages in Radio configurations 3-4. •There are three modes of operation of the channel:

Basic Access Mode:

The mobile station does not transmit the Enhanced Access header. An access probe consists of an Enhanced Access Channel Preamble followed by data

Power controlled access mode:

Here, an Enhanced Access Channel probe consists of a preamble, the Enhanced access channel header and the data

Reservation Access mode: Here, the probe consists of two parts only: The preamble and the Enhanced Access Channel header. When permission is given for the reservation, the actual data is transferred using the Reverse Common Control Channel. (In other words, the R-EACH sets up the R-CCH to do the work) Reverse Access channels are identified by their Long code offsets covered by Walsh code W28. They use Random Access Protocol to transmit probes to the base station. In order to facilitate the detection process at the base station, the reverse pilot is transmitted during the Enhanced Access Channel Probe.


Issue II Rev 4

Enhanced Access Channel

•The enhanced access channel is used by the mobile station with RC3 through RC6, to initiate communications with the Base station or to respond to mobile-directed messages •The enhanced access channel (REACH) replaces the access channel for higher radio configurations •There are three modes of operation of the channel:

–Basic Access Mode –Power controlled access mode –Reservation Access mod e

•Reverse Access channels are identified by their Long code offsets covered by walsh code W28


Issue II Rev 4

Reverse Enhanced Access Channel _________________________________________________________

Reverse Enhanced Access Channel

•The reverse link may have up to 32 reverse enhanced access channels associated to one Forward Common Control Channel. (Not to the paging channel as per IS-95A. The F-CCH takes over the Paging Channel functions for RC3 thru 6. R-EACH (Not Access channels) are also enabled for RC3 thru 6. In a way, Paging channels are to access channels what the F-CCCH are to the R-EACH) •Enhanced Access Channel Headers are transmitted at a fixed rate of 9600 bps while the actual access data is transmitted at a fixed data rate of 9600 bps, 19200 bps or 38400 bps depending on transmission goals (QoS). (For last access requirements, the 38400 bps data transmission rate may be used for example) •The frame duration for an Enhanced Access Header shall be 5ms. The frame duration for the Enhanced Access data shall be 20ms, 10ms or 5ms. The timing of Enhanced Access Channel transmissions starts on 1.25ms increments of system time.


Issue II Rev 4

Reverse Enhanced Access Channel

•The reverse link may have up to 32 reverse enhanced access channels associated to one Forward Common Control Channel •Enhanced access channel headers are transmitted at a fixed rate of 9600 bps while the actual access data is transmitted at a fixed data rate of 9600 bps, 19200 bps, or 38400 bps depending on transmission goals (QoS) •The frame duration for an Enhanced Access header shall be 5ms. The frame duration for the enhanced access data shall be 20ms, 10ms or 5 ms. The timing of enhanced access channel transmissions starts on 1.25ms increments of system time


Issue II Rev 4

Reverse Common Control Channel

_________________________________________________________ Reverse Common Control Channel

•In IS-95A, the Access Channels are complementary to the Paging channel. There could be up to 32 access channels associated to one Paging Channel •Likewise, the Reverse Common Control Channels (R-CCH) are complementary to the Forward Common Control (F-CCH). Up to 32 R-CCH could be associated to a F-CCH. Note that the Forward Common Control channel is an optimized Paging Channel for higher data rate requirements (N>3). In these applications, it is used for signalling and user data when traffic channels are not in use •Just as the F-CCH is an optimized Paging channel, the R-CCH is an optimized Access channel for higher data rate applications. Each Reverse Common Control Channel is associated with a single forward common control channel. Frame sizes of 20ms, 10ms and 5 ms are used •There are two modes of operation for the R-Common Control Channel •Reservation Access Mode •Designated Mode •The reverse link may have up to 32 Reverse Common Control channels associated to one Forward common control channel and up to 32 reverse common control channels associated to one Forward Common Assignment channel. Each reverse common control channel is associated with a single forward common control channel •The MS transmits on the Reverse common control channel at variable data rates 9600 bps, 19200 bps and 38400 bps depending on transmission requirements •The frame duration for an Enhanced Access Header shall be 5 ms. The frame duration for the enhanced access data shall be 20ms, 10ms or 5ms. The timing of enhanced access channel transmission starts on 1.25ms increments of system time


Issue II Rev 4

Reverse Common Control Channel •This channel is used for the transmission of user data and signalling information to the base station when the reverse traffic channels are not in use •Revere common control channel can operate in one of two modes:

–Reservation Access mode or –Designated access mode –The MS transmits during designated, reserved, intervals of time specified by the base station

•Reverse common control channels are identified by their Long Code offsets. They use Random Access Protocol to transmit probes to the base station. In order to facilitate the detection process at the base station, the reverse pilot is transmitted during the enhanced access channel probe


Issue II Rev 4

Reverse Dedicated Control Channel _________________________________________________________

Reverse Dedicated Control Channel

•The reverse dedicated control channel is used to carry user data as well as signalling and control information while the call is in progress •The reverse traffic channel may contain up to one dedicated control channel •The Mobile transmits on the reverse dedicated control channel at a fixed data rate 9600 bps or 14400 bps using 20ms frames or 9600 bps using 5ms frames •For RCs 3 & 4, the 9600 bps speed is used with 20ms frames. For Radio configurations 4, the 14400 bps speed is used with 20ms frames •For RC 3 and 4, the 9600 bps speed is used with 5ms frames:

–9600 bps with a 20ms frame (RC3) –14400 bps with a 20ms frame (RC4) –9600 bps with a 5ms frame (RC3 and RC4)


Issue II Rev 4

Reverse Dedicated Control Channel

•The reverse dedicated control channel is used to carry user data as well as signalling and control information while the call is in progress •The reverse traffic channel may contain up to one dedicated control channel •The Mobile transmits on the reverse dedicated control channel at a fixed data rate 9600 bps or 14400 bps using 20ms frames or 9600 bps using 5ms frames •For RCs 3 & 4, the 9600 bps speed is used with 20ms frames. For Radio configurations 4, the 14400 bps speed is used with 20ms frames •For RC 3 and 4, the 9600 bps speed is used with 5ms frames:

–9600 bps with a 20ms frame (RC3) –14400 bps with a 20ms frame (RC4) –9600 bps with a 5ms frame (RC3 and RC4)


Issue II Rev 4

Reverse Fundamental Channel

_________________________________________________________ Reverse Fundamental Channel

•The reverse fundamental channel is used to carry voice, signalling and low rate data during a call. Basically it will operate at low FER (around 1 percent). It supports basic rates of 9.6 kbps and 14.4 kbps and their corresponding sub-rates (Rate set 1and 2 of IS-95) •The reverse fundamental channel does not operate in a scheduled manner; thus permitting the mobile station to transmit acknowledgements or short packets without scheduling. This reduces delay and the processing load due to scheduling. Its main difference compared to the IS-95 voice channel is that discontinuous transmission is implemented using repetition coding rather than gated transmission •Unlike reverse supplemental channels, only one reverse fundamental channel can be used by the mobile station during a call.


Issue II Rev 4

Reverse Fundamental Channel

•The reverse fundamental channel is used to carry voice, signalling and low rate data during a call. Basically it will operate at low FER (around 1 percent). It supports basic rates of 9.6 kbps and 14.4 kbps and their corresponding sub-rates (Rate set 1and 2 of IS-95) •The reverse fundamental channel does not operate in a scheduled manner; thus permitting the mobile station to transmit acknowledgements or short packets without scheduling. This reduces delay and the processing load due to scheduling. Its main difference compared to the IS-95 voice channel is that discontinuous transmission is implemented using repetition coding rather than gated transmission •Unlike reverse supplemental channels, only one reverse fundamental channel can be used by the mobile station during a call

.


Issue II Rev 4

Data Rates

_________________________________________________________ Reverse Fundamental channel Data Rates

•When operating with RC1, the MS transmits on the Reverse fundamental channel using Rate Set1 variable data rates on a frame-by-frame basis •When operating with RC1 and RC3, the MS transmits on the Reverse Fundamental Channel using variable data rates derived from Rate Set 1 on a frame-by-frame basis •1500-2700-4800 and 9600 bps for RC3 (20ms frames and 5ms frames) •1500-2700-4800 and 9600 bps for RC5 (20ms frames and 5ms frames) •This is identical to the Rate Set1 Reverse Traffic channel in IS-95A/B •When operating with RC2 and RC4, the MS transmits on the Reverse Fundamental Channel using Rate Set 2 variable data rates on a frame-by-frame basis •1800-3600-7200 and 14400 bps for RC2 (20ms frames) •1800-3600-7200 and 14400 bps for RC4 (20ms frames and 5ms frames) •This is identical to the Rate Set 2 Reverse Traffic Channel in IS-95A/B •Note1: RC1,RC2,RC3 and RC4 are defined for SR1, that is with the use of one 1.25 MHz frequency carrier. RC5 and RC6 are defined for SR3 and require a BW of three times the basic 1.25MHz block •Note2: While the lower rate config (RC1 & RC2) use 20ms frames, the higher rate config (RC3 thru RC6) use 5ms frames as well as 20ms frames. The use of 5ms frames allows fast packet transmission •Note3: The data rate and Frame duration on a Reverse Fundamental Channel within a RC are selected on a frame-by-frame basis. However, for data rates below 7200 bps, the modulation symbol rate is kept constant by the Repetition device


Issue II Rev 4

Reverse Fundamental channel Data Rates

•When operating with RC1, the MS transmits on the Reverse fundamental channel using Rate Set1 variable data rates on a frame-by-frame basis •When operating with RC1 and RC3, the MS transmits on the Reverse Fundamental Channel using variable data rates derived from Rate Set 1 on a frame-by-frame basis •When operating with RC2 and RC4, the MS transmits on the Reverse Fundamental Channel using Rate Set 2 variable data rates on a frame-by-frame basis


Issue II Rev 4

Reverse Supplemental Code Channel _________________________________________________________

Reverse Supplemental Code channel

•When operating with RC1, the MS transmits on the Reverse Supplemental Code Channel using Rate Set1variable data rates on a frame by frame basis

•1200-2400-4800 and 9600 bps for RC1 (20ms frames only)

•Reverse supplemental code channels apply only to RC1 & 2 and provide backward compatibility with IS-95B. They are used to transmit user’s data to the base station during a call

•This is identical to the Rate Set1 Reverse traffic channel in IS-95A/B •When operating with RC2, the MS transmits on the Reverse Supplemental Code Channel using Rate Set2 variable data rates on a frame by fame basis •1800-3600-7200 and 14400 bps for RC2 (20ms frames only)

•This is identical to the Rate Set 2 Reverse Traffic channel in IS-95A/B •The reverse traffic channel can simultaneously use (aggregate) up to seven supplemental code channels in order to enable higher data speeds on carriers under RC1 and 2


Issue II Rev 4

Reverse Suuplemental Code Channel

•Reverse supplemental code channels apply only to RC1 & 2 and provide backward compatibility with IS-95B. They are used to transmit user’s data to the base station during a call •When operating with RC1, the MS transmits on the Reverse Supplemental Code Channel using Rate Set1variable data rates on a frame by frame basis •When operating with RC2, the MS transmits on the Reverse Supplemental Code Channel using Rate Set2 variable data rates on a frame by fame basis •The reverse traffic channel can simultaneously use (aggregate) up to seven supplemental code channels in order to enable higher data speeds on carriers under RC1 and 2


Issue II Rev 4

cdma2000 channel summary ________________________________________________________

cdma2000 Channel Summary

List of Forward channels in cdma2000 is given in the page opposite


Issue II Rev 4

Forward Channel Summary


Issue II Rev 4

cdma2000 channel summary _________________________________________________________

cdma2000 Channel Summary

List of Reverse channels is given in the page opposite

The differences between IS-95 and cdma-2000 is given in the appendix


Issue II Rev 4

Reverse Channel Summary


Issue II Rev 4

Packet Switched call Setup

__________________________________________________________ Packet Switched call setup

MS initiates packet data session by an Origination Message to the network. It is followed by access authentication. The air interface resources for the packet service are set up using the following steps:

•The Radio Setup using messaging defined in the IS-2000 standard for cdma2000. The MSC-BS call setup using messaging defined in IS-2001 (IOS). The packet data service connect using messaging defined in IS-2000 standard for cdma2000. The Radio Link Protocol (RLP setup using messaging defined in IS-707-A-1.10. •The BS sets up an R-P session with PDSN using messaging defined in IS-2001 (IOS). The R-P messaging is based on Mobile IP messaging •After BSC opens R-P interface connection, the PDSN initiates the PPP link between PDSN and the MS. The link is established and configuration is negotiated using Link Control Protocol (LCP) – RFC 1661. •Following PPP connection the MS initiates a Mobile-IP based mobility connection with the Home Agent •The Packet data core network authentication procedure is performed between AAA and either the PDSN or MS. This authorizes the Mobile user to the PDSN resources to connect to the Internet •Finally, the mobile user is able to exchange packet user traffic with any entity on the Internet


Issue II Rev 4

Packet Switched Call Set up


Issue II Rev 4

Future of cdma2000 __________________________________________________________

Future of cdma2000

Some of the key goals of 3G are build on the success of 2G systems by offering more voice capacity and supporting packet data services such as Internet access. Some the services, such as multimedia, require 3G systems to offer data rates in excess of 2 Mbps Voice and circuit based services (fax and async data) require low throughput where as packet data services are asymmetric in nature, where the demand of the forward link is much greater than the reverse link. The data services are bursty in nature and can tolerate some degree of latency Some 3G systems like UMTS and 1x cdma2000 support both voice and packet data services with the same network and radio interface. 3G systems such as 1xEV-DO support only data services. 1xEV-DV supports voice and packet data services by employing the same network and radio interface


Issue II Rev 4

–Support more voice users

–Support voice and data services simultaneously

–Voice: Low speed, symmetric, low latency, uniform QoS

Future of cdma2000

•3G (IMT-2000) Requirements

–Support Packet Data Services simultaneously –Support Packet Data Service at ˜ 2 Mbps data rate

• Voice and high speed packet data impose vastly different requirements

–Packet Data: High burst rates, asymmetric, variable latency, non-uniform QoS


Issue II Rev 4

Capacities and limitations __________________________________________________________

Capacities and Limitations of cdma2000 and IS-95

1xcdma2000 support higher voice capacity and support efficient packet-based access to Internet services including multimedia services. The data rates in 1x are limited to 614.4 kbps. So, certain services such as video conferencing are not possible in 1x systems. Cdma2000 does provide 3x configuration to support data rates up to 2Mbps. However, the complexity associated with the 3x configuration has made it practically obsolete even before it is developed

IS-95 wireless networks are deployed in North America and South America and some parts of Asia. IS-95(cdmaOne) support primarily voice, low rate services like SMS, 14.4 kbps data services It doesnot support packet-based access to Internet and other multimedia services.

The cdma2000 standard is published as IS-2000 which consists of three revisions. Rev0 is the baseline version. Rev A enhances Rev0 by defining new radio channels for paging and spectral efficiency. RevB specifies minor changes over RevA.


Issue II Rev 4

Capacities and Limitations of cdma2000 and IS-95


Issue II Rev 4

1X Evolution Alternatives __________________________________________________________

1X Evolution Alternatives

Two solutions have been designed for evolution from 1x systems. These are 1xEV-DO (1x Evolution for Data only) and 1xEV-DV(1x evolution for data and voice). Both solutions are designed for optimized packet data services and data rates exceeding 2 Mbps 1xEV-DO systems were pioneered by Qualcom. They are known as High Rate Packet Data (HRPD) systems in 3GPP2 and are defined in the standard IS-856 in TIA. 1xEV-DO systems are designed as an add-on to 1x systems. They operate in a separate 1.25 MHz carrier from 1x systems so service providers are required to dedicate a separate 1.25 MHz carrier for them. More over 1xEV-DO systems support non-real-time packet data services only. The mobile terminal uses 1x carrier for voice and circuit data services and 1xEV-DO carrier for packet data services. 1xEV-DO is not backward compatible with 1x. That is a separate standard 1xEV-DV systems are designed as evolution to 1x systems. As such, they work seamlessly with 1x systems. In fact, the standard for 1xEV-DV is published as IS-2000 Rev C. IS-2000 Rev C is a specification for both 1xEV-DV and 1x systems. 1xEV-DV is 100% backward compatible with 1x systems.


Issue II Rev 4

1X Evolution Alternatives


Issue II Rev 4

Goals of 1XEV-DV __________________________________________________________

Goals of 1x EV-DV

The important goal of 1xEV-DV is to support optimized packet data services at data rates exceeding 2 Mbps. At the same it has to be backward compatible with the existing 1x systems. Therefore, it is designed to operate in the 1.25MHz channel which is the bandwidth used for 1x systems. 1xEV-DV supports voice and packet data services simultaneously. This is required to support multimedia and Voice over IP services. This is key difference between 1xEV-DV and 1xEV-DO systems since 1xEV-DO systems support only non-real-time data services. For voice services, the service provider has to rely on 1x systems but 1xEV-DO and 1x systems operate on different 1.25MHz carriers. Since the mobile terminal is not built to track both 1x and 1xEV-DO carriers, it cannot support simultaneous voice and high speed data services. 1xEV-DV systems are built to support voice and packet in the same 1.25 MHz bandwidth. Therefore, the mobile terminal can obtain simultaneous voice and packet data services at 2 Mbps from the same carrier.


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Goals of 1x EV-DV


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Overview of 1X EV-DO _________________________________________________________

Overview of 1x EV-DO

The 1xEV-DO air interface is specially designed to serve non real time packet data services where the service demand is intermittent and bursty. One single shared channel is time multiplexed among all the users to support bandwidth on demand. The 1xEV-DO air interface occupies a 1.25 MHz frequency band, same as IS-95 or cdma2000 1x system. By employing higher-level modulation (QPSK, 8-PSK and 16-QAM) it is able to deliver high data rates up to 2 Mbps.

In 1xEV-DO based wireless network, the 1xEV-DO Radio Access Network (BTS/BSC) does not communicate with MSC. The 1xEV-DO only terminal will not be able to access circuit switched services. The hybrid terminal monitors the cdma2000 common channels to receive paging related messages while exchanging user traffic on 1xEV-DO system


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Overview of 1X EV-DO

•Only for non real-time packet data •Occupies 1.25 MHz frequency (same as cdma2000 1x system) to deliver>2Mbps data rate •Fixed power variable rate •No connection to MSC (CS-CN) •To PDSN: Type of terminal (cdma2000 or 1xEV-Do) is transparent •Hybrid AT monitors cdma2000 common channels (for possible Page of SMS) while exchanging data with 1xEV-DO system


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The data rates 1xEV-DV systems exceed 3MBps for packet data services. 1xEV-DV achieves this by employing spectrally efficient optimizations. But there is no improvement in voice capacity. The network interfaces including IOS and IS-41 are minimally impacted by 1xEV-DV. 1xEV-DV retain signalling mechanisms and call model of 1x systems

Overview of 1X EV-DV __________________________________________________________

Overview of 1x EV-DV

1xEV-DV meets IMT2000 data rate requirements by supporting data rates in excess of 2 Mbps for packet data services. It is backward compatible with the existing 1x systems It supports voice, real-time data and non-real time data service in the same 1.25MHz carrier


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•Support 3G requirements of IMT-2000 while being backward compatible to 1x

•No/Minimal impact to IOS Packet Interfaces

Overview of 1X EV-DV

–Voice, circuit data, packet data (real and non real-time)

•Voice and data users simultaneously on a single 1.25MHz band •Enhanced 1x Air Interface

–3.09 MBps peak data rate in forward link –Maintains call model of IS-95 and 1x –Spectrally efficient compared to 1x

•Voice capacity is same as 1x •No change in reverse link data rates


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Overview of 1X EV-DO Network Architecture _________________________________________________________

Overview of 1x EV-DO Network Architecture

The diagram given in the next page shows enhancements made to basic 1xEV-DO system. These enhancements are required to support access authentication and interface between two access networks. The AN-AAA server is added to the access network authentication. The interface between AN-AAA server and BSC is A12. This interface is based on RADIUS protocol The interface between BSC of two different access networks is A13. This is an IP based interface In addition, the 1xEV-DO network includes A8-A11 interfaces that are defined as part of basic IOS document.


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Architecture of 1X EV-DO


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Overview of 1X EV-DV Network Architecture

__________________________________________________________ Overview of 1x EV-DV Network Architecture

The basic architecture is unchanged from 1x systems. The biggest change is the 1xEV-DV air interface between the mobile station and the BTS/BSC. The BTSs and the BSC together form the radio network. The circuit switched network is anchored by the PDSN. It consists of AAA servers, the HA and FA. The interface between BSC and CN is defined in the IOS. IOS defines interfaces between BSC to PDSN, BSC to MSC and BSC to BSC in a series from A1 through A11


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EV-DV Architecture


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Migration from 2G to 3G __________________________________________________________

Migration from 2G to 3G

2.5 G solutions provide inherent support for packet data, medium data rates and a lower cost evolution from 2G than jumping directly to 3G For CDMA2000 networks the first phase called 1X or 1XRTT(Radio Transmission Technology) can only get up to 614.4 Kbps max-higher than GPRS/EDGE. 3G technologies can go as high as 2Mbps and will develop in two phases. Phase 1 involves high speed packet data operations while still supporting voice and circuit switched data through the circuit switched core network. Phase 2 involves purely IP operations, carrying even voice over the IP network.


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Migration from 2G to 3G


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Migration Paths to 3G __________________________________________________________

Migration Paths to 3G

Motorola plans to gradually evolve the network toward a packet IP model. The following section provide an overview of all the features and services that will be offered during the phases. Services will continue to be offered via the existing circuit-based components in addition to the introduction of the packet based elements

• cdma2000 1X: An evolution of current IS95A/B to increase voice capacity up to 2 times and increase peak data rates up to 10 times, achieving 144kbps to 153.6kbps

• IS95A to IS95B

• 1XEV-DO (1X Evolved Data Only): An evolution of IS95A/B and cdma2000 1X systems to offer Data only capabilities at twice the capacity

• 1XEV-DV (1X Evolved Data Voice): An evolution of IS95A/B cdma1X and 1XEV-DO systems to maximize both peak and rates and data capacity while maintaining the ability to offer 1X voice services

Data Rates: CdmaOne 2G: IS95A =14.4 Kbps 2.5G: IS95B=64kbps 3G: 1X:95C:cdma2000:IS2000=144kbps/153.6kbps 1X-EV-DO = 620kbps 1XEV-DV=1.2Mbps


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Migration Paths to 3G


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Release Timelines

__________________________________________________________ Release Timelines


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Release Timelines


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1X Network Overview __________________________________________________________

1X Network Overview

The diagram given in the page opposite details simplified CDMA network. Each network component is illustrated only once, however, many of the components will occur several times throughout a network. Each network component is designed to communicate over an interface specified by SCTM Motorola protocol. This provides flexibility and enables a network provider to utilize system components from different manufacturers. For example, a Motorola BSS equipment may be coupled with a Cisco system

The Principal components of a CDMA network are given below

The Mobile

This consists of the mobile telephone, fax machine etc. This is the part of the network that the subscriber will see.

The Switch

This consists of the Mobile Switching Center (MSC). This is the part which provides for interconnection between the CDMA network and the Public Switched Telephone Network (PSTN)

This supports provisioning of 3G data subscribers Packet Data Network

This supports evolution towards an IP-based, peer-to-peer network, providing circuit and packet data components

The Radio Access Network

This is the part of the network which provides the radio interconnection from the mobile to the land based switching equipment

The Network Management Center

This enables the network provider to configure and maintain the network from a central location.

The Intelligent Network (Not Shown)


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!X Overview


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Mobile Station __________________________________________________________

The Mobile Station

The mobile is the hardware used by the subscriber to access the cellular network. The mobile is programmed with information regarding the service the subscriber should receive. The subscriber is identified by a Mobile Identification Number (MIN) or International Mobile Subscriber Identity (IMSI). This number is unique for the particular device and permanently stored in it. The IMSI identifies the mobile subscriber. It is only transmitted over the air during initialization.The MIN enables the network operator to identify mobile equipment which may be causing problems in the system. This is the telephone number of the mobile subscriber. It is comprised of a country code, a network code, and a subscriber number. Calls are routed and billing is performed based on the identity of the subscriber and its equipment or its location. The mobile is capable of operating at a certain maximum power output dependent on its type and use. The mobile station is the only part of the CDMA network which the subscriber will really see. There are two main types of MS, these are listed below.

•Vehicle Mounted-These devices are mounted in a vehicle and the antenna is physically mounted on the outside of the vehicle. •Hand portable Unit-This equipment comprises of a small telephone handset not much bigger than a calculator. The antenna is connected to the handset.

1X Mobile Technology

•Cellular (824.025-848.985MHz) and PCS bands (1850-1910MHz) with Spreading Rate 1 (1.25 MHz).

•IS95 A/B only •1X only with voice/data

•1X with voice only (no data) •IS95 A/B voice/data and 1X voice/data


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The Mobile Station


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Radio Access Network __________________________________________________________

Radio Access Network

The key elements of Radio Access Network are

• Centralized Base Station Controller (CBSC) • Access Network Node (AN) • Base Transceiver Station (BTS)


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Radio Access Network


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Centralized Base station Controller __________________________________________________________

Centralized Base Station Controller Introduction

The Centralized Base Station Controller (CBSC) combines the control, network interface and transcoding functions into one logical entity, the CBSC. To accomplish this, the CBSC consists of the Transcoder (XC) and the Mobility Manager (MM) interconnected by the Access Node (AN) and Token Ring (fiber). The Transcoder primarily provides voice encoding and decoding functions. The MM provides a high performance, high availability platform for call processing and mobility management software applications.

Functions The main functions of the CBSC are:

•Manage the radio channels •Transfer signaling information to/from mobile stations •Speech encoding and decoding •Control of the BTS and XC components •Perform call processing and mobility management •Perform operations and maintenance •Each CBSC can support 1-150 BTSs •One CBSC and all of the BTSs under its control make up a Base Station System (BSS)

Mobility Manager (MM)

The MM provides the central processing unit for the CBSC. It also supports several I/O protocols that are used to communicate with the other entities in the system. Call processing and operations and maintenance software is executed on the MM. It is a main component in the system overload control strategy. The MM provides the radio channel control functions and all call setup and teardowns via software loaded on this platform. The channel control software works in conjunction with the call processing software in the MSC.

Circuit Inter-Working Unit (IWU) The circuit IWU in Motorola’s CDMA architecture provides the subscriber the ability to exchange asynchronous data, Quick Net Connect, and facsimile transmission. The IWU is attached to the XC and becomes an integral part of the CBSC. CDMA data transmissions provide superior accuracy. It utilizes two error correction and retransmission protocols, Radio Link Protocol (RLP) and Transmission Control Protocol (TCP), which guarantee error free delivery of data. The various data services, such as rate selection, are initiated as service options during call setup. The IWU’s digital modems support the V.42 protocol, which provides (flow control) rate adaptation to the landline modems. The IWU supports synchronous and asynchronous data services, which emulate a traditional modem connection to the PSTN.


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CBSC


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Transcoder __________________________________________________________

Transcoder (XC) The transcoder provides variable rate vocoder speech coding/decoding for calls as specified in IS-95. The transcoder serves as an interface to circuit-based networks such as the MSC, Circuit IWU, and circuit-based CBSCs.The main functions of the XC are:

•Transcoding of voice (Pulse Code Modulation (PCM) to/from Code Excited Linear Predictive (CELP). Transcoding function supports the physical channel conversion of PCM from the MSC to CELP for the BTS •Span line termination for subrate circuit BTS connections •Switching of voice traffic between BTS sites, the internal transcoder functionality and the MSC •Soft handoff selection function for circuit traffic Packet Subrate Interface (PSI). Controls handoffs between cells or sectors •Support for 16Kbps SC Transcoder Rate Adaption Unit (STRAU) frame sub-rate timeslot packaging •Maintains correct RF output power levels for each mobile station •Circuit switching of BTS signaling/control and data •Combining of multiple voice paths during soft handoff, called frame selection. Found only in CDMA systems •Support legacy inter-CBSC soft handoff connectivity to Motorola circuit-based CBSCs •Provide connectivity to the Circuit IWU for circuit data calls, including Quicknet Connect calls

Base Transceiver Station (BTS) The BTS provides the air interface to the mobile station. BTSs can be used in omni, 3 or 6 sector configurations.

Operations and Maintenance Center - Radio (OMC-R) The OMC-R provides operation and maintenance for up to 8 CBSCs. The three types management are possible

:•Database Management •Fault Management •Performance Management

Universal Network Operations (UNO) UNO provides a centralized point from which operators have access to the data and interfaces needed for network administration. UNO uses Graphical User Interfaces (GUIs) to manage cellular networks. UNO focuses on three management areas:

•Status Management •Alarm Management •Performance Management

System Monitoring Application Processor (SMAP) SMAP is a tool for the optimization of new or existing CDMA networks, as it maximizes your current system’s performance. Through a logical GUI, SMAP helps you monitor system RF performance, enabling you to optimize, maintain and troubleshoot your CDMA system.


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CBSC


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Access Node __________________________________________________________

Access Node (AN) Overview

The Access Node (AN) is a key element introduced in system release G16.0. It serves as the transport focal point to interconnect the local network elements within the RAN for delivery of control and bearer traffic. The AN provides a BTS span aggregation point and enables packet switching between CBSC network elements. Standard routing protocols track all possible paths through the network. Via routing table updates, the routing protocol continually tracks the most efficient path to the network destination. The AN is capable of terminating various physical interfaces including 10/100BaseT ethernet and gigabit ethernet interfaces.The AN is comprised of the following:

•Aggregation Node (AGNODE) - Cisco MGX8850 multiservice Switch is responsible for the aggregation of a large number of backhaul span lines. •Multi Layer Switch (MLS) - Cisco CAT6509 multilayer LAN switches, or IP switch, is a layer 2 (Datalink)/layer 3 (Network) switched Ethernet router responsible for the routing of all control, bearer, and O&M traffic within the IP RAN.

The main functions of the AN are:

•BTS span aggregation point •Routing of all control, bearer, and O&M traffic within the IP RAN


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Access Node


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Base Transceiver Station __________________________________________________________

Base Transceiver Station (BTS)

The BTS provides the air interface connection with the Mobile Station.

•Contains RF Hardware •Limited Control Functionality •Each BTS will support omni (1), 3 or 6 cells/sectors.

Configurations

CBSCs may control several BTSs, the maximum number of BTSs which may be controlled by one CBSC is not specified by CDMA. Individual manufacturer’s specifications may vary greatly. Motorola’s maximum number of BTSs is 150. The BTSs and CBSC may either be located at the same cell site “Co-located”, or located at different sites “Remote”. In reality, most BTSs will be remote, as there are many more BTSs than CBSCs in a network. Another BTS configuration is the Daisy Chain. A BTS need not communicate directly with the CBSC which controls it, it can be connected to the CBSC via a chain of BTSs. Daisy chaining reduces the amount of cabling required to set up a network as a BTS can be connected to its nearest BTS rather than all the way to the CBSC. Problems may arise when chaining BTSs, due to the transmission delay through the chain. The length of the chain, must, therefore, be kept sufficiently short to prevent the round trip speech delay becoming too long.


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BSS Configurations


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1X BTS __________________________________________________________

1X Base Transceiver Station (BTS)

Motorola’s BTS portfolio for cdma2000 1X includes the SC4812T series and the SC300 series BTS platforms. The SC4812T family includes the indoor SC4812T, the outdoor 2-cabinet/4-carrier SC4812ET, and the SC4812ET Lite, an outdoor two-carrier minicell. The SC300 series is Motorola’s microcell and picocell solution for cdma2000 1X. Simple FRU, field replaceable unit, facilitates the migration to cdma2000 1X or to future cdma2000 air interface technologies.

Supporting BTSs

The following frame types will support cdma2000 1X capability:

•SC300 •SC4812T •SC4812ET •SC4812 Expansion Frame •SC4812ET Lite (New)

Local Maintenance Facility (LMF)

Computer using Windows graphical user interface (GUI) for:•Initial optimization/calibration/ATPs of BTS•Perform maintenance on BTSThe upgraded LMF will provide calibration of the devices while the site remains in - service. For this purpose:

•Directional couplers must be installed in-line with the RF paths at each site. •Sites equipped with RFDS will have directional couplers installed. •Sites already equipped with RFDS will need to be upgraded to become 1X compatible


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1X BTS

BTSs- SC300- SC4812T- SC4812ET- SC4812ET Lite•

BTS

Support-LMF


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Packet Data network __________________________________________________________

Packet Data Network Why a PDN?

The purpose of the Packet Data Network (PDN) is to provide connectivity for subscribers accessing servers and applications that reside on the Operator’s internal IP network, that reside in external private networks (e.g. external corporate intranets), and that reside in the external public ISP networks. The operator’s IP network resembles an Internet Service provider’s (ISP) network with the addition of some key network elements that are specifically designed to enable mobile, wireless Internet access from CDMA RANs. Those key network elements are:

•Packet Data Serving Node (PDSN) •Authentication, Authorization and Accounting (AAA) Server •Home Agent (HA) Routers

The diagram illustrates the logical network model for the IP network, which is compliant with the Wireless IP Network reference model described TR45.6 or IS-835 specifications.


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Packet Data Serving Node _________________________________________________________

Packet Data Serving Node (PDSN) The PDSN is introduced in G16.0. It provides the interface between the CBSC, specifically the packet control function (PCF) and the Data Network. For a Mobile-IP system, the PDSN supports the functions of Mobile IP Foreign Agent and facilitates the authentication of the mobile station (MS) as specified in the Mobile IP standard. So far, two types of PDSNs have been selected:

•3com Model TC1000 (shown) •Cisco Model 7206

With the Motorola architecture, the operator shall enjoy the integration of all previous packet data functionality on the PDSN. This includes support of IS-95A and IS-95B data services. In the case of CDMA Circuit Switched Data, the current Circuit Data inter-working unit (IWU) is required for each CBSC. The PDSN is suitable for both facilities with current deployed packet IWU installations as well as a build out of new packet data capability. The PDSN is interoperable with existing packet IWU devices and corresponding RADIUS AAA servers while providing increased access rates and additional aggregate data capacity for packet data subscribers over current packet IWU capabilities. For installations where the PDSN replaces circuit IWU functionality the PDSN provides this functionality without increasing the load on the MSC. The PDSN is only applicable to CDMA systems and applies to packet data calls. A PDSN can handle the data calls of several CBSCs. It is logically connected to the PSI-PCF (Packet Control Function) of the CBSC, via the AN, and can be connected with up to 200 PSI-PCFs. A 100BaseT Ethernet connects the PDSN to the CBSCs via Access Node (AN). The Ethernet connection provides the capability to connect multiple CBSCs to a single PDSN or have multiple PDSNs supporting a single CBSC. In addition to the packet forwarding, the PDSN performs subscriber authentication and collects accounting data and forwards it to the accounting server. The authentication is performed during the PPP negotiation that occurs between the PDSN and the mobile station. The network of PDSNs is responsible for ensuring that all traffic addressed to an MS is correctly delivered. Data can be received either from external IP Networks or from other PDSNs in the Mobile Operator’s Data Network. This is accomplished by using the concept of a " Home Agent " and a " Foreign Agent ". All traffic destined for a MS is automatically routed to the MS's " Home Agent " as though the MS were attached to the " Home Agent ". The " Home Agent " encapsulates the data and forwards it to the current serving Foreign Agent or PDSN, where it is de-encapsulated and transferred to the MS.


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PDSN


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AAA Server _________________________________________________________

Authentication, Authorization and Accounting (AAA) Server

The AAA Server is also introduced in G16.0 and provides authentication, authorization and accounting services.

•Authentication is the verification of a subscriber’s identity through a verification of per-determined credentials such as user id and password. •Authorization is the determination of access privileges to networks or network services based on the authenticated identity of a requester. •Accounting involves the collection and correlation of resource usage for the purpose of billing, auditing, cost allocation or performance analysis.

To minimize the possibility of fraudulent usage, a subscriber authentication mechanism is typically required for a Packet Data Network. The authentication mechanism consists of a two-part authentication procedure. 1.The subscriber’s mobile station is authenticated to ensure that the subscriber has a valid mobile.2.Then authentication of the subscriber’s data terminal equipment. This allows the network to verify that the user has established data services and to allow the Service Provider to perform accounting/billing for network services provided. As the subscriber begins the air interface data access procedures, the mobile station is authenticated from the MSC/VLR/HLR using a modification of existing authentication procedures. At the successful conclusion of this authentication sequence, the data communication device is authenticated utilizing methods defined in either the Mobile IP or Simple IP specification.


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AAA Server


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Home Agent

Home Agent (HA)

•Mobile IP subscribers

The Home Agent maintains the location of the mobile through mobile registrations and forwards or redirects data (packets) to the Foreign Agent (internal to the PDSN) where the mobile is currently registered.

_________________________________________________________

The Home Agent (HA), also introduced in G16.0, is a separate network element within the PDN that enables mobility management for:

•Simple IP subscribers

Introduced in G16.0, the Home Agent (HA) is a mobility agent located in the home network that provides routing functionality for registered mobile stations. The HA maintains the network attachment location information of a mobile station, which is known as mobility binding. Also, the HA tunnels packets destined for a mobile while the mobile is attached to a visitor network. Mobiles that support Mobile IP functionality are assigned a HA and a home IP address which they are known to other mobiles and applications on the Internet or Intranet. The Home IP address allows other mobile devices and applications to reach the mobile while the mobile is connected to the network. Mobile IP utilizes the HA to track the location of the mobile when it roams out of the home network, and for-wards the Home Agent to the Foreign Agent serving the mobile. The PDSN will support Simple IP registration with a HA for Simple IP capable mobiles to facilitate mobility across different PDSN serving areas within the same Access Network. When the mobile is not in the home network, it will register with the serving PDSN or Foreign Agent (FA). The mobile looks at advertisements from local routers to deter-mine whether the serving PDSN supports the options required by the mobile. Once this is determined, the mobile will send a care-of-address issued by the PDSN called a collocated care-of-address, or it can use the FA’s IP address, referred to as the foreign agent care-of-address. If Mobile IP is supported by the mobile host, then it will register on the HA with the care-of-address from the FA and the options it would like for it registration. If Simple IP is supported by the mobile host, the FA serving the mobile host will register with the HA. For G16.0 Cisco routers will be used to implement the HA function, and will be connected via an IP network to the PDSN. The HA is expected to have a capacity of 1 million packets per second, which will include 1500 FA/HA tunnels, or 225,000 bindings.


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Home Agent


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Network Operations and Maintenance Description _________________________________________________________

Network Operations and Maintenance Description:

The Network Operations and Maintenance solution for the cdma2000 1X network is an integration of OMC building blocks each of which was designed and developed to serve the specific needs of the elements of its domain. Through integration efforts Motorola and its partners are able to provide a distinct advantage in operability and cost of operations, over other competing solutions. The key components of this solution are:

•OMC-R •OMC-IP •UNO

With the integration of packet based architectures of IP within the traditionally circuit based architectures of mobile systems a new paradigm of network management is being created. These two technologies have management methodologies that are different in many ways and this new combination will most likely require changes in the methodologies of the organizations that have traditionally supported them. In order to facilitate customers in adapting to the changes that are expected, Motorola and its partners are offering a management solution that strives to provide the best mixture of the management styles of Telecommunication and IP. The most significant offering is the integration of the alarm, trap, and event streams of all of the managed devices into a single data stream for the operator. Integrated device configuration schema allows provisioning tasks that impact both the radio and the packet network, to be executed from a single location with a minimal number of user actions. The operator can access all of the applications needed to do his job from a single user’s station. This is achieved by utilization of consistent hardware and operating systems across the various products of the OMC, and by endorsing the utilization of web based applications wherever possible.


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Operations and Maintenance Center - Radio _________________________________________________________

Operations and Maintenance – Radio (OMC-R) The OMC-R is a highly available UNIX-based O&M platform that supports the core components of the CDMA Radio Access Network (RAN), including the Central Base Site Controller (CBSC), the Base Transceiver Stations (BTS), and Internet Protocol (IP) components for circuit and packet networks. The OMC-R acts primarily as a data collection and mediation device for alarms, events, statistics, and configuration.The main functions of the OMC-R are:

•Repository of software images and configuration databases •Control and status of the RAN elements •Controls the execution of RFDS loopback and forward/reverse power tests •Temporary storage of performance management and call detail log data •Collection of alarms and event data

Operations and Maintenance – Internet Protocol (OMC-IP) The Operations and Maintenance Center – IP, or OMC-IP, is a new introduction to the CDMA Network Operations, Planning and Optimization solution for the cdma2000 1X initial deployment in system release G16.0. The OMC-IP is a logical suite of functionality that consists of an integrated solution of Sun Microsystems server platforms, Cisco element managers, Motorola software and other third party applications. The primary function of this OMC-IP is to provide Element Management capabilities for the Cisco technology domains including Layer 2 (Datalink) switching and Layer 3 (Network) Internet Protocol (IP) enabling components of the cdma2000 1X Access Node (AN), Packet Data Service Node (PDSN), AAA and HA.The Cisco element management systems are mature commercial products with added mobile wireless features. The two primary components of this solution are:

•Cisco System’s Cisco WanManager (CWM) •CiscoWorks for Mobile Wireless (CW4MW).

These two pieces of software provide for the customer the element management control needed to manage and troubleshoot the Cisco network elements that make mobile IP a possibility in the cdma2000 1X solutions.These software components also provide the integration with Motorola’s Radio Access Network (RAN) management solutions (OMC-R and UNO) needed to make the management of this new architecture an easier task for the cellular network operator .


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Network Operations and Maintenance


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Universal Network Operations _________________________________________________________

Universal Network Operations (UNO)

The Motorola Universal Network Operations (UNO) system is an open network management system designed to provide the centralized point from which operators have access to the data and interfaces needed for network administration.UNO’s user interfaces are standards based Graphical User Interfaces (GUIs) built upon the latest technologies, including web-supporting JAVA applications.The management areas that UNO is focused on are

•Device status management •Alarm management •Performance management •Configuration management

Additional UNO applications support operators in tasks as diverse as access to on-line system documentation, RFDS loop-back test scheduling and analysis, element software distribution, Call Final Class (CFC) analysis, load analysis for element processors, etc.


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Network Operations and Maintenance


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Motorola cdma2000 network Migration _________________________________________________________

Motorola cdma2000 1X network Migration Motorola’s cdma2000 1X implementation is based upon a migration strategy that leverages operator’s investments in IS-95A/B infrastructure. Future demands are dictating the coexistence of IS-95A/B and cdma2000 1X systems. Motorola’s solution for cdma2000 1X includes a graceful migration from IS-95A/B to cdma2000 1X that integrates existing circuit based equipment within a new IP based architecture. Motorola’s cdma2000 1X solution is an IP Radio Access Network (RAN) connected to an IP Packet Data Network (PDN). This architecture incorporates existing 2G components into a new IP packet-based transport network. New components are added to support the IP transport network and connections to other packet data networks.

IP-RAN The IP packet-based approach offers a flexible architecture with significant growth capabilities and a graceful integration into other networks. The IP architecture is highly scalable and offers reduced costs compared to other technologies. The open interface nature of IP allows for ease of integration of future network elements and services. In addition, the IP architecture allows the network to more closely follow the performance curves of worldwide IP development efforts. Motorola’s migration strategy to an IP RAN integrates the IP components with minimal risk and minimal disruption to the existing 2G voice centric network. Current investments in voice services are protected while the operator gains experience with new packet services. This is accomplished by first adding new IP components to support new 1X data capabilities and services to the existing 2G network. Once the IP transport network is fully integrated and proven stable voice and 2G services are moved over to the IP transport network thereby completing the migration from a subrate circuit architecture to an IP architecture. This approach is achieved by system releases G16.0 and G16.1. System release G16.0 is a full cdma2000 1X solution that has minimal impact to existing voice and 2G services. Voice and 2G services remain on a subrate circuit transport network while new 1X data services are integrated into the network over a new IP transport network.

Release G16.0 •1.5 to 2 times voice capacity increase over IS-95A/B •User data rates of up to 144Kbps •Enable new revenue generating services such as Internet web access and Multimedia •Minimize risks to existing services such as voice •Introduce packet components-IP-RAN-Packet Data Network •Investment protection by re-using existing equipment within the G16 architecture •Up to 1800 Erlangs per CBSC


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G 16.0 System Diagram


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APPENDIX A

Data Burst Randomization Algorithm


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_________________________________________________________ The data burst randomizer uses a block of 14 bits used in the long code .

These 14 bits are from the long code spreading bits used in the last but one Power control Group. To put it differently, these bits ocur exactly one PCG before the boundary of every Reverse Traffic frame.

o

o

o

o

Let the 14 bits be “ b0...........b13 ”. Here, b0 and b13 are the oldest and earliest bits respectively. The randomization algorithm used depends on the data rate, as described below:

• Full Rate ( 9600 ): o All the 16 PCGs are active.

• Half Rate ( 4800 )

Only 8 out of the 16 PCGs are active. The following rule applies: PCG no. = b0;b1 + 2; b2 + 4; b3 + 6

b4 + 8;b5 + 10; b6 + 12;b7 + 14.

• Quarter Rate ( 2400 ): Only 4 of the 16 PCGs are active. The following rule applies. PCG no. = b0 if b8 is 0 or b1 + 2 if b8 is 1

b2 + 4 if b9 is 0 or b3 + 6 if b9 is 1 b4 + 8 if b10 is 0 or b5 + 10 if b10 is 1 b6 + 12 if b11 is 0 or b7 + 14 if b11 is 1

One-Eighth Rate ( 1200 ) Only 2 of the 16 PCGs will be active. The following rules apply.

PCG No. =b0 if b8 and b12 = 0 or b1 + 2 if b8 = 1,b12 = 0 b2 + 4 if b9 = 0, b12 = 1 or b3 + 6 if b9 = 1,b12 = 1 b4 + 8 if b11 = 0,b13 = 0 or b5 + 10 if b10 =1,b13 = 0 b6 + 12 if b11 = 0, b13 = 1 or b7 + 14 if b11 =1,b13 = 1

The PCGs that will be acive for the different data rates for b0 to b13 combination given below as an example are shown in the diagram opposite.

b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b131 0 0 1 1 1 0 1 1 0 1 0 0 1


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b0 to b13 are assumed to be : 1 0 0 1 1 1 0 1 1 0 1 0 0 1 b0 b13

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

9600

4800

2400

1200


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APPENDIX B

CALL PROCESSING – IMPORTANT PARAMETERS


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Call Processing in CDMA _________________________________________________________

Important Parameters

ACC_CHANSNumber of Access channels supported by the current paging channel. (stored in mobile’s temporary memory)

ACC_MSG_SEQS Last received access parameter message sequence number.

CURR_ACC_MSG_SEQ Current Access parameter message sequence number.

CDMACHSThe CDMA channel number currently used by the mobile. CHAN_LST_MSG_SEQ “CDMA channel list” message sequence number. CONFIG_MSG_SEQ Current message sequence number for the System Parameters Message, Neighbour list message, CDMA channel list message, Extended system Parameters message and Global Redirection message. MAX_REQ_SEQ Maximum number of access probe sequences for an Access channel request. (1-15) MAX_RSP_SEQ Maximum number of access probe sequences for an Access channel response. ( 1-16 )

MAX_SLOT_CYCLESMaximum value of slot cycle index allowed by the current base station.

MIN_P_REVS: Minimum mobile station PROTOCOL revision level that is required for the mobile to access the CDMA system.


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Important Parameters

P_REV

MSG_REQ_ACKSNext message sequence number for messages requiring acknowledgment.

MSG_SEQ+NOACKSNext message sequence number for messages that DO NOT require an acknowledgment.

NGHBR_CONFIGS Neighbour base station channel allocation

NGHBR_PNSNeighbour base station Pilot Channel PN sequence offset in units of 64 PN chips.

NIDSNetwork identification.

PAGECHS Current Paging Channel number

PAGE_CHANSNumber of Paging channels supported by the current CDMA channel.

PILOT_PNSPilot PN sequence offset for a base station, in units of 64 chips.

PRATSData rate of the Paging Channel

SProtocol revision supported by the base station.

PWR_REP_FRAMESSPower control reporting frame count; The number of frames over which the mobile has to count frame errors. ( 1-15 )

PWR_REP_THRESHOLDSPower control reporting threshold; The number of bad frames ( 1- 32 ) to be received in a measurement period before the mobile generates a Power Measurement Report Message.


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Important Parameters PWR_STEPSPower increment for successive access probes.

Current value of the CDMA system time as received in the Sync Channel Message.

SIDSSystem Identifier

SID_NID_LISTS The SID/NID pair in which the mobile is registered.

SLOT_CYCLE_INDEXSEqual to SLOT_CYCLE_INDEXP OR the received maximum slot cycle index, WHICHEVER is SMALLER. SLOT_NUM Paging channel Slot number

SRCH_WIN_AS Search window size for the ACTIVE SET and the CANDIDATE sets. (These sets will be explained shortly).

SRCH_WIN_NS Search window size for the Neighbour set.

SRCH_WIN_RS Search window size for the Remaining set. SYS_PAR_MSG_SEQ System parameters Message sequence number.

SYS_TIMES

T_ADDS Pilot Detection Threshold.

T_COMPS Active Vs Candidate set comparison threshold. T_DROPS Pilot Drop Threshold. TOT_FRAMESS :

Total number of frames received; counted for forward channel power control.


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APPENDIX C

IS-95 VS cdma2000


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Phisical Channels

Deployment of Configurations


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Packet Data Support

Services Support


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Frames and Encoding

Power Control


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Other Differences

High Speed Packet Data


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Spectral Efficiency

The cdma2000 uses both convolutional and turbo encoders. Convolutional encoders used for voice and for data rates of up to 14.4 kbps. For high-speed data, turbo encoders are preferred. IS-95B power control was based on the assumption that CDMA was limited by capacity and interference on the reverse link. As a result IS-95B supports fast closed loop power control (800 power control commands per sec) in the reverse direction only. The power control for the forward direction is much slower (50 or fewer times per second). But forward link is the limiting factor for capacity because of the high powered base stations. In cdma2000, a fast forward closed loop power control scheme is introduced to address this problem. Forward link power control is done at the rate of 800Hz, the same rate as the reverse link fast power control scheme. Collisions occur when multiple mobiles transmit over the same access channel in IS-95B. Each time there is a collision, the MS increases its transmit power. This results in increased interference, which reduces the capacity of the cell. The cdma2000 introduces the concept of reservation during system access to avoid the problem of collision. The cdma2000 introduces reverse pilot channels to enhance the reverse link performance. IS-95B does not have a pilot channel in the reverse direction. Reverse pilot channels enable the base stations to coherently demodulate signals the MSs, which in turn helps in reducing the transmit power requirements of the mobile stations.


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Notes


Cdma 02 Finalsdda

Documents

frequencies local loop

local exchange

cdma concept

concept of cdma

principles of cdma page

features of cdma

advantages of cdma

cdma standardsintroduction