Principles of the WCDMA System.ppt

HUAWEI TECHNOLOGIES CO., LTD.

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Huawei Confidential

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Principles of the WCDMA System

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 2

Preface

Now, the most popular term in the mobile

communication field is WCDMA!

What is WCDMA? And what is its benefit?

Today, let’s go to know about WCDMA!


Contents

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA

FDD

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential 4

WCDMA Releases

UMTS Release 99

UMTS Release 4

UMTS Release 5

UMTS Release 6

• UMTS CN = enhanced GSM NSS• UTRAN & WCDMA

• Bearer independent CS domain• Low chip rate TDD mode• UTRA repeater• MMS• LCS enhancements• etc.

• IP Multimedia Subsystem (IMS)• RNC connectivity to multiple CN nodes• HSDPA• etc.

1999

2001

2002

2003• WLAN-3GPP feasibility study• Network sharing feasibility study• Security enhancements• Push services• etc.

WCDMA =UMTS = DS-CDMA3G – WCDMA , CDMA2000 , TD-SCDMA


What’s New in WCDMA?

Multiservice Environment

Data speed

Bit rate varies from 4.75 kbps up to 384 kbps

Variable bit rate also available

Service delivery type

Real-time (RT) & non real-time (NRT)

Quality classes for user to choose

Different error rates and delays

Traffic asymmetric in uplink & downlink

Common channel data traffic

Inter-system handovers

Multiservice Environment

Data speed

Bit rate varies from 4.75 kbps up to 384 kbps

Variable bit rate also available

Service delivery type

Real-time (RT) & non real-time (NRT)

Quality classes for user to choose

Different error rates and delays

Traffic asymmetric in uplink & downlink

Common channel data traffic

Inter-system handovers

Air Interface

• Capacity and coverage coupled - “cell breathing”

• Neighbour cells coupled via interference

• Soft handover

• Fast power control

• Interference limited system (e.g. GSM frequency limited)

Air Interface

• Capacity and coverage coupled - “cell breathing”

• Neighbour cells coupled via interference

• Soft handover

• Fast power control

• Interference limited system (e.g. GSM frequency limited)

Characteristic to WCDMA• RAKE receiver takes advantage of multipath propagation• Fast power control keeps system stable by using minimum power necessary for links• Soft handover ensures smooth handovers

Characteristic to WCDMA• RAKE receiver takes advantage of multipath propagation• Fast power control keeps system stable by using minimum power necessary for links• Soft handover ensures smooth handovers

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WCDMA Network ArchitectureCN (Core Network)

circuit switched (cs) domain

packetswitched (ps) domain

MSC/VLR

SGSN

UTRAN (UMTS Terrestrial Radio Access Network)

RNC

Node B

Node B

RNC Radio Network Controller UE User Equipment

RNC

Node B

Node BRadio

Network Subsystem

(RNS)

Iub

Iub

IurIu-PS

Iu-CS

Uu

UEHLREIR AC

GMSC

GGSN

PSTN/ISDN

Internet


RNC Tasks and Functions

• WCDMA radio resource management Admission Control, Packet Scheduling, Load Control, Power Control, Handover Control, Resource Manager.

• Telecom functionalityincl. Location & connection management (Transport Manager), ciphering, Iu and Iub channel management, ATM switching and multiplexing

• Maintenanceincl. Fault localisation and reconfiguration

• Operationincl. RNC and Node B parameter modification


Node B Tasks and Functions

101010010101010001

Iub InterfaceATM

Uu InterfaceWCDMA

Cellular Transmission managementManaging ATM switching and

multiplexing over the Iub interface. Control of AAL2/AAL5 connections. Control of the physical transmission

interfaces – E1, PDH, SDH or microwave.

Air Interface management. Controlling Uplink and

Downlink radio paths on the Uu Air Interface. Baseband to RF

conversion. Antenna multi-coupling.

O&M Processing.

Interfacing with NMS and RNC for alarm

and control (Operations and Maintenance)

functions.

Radio Channel functions.Transport to physical channel mappings. Encoding/Decoding – Spreading/Despreading user

traffic and signalling.

RNC


3G Spectrum Allocation


3G Terms IMT 2000 (International Mobile Telephony)

Third generation mobile systems as defined by ITU (International Telecommunications Union)

Global recommendation 3GPP

3rd Generation Partnership Project (Forum for a WCDMA standardization) Involved: ETSI (Europe), ARIB (Japan), TTA (Korea), T1P1 (USA), TTC (Japan)

and CWTS (China) UMTS (Universal Mobile Telecommunication Services)

Third generation telecommunication system, that is subject to specifications produced by 3GPP

WCDMA Air Interface technology adapted for UMTS Terrestrial Radio Access (UTRA)

UTRA-FDD WCDMA in 3GPP, FDD mode

UTRA-TDD WCDMA in 3GPP, TDD mode

CDMA2000 Air Interface technology proposal from TR45.5 (USA) on evolution of IS-95 (CDMA)


Duplex Technology – Distinguish User’s UL and DL Signal – FDD

Frequency division duplex (FDD) : Distinguish the uplink and

downlink according to the frequencies. Adopted by the WCDMA, CDMA2000 and GSM

Advantage: It can be easily implemented.

Disadvantage: The spectrum utilization is low when the uplink and

downlink services (mainly the data services) are asymmetrical.


Duplex Technology – Distinguish User’s UL and DL Signal – TDD

Time division duplex (TDD) : Distinguish the uplink and downlink

according to the timeslots. Adopted by the TD-SCDMA

Advantage: The uplink and downlink can be allocated with different numbers

of timeslots when the uplink and downlink services are asymmetrical.

Therefore, the spectrum utilization is high.

Disadvantage:

− It cannot be easily implemented and needs precise synchronization. In the CDMA

system, GPS synchronization is needed.

− When it is used with the CDMA technology, it is difficult to control interference

between the uplink and the downlink.


Traffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000

Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS

Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM

Multiple Access Technology - Distinguish Different Users

FrequencyTime

Power

FDMA

User

User

User User

User

FrequencyTime

Power

TDMA

Power

Time Frequency

CDMA


Characteristics of CDMA System

High Spectral Efficiency

Frequency multiplex coefficient is 1.

Soft capacity

Quality

Coverage

Interference

Self-interference system

A UE transmission power is interference for another UE.

Wideband system


WCDMA = DS-CDMA

WCDMA is a code-division multiple access technology which separates each

user’s voice or data information by multiplying the information by pseudo-random

bits called "chips".

The pseudo-random bit sequences have a rate of 3.84 Mcps (millions of chips

per second), resulting in the narrowband information bits of the user being spread

across a much wider bandwidth of approximately 5 MHz.

For this reason, CDMA technology is sometimes referred to as “spread

spectrum.”

The user data (signal) is first spread by the channelisation code (based on

Hadamard matrix) called Orthogonal Variable Spreading Factor (OVSF) Code.

OVSF code has the property that two different codes from the family are

perfectly orthogonal if in phase


Common Terms

Bit, symbol and chip

Bit (bps): the data that is obtained upon source coding and contains

information.

Symbol (sps): the data obtained upon channel coding and interleaving.

Chip (cps): the data obtained upon final spreading.

− The spreading rate of WCDMA is: 3.84 Mcps

Processing gain

It refers to the ratio of the final spreading rate to the bit rate (cps/bps).

In the WCDMA system, the processing gain depends on the specific

service.


Processing gain (Gp)Gp = Wc/Wi

Where Wc: chip rate

Wi: user data rate

The more processing gain the system has, the more the power of uncorrelated interfering signals is suppressed in the despreading processThus, processing gain can be seen as an improvement factor in the SIR (Signal to Interference Ratio) of the signal after despreadingExample: Voice AMR 12.2 Kbps Gp = 10*log(3840000/12200)= 25 dBAfter despreading the signal power has to be typically few dB above the interference and noise: Eb/No = 7dB;

therefore the required wideband signal-to-interference ratio is 7dB – Gp = -18 dB.In other words, the signal power can be 18dB under the interference and the WCDMA receiver can still detect the signalWideband signal-to-interference ratio is also called carrier-to-interference ratio: C/I Thanks to spreading and desporeading, C/I can be much lower in WCDMA than GSM (C/I = 9-12 dB)

f

Wi

Wc


Basic Diagram of the WCDMA System

Source coding

Channel coding and interleaving

ScramblingSpreading ModulationRF

transmission

Source decoding

deinterleavingChannel

decoding and de-interleaving

De-scramblingDe-spreading DemodulationRF

reception

Radio link


Source Coding in WCDMA

The WCDMA system adopts the adaptive multi-rate (AMR) speech coding. A total of eight coding modes are available. The coding rate ranges from 12.2

Kbps to 4.75 Kbps.

Multiple voice rates are compatible with the coding modes used by current mainstream mobile communication systems. This facilitates the design of multi-mode terminals.

The system automatically adjusts the voice rate according to the distance between the user and the NodeB, thus reducing the number of handovers and call drop.

The system automatically decreases the voice rate of some users according to

the cell load, thus saving power and containing more users.

Source coding

InterleavingChannel coding and interleaving


transmission


Spreading Factor and Service Rate

Chip rate = symbol rate spreading factor

For WCDMA, if the chip rate is 3.84 MHz and the spreading factor is 4, the

symbol rate is 960 Kbps.

For CDMA2000-1x, if the chip rate is 1.2288 MHz and the spreading factor is

64, the symbol rate is 19.2 Kbps.

Symbol rate = (service rate + check code) × channel code ×repetition

or punching rate

For WCDMA, if the service rate is 384 Kbps and the channel code is 1/3

Turbo, the symbol rate is 960 Kbps.

For CDMA2000-1x, if the service rate is 9.6 Kbps and the channel code is

1/3 convolutional code, the symbol rate is 19.2 Kbps.


Spreading in WCDMAConsists of 2 operations:1. Channelization• Transforms each symbol (data bit) to the number of chips (increases

bandwidth)• Number of chips per symbol = Spreading Factor (SF)2. Scrambling• Scrambling code is applied

Data

Bit Rate

Channelization code (OVSF)

Chip Rate Chip Rate

TX

Scrambling Code


OVSF & WalshOrthogonal Variable Spreading Factor

OVSF codes (Walsh) are completely orthogonal and their mutual correlation is zero.

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

Spreading Factors (FDD mode):• UL: 4, 8, 16, 32, 64, 128, 256• DL: 4, 8, 16, 32, 64, 128, 256, 512 The spreading factor can be changed every TTI (10, 20, 40, or 80 ms).


Why CDMA system is a self interference system?

Since all the users use orthogonal code, where does the self

interference come from?

Comes from the code error during the transfer.

If there are some code error on one user’s information, it

misses some orthogonal to others. Then interference comes.


Scrambling in the WCDMA System

Downlink: Different cells (sector carrier frequencies) have

different downlink scrambles.

Each cell is configured with a unique downlink scramble. The UE

identifies a cell based on the scramble.

The OVSF code is used to differentiate different users in a cell.

Uplink: Scrambles are used to differentiate different users.

In a cell, each user is configured with a unique uplink scramble.

The OVSF code is used to differentiate the services of a user.

Source coding

InterleavingChannel coding and interleaving


transmission


Usage of the codes

Channelization Code Scrambling Code

Usage Uplink: separation of physical data (DPDCH) and control channels (DPCCH) for the same terminal

Downlink: separation of downlink connections to different users within on cell

Uplink: Separation of terminals

Downlink: Separation of sectors (cells)

Length 4-256 chips

In downlink also 512 chips

Uplink: 10ms = 38400 chips

Downlink: 10ms = 38400 chips

Number of codes Spreading Factor indicates the number of codes under one scrambling code

Uplink: over 16 millions

Downlink: 512

Code Family Orthogonal Variable Spreading Factor (OVSF)

10ms code: Gold Code

66.7μs code: Extended code family

Spreading Yes, indicates bandwidth No, does not affect bandwidth


Summary - Advantages of CDMA RAKE receiver is adopted

The time diversity effect generated by channel coherence time is efficiently used.

Frequency diversity

Wideband frequency spectrum

Higher interference tolerance and security performance

Low signal transmission power

Great flexibility in carrying multiple services with largely different bit rate and QoS requirement.

Different spreading factors for different services with different data rates

High spectral efficiency

All users can share the same frequency spectrum simultaneously.

Supporting soft handover and softer handover.


Contents

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA

FDD


WCDMA System Characteristics W-CDMA : 5 MHz Carrier Spacing : multiples of 200 kHz Carrier Spacing : 4.4 – 5.4 MHz W-CDMA spreading rate = 3.84 Mchip/s Chip Rate = 3.84 MHz

Uplink and downlink modulation: QPSK/QPSK Information bit rate: between 4.75 kbit/s and 2 Mbit/s (currently up to 384 Kbit/s) Spreading Factor (SF): 4 -256 Multiple Access Scheme : Wideband DS-CDMA Duplex Scheme : FDD and TDD modes 10 ms frame with 15 time slots Voice coding: AMR (Adaptive Multi-Rate) NodeB synchronization: asynchronous Highly variable data rates, data rate constant within 10 ms frame Bandwidth on demand, efficient resource usage Multiple services with different variable data rates over one physical channel

Segment A Segment B Segment C

5 MHz


Satisfy the minimum performance requirement of IMT2000

Compatible with GSM-MAP core network

Comparatively steady version R99 has been released

Support open loop and closed loop transmit diversity mode

Support Common Packet Channel(CPCH) and Downlink

Share Channel, adapt to Internet data access mode

Support macro diversity, selection diversity of NodeB

location

Support different fast power control algorithms and open

loop, out loop power control

Fully support UE locating services

WCDMA System Characteristics


Key features of WCDMA

Soft handoff: user equipment (UE) and base stations use special rake receivers that allow each UE to simultaneously communicate with multiple base stations. The diversity gain associated with soft handoff is known as the "soft handoff gain factor".

Multipath reception: the rake receivers also allow the UE to decode multiple signals that have traveled over different physical paths from the base station. For example, one signal may travel directly from the base station to the UE, and another may reflect off a large building and then travel to the UE. This phenomenon, "multipath propagation", also provides a diversity gain. The same effect occurs on the uplink from the UE to the base station.

Power control: transmissions by the UE must be carefully controlled so that all

transmissions are received with roughly the same power at the base station. If power control is not used, a “near-far” problem, where mobiles close to the base station over-power signals from mobiles farther away, occurs. The base station uses a fast power control system to direct the mobile to power up or power down as its received signal level varies due to changes in the propagation environment. Likewise, on the downlink, transmissions from the base stations are power-controlled to minimize the overall interference throughout the system and to ensure a good received signal by the UE.


Key features of WCDMA

Frequency reuse of 1: every base station in the CDMA system operates on the same frequency for a given carrier, so no frequency planning is required. As every site causes interference to every other site, careful attention must be paid to each site's radio propagation.

Soft capacity: capacity and coverage are intertwined in CDMA, depending on the number of users in the system and the amount of interference allowed before access is blocked for new users. By setting the allowed interference threshold lower, coverage will improve at the expense of capacity. By setting the threshold higher, capacity will increase at the expense of coverage. Because of the fundamental link between coverage and capacity, cells with light traffic loads inherently share some of their latent capacity with more highly loaded surrounding cells.


WCDMA Compared to GSM and CDMA IS-95 WCDMA vs. GSM

WCDMA has some similarities with GSM technology, however, it is a fundamentally different technique for allowing multiple users to share the same spectrum and as a result it has many differences.


WCDMA Compared to GSM and IS-95 CDMA


Adopts AMR voice coding and supports the voice quality of 4.75

Kbps to 12.2 Kbps.

Adopts soft handover and transmit diversity to improve

capacity.

Provides high-fidelity voice modes.

Supports fast power control.

Voice Evolution in WCDMA


Supports up to 14.4 Mbps data services – HSDPA and HSUPA

Supports packet switching.

Can evolution to All-IP structure.

Provides QoS control.

Provides mobile IP services (dynamic assignment of IP addresses)

Provides high quality support for symmetric uplink and downlink data services, including the voice, videophone and video conference.

Data Evolution in WCDMA


Conclusion This course describes the WCDMA system.

This course first describes some key technologies. Then,

describes the basic principles of CDMA and the WCDMA

FDD mode.

After studying this course, we can have a preliminary

understanding of WCDMA, thus laying a good foundation for

subsequent study.

Thank You !www.huawei.com

Principles of the WCDMA System.ppt

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