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3GCNCDMA2000 Core Network
Training Material
Principle of Telecommunication
ZTE UNIVERSITYZTE University, DameishaYanTian District, Shenzhen,P. R. China518083Tel: (86) 755 26778800Fax: (86) 755 26778999URL: http://ensupport.zte.com.cnE-mail: [email protected]
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Publishing Date (MONTH/DATE/YEAR) : 07/20/2009
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Contents
1 Overview of Signaling Network and Voice Network ...............................................................1
1.1 Signaling Network..............................................................................................................1
1.1.1 Network Level Structure ..........................................................................................1
1.1.2 Functions of Signaling Points ..................................................................................1
1.2 Voice Network....................................................................................................................2
2 CDMA Overview .........................................................................................................................5
2.1 Development of Wireless Communication.........................................................................6
2.1.1 The First Generation Analog Cellular Mobile Communication .................................6
2.1.2 The Second Generation Digital Cellular Mobile Communication .............................6
2.1.3 The Third Generation Mobile Communication - IMT2000........................................8
2.2 Basic Concepts of CDMA ................................................................................................10
2.2.1 Multiple Accesses Technology ...............................................................................10
2.2.2 CDMA-related Concepts........................................................................................12
2.3 CDMA Features ...............................................................................................................13
3 CDMA Network Architecture ...................................................................................................17
3.1 System Architecture.........................................................................................................17
3.2 An Introduction to Network Entities..................................................................................19
3.2.1 BTS Subsystem.....................................................................................................19
3.2.2 Mobile Switching Subsystem.................................................................................19
3.2.3 Operation and Maintenance Management Subsystem (OMM)..............................21
3.3 Interfaces and Protocols ..................................................................................................22
3.3.1 Interfaces...............................................................................................................22
3.3.2 Interface Protocols.................................................................................................24
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4 Numbering Plan .......................................................................................................................29
4.1 Numbering Plan...............................................................................................................29
4.2 MDN ................................................................................................................................29
4.3 IMSI and MIN...................................................................................................................30
4.4 Equipment Number..........................................................................................................31
4.5 Temporary Local Directory Number (TLDN) ....................................................................31
4.6 Electronic Sequence Number (ESN) ...............................................................................31
5 CDMA Key Technologies.........................................................................................................33
5.1 Basic Concept .................................................................................................................33
5.1.1 Walsh Code ...........................................................................................................33
5.1.2 Pseudo-random Sequence Number ......................................................................33
5.1.3 Number Application ...............................................................................................35
5.1.4 Number-based Channels.......................................................................................35
5.2 Key Technologies ............................................................................................................36
5.2.1 Power Control Technology.....................................................................................36
5.2.2 Diversity Technology..............................................................................................38
5.2.3 Handoff Technology...............................................................................................38
5.2.4 Voice Coding Technology ......................................................................................41
5.2.5 Channel Modulation Technology............................................................................41
5.2.6 Soft Capacity .........................................................................................................43
6 Services and Functions ..........................................................................................................45
6.1 CDMA Services ...............................................................................................................45
6.1.1 Telecommunications Services ...............................................................................45
6.1.2 Supplementary Services........................................................................................45
6.1.3 WIN Service ..........................................................................................................47
6.1.4 Value-added Service .............................................................................................47
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6.2 Network Functions...........................................................................................................47
6.2.1 Network Functions for Supporting Services ..........................................................47
6.2.2 Network Functions for Supporting the Running of the Cellular System.................48
6.2.3 Additional Network Functions for Call Processing .................................................49
6.2.4 Authentication Function.........................................................................................49
6.2.5 Roaming Function between Different Modes ........................................................49
6.2.6 International Roaming ...........................................................................................49
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CDMA-3GCN_I_01_200904
Principle ofTelecommunication
After you have completed this course, you will be able to:>> Know the overview of signaling network and voice net-
work.
>> Know the CDMA overview.
>> Master CDMA network architecture.
>> Know the numbering plan.
>> Know the CDMA key technologies.
>> Know the services and functions.
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1
1 Overview of Signaling Network and Voice Network
Key Points
Signaling network
Voice network
1.1 Signaling Network
1.1.1 Network Level Structure
The SS7 signaling network adopts a three-level structure, consisting of
HSTP, LSTP. and SP. The two-level structure is also can adopted,
consisting of HSTP&LSTP and SP. The structure is shown in Figure 1.1-1.
HSTP&LSTPFirst-level HSTP
Second-level
LSTP
Third-level SP SP
Figure 1.1-1 Structure of SS7 Signaling Network
The signaling points of the CDMA network consists of MSC, VLR, HLR,
authorization center, service control point and the mobile special service
center.
1.1.2 Functions of Signaling Points
The HSTP (high-level signaling transfer point) transfers the signaling
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messages of the second-level LSTP (low-level signaling transfer point)
and the third-level SP it connects to. HSTP should adopt the stand-alone
signal transfer point (STP) devices, and provides the functions required
by MTP, SCCP, TC and OMAP.
LSTP is the second-level STP, which transfers the signaling message of
the third-level SP connected with it. An LSTP can be independently set
up, or set up together with an SP. LSTP is implemented by stand-alone
STP devices, or the integrated STP devices combined with SP. When the
stand-alone STP devices are adopted, LSTP meets all the function
requirements of HSTP. With integrated STP devices, LSTP meets all the
function requirements of the stand-alone STP, and the function
requirements of ISUP and MAP in the No .7 signaling mode.
The third-level SP is the source or destination in the signaling message
transfer of the signaling network. Based on different functions, it should
meet the function requirements of MTP, TUP, ISUP, SCCP, TC, MAP and /
or OMAP.
1.2 Voice Network
The digital mobile communication network adopts a three-level structure,
namely, TMSC1, TMSC2 and local MSC.
In a large region, TMSC1 is established, and different TMSC1s are
connected like a mesh. In a province, one or two TMSC2s are
established, and TMSC2s are connected with the associated TMSC1. The
whole network is divided into several local MSCs, and each local MSC
has one or several MSCs which are connected with associated TMSC2.
The connection is shown in Figure 1.2-1.
The mesh networks at the same level are connected, as shown in Figure
1.2-2.
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TMSC1
Local MSC
TMSC2
Figure 1.2-1 Three-Level Voice Network Structure
TMSC1
TMSC1
Figure 1.2-2 Mesh Network Connection
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2 CDMA Overview
Key points
The development history and trend of mobile communication
What is CDMA system?
CDMA features.
The objective of mobile communication is to implement communication
at any time, any place and between any people.
The wireless mobile communication technology is basically focused on
the innovative development of mobile communication bands, reasonable
and efficient use of frequency resources, as well as compact, light and
multifunctional design. Ever since 1970s when the “Cellular” theory was
sponsored by the Bell laboratory in America, cellular communication has
been widely used. Theoretically, the essence of the cellular system is to
repeatedly use wireless channels in different geographic locations, which
is frequency division multiplexing. Divide the service area into a number
of abstract hexagonal cellular cells, while two nonadjacent cells use the
same frequency. The cell size is determined according to the user
density. In this way, spectrum utilization can be greatly enhanced and
the system capacity can thus be effectively raised. Meanwhile, based on
the development of microelectronic technology, computer technology,
communication network technology, signal coding technology and digital
signal processing technology, the development of mobile communication
has gained a great leap forward on such aspects like switching, signaling
network system and wireless modulation and coding technology. Thus,
the cellular mobile communication system has experienced a series of
changes, from analog to digital, from Frequency Division Multiple Access
(FDMA) to Time Division Multiple Access (TDMA) and Code Division
Multiple Access (CDMA), and the evaluation from the first generation
cellular mobile communication system to the third generation mobile
communication system.
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2.1 Development of Wireless Communication
2.1.1 The First Generation Analog Cellular Mobile Communication
In late 1970s, the first generation cellular mobile communication system
was developed on the basis of the cellular networking technology. It
created the first case for the commercialization of cellular mobile
communication system. The first cellular system AMPS (Advanced Mobile
Phone Service) was realized in Chicago in 1979. During the same period,
other systems were also under development, including TACS in UK and
NMT in North Europe.
The first generation communication featured FDMA and analog
modulation (FM). Voice transmission was achieved through analog
signals. It was restricted by a series of factors, such as low frequency
unitization, small capacity, lack of unified international standards and
effective anti-interference / anti-attenuation measures, complicated
equipment, high cost, poor voice quality and security. Apart from this, it
required a protection band and could be intercepted easily by number
cloning. The number of subscribers was also limited. Non-voice and
digital communication services were impossible. Therefore, it could not
satisfy the requirements of market development. These fatal
disadvantages hindered its further development and it was inevitably
replaced by digital cellular mobile communication step by step.
2.1.2 The Second Generation Digital Cellular Mobile Communication
Developed in the 1990s, the mobile phone system featuring TDMA and
narrow-band CDMA is called as the second generation mobile
communication system. There are two typical product categories:
2.1.2.1 TDMA system
The major feature of TDMA series products is the adoption of TDMA and
FDMA technologies to implement mobile communication. The mature
and representative systems include Pan-European GSM, American
D-AMPS and Japanese PDC. Their common features were presented by
digitalization, TDMA, better voice quality, excellent security, data
transmission capability and the function for automatic roaming. Each of
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them had their own advantages and shortcomings: The PDC system
uses high spectrum utilization, but only available in Japan. The D-AMPS
system has the largest capacity but its equipment is very complicated.
The GSM technology maturity is based on open standards and widely
used around the world.
2.1.2.2 N-CDMA system
The CDMA wireless technology is an innovative digital cellular technology
developed after the communication technologies like GSM. The N-CDMA
series is the narrowband CDMA based on IS-95 and developed under the
sponsorship of Qualcomm.
Featuring digital transmission was based on a series of key technologies,
including spreading communication, power control, soft capacity, soft
handoff, voice activation; voice coding, multiple access, diversity
receiving and RAKE receiving. Hence the CDMA system has obtained
more advantages and has pushed the mobile communication technology
to a new development stage.
The advanced technologies have granted the CDMA system with
overwhelming advantages over the TDMA system, such as high
spectrum utilization, wide coverage, large system capacity, simple
frequency planning, high voice quality, fine anti-resistance, small
radiation power, power saving, long standby time, strong penetration
capability, excellent indoor coverage, high security and excellent
prevention against number cloning.
The development of CDMA is a progressive process. Most commodities
available on the market are developed on the basis of the IS-95A
narrowband N-CDMA technology. This system features low cost, high
quality, interconnection, supports IP and data services, implements
Wireless Intelligent Network (WIN) service and provides convenient and
efficient communication services to users. On the aspects of
communication technologies and people’s requirements, the future
wireless communication world will be a broadband-based, integrated
data and multimedia network. The broadband CDMA technology will be
an important support to this network.
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2.1.3 The Third Generation Mobile Communication - IMT2000
2.1.3.1 Development Motive of the Third Generation Cellular Mobile Communication System
Represented by AMPS and TACS, the first generation cellular mobile
communication system provided a solution to mobile conversation and
greatly satisfied the requirements of terminal users, but many problems
existed in this system. For example, poor conversation quality, low
spectrum utilization and security and so it was replaced by the second
generation cellular mobile communication system represented by GSM
and IS95. Compared to the first generation, great improvement was
achieved in terms of conversation quality, spectrum utilization, security
and confidentiality. It satisfied people’s requirements in a certain period.
Along with the continuous development of mobile communication and
the expansion of mobile communication scale, the disadvantages of the
second generation were also exposed gradually.
1. Insufficient radio frequency resources
The rapid increase of mobile terminal users made the frequency
resources of the system relatively insufficient. The development of
mobile communication surprisingly exceeded expectations. To
expand system capacity, the cell of some central cities was shrunk
less than 500 meters in diameter that resulted in frequent handoff
and serious interference and thus the conversation quality became
fairly poor.
Low frequency utilization was another key reason for frequency
resource insufficiency. Compared to the first generation mobile
communication, the second generation raised the frequency
utilization, but compared with the third generation with the CDMA
technology as the core; its frequency utilization is still very low.
2. Unable to meet the requirements for new services
The second generation features the voice-oriented design, with its
main objective focused on providing quality and efficient voice
services. Along with the development of the Internet and electronic
commerce, data service will become the main stream. In the future,
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various broadband information services such high-speed data,
low-speed image and television will become the application used
most frequently by terminal users. But the second generation was
designed mainly for voice services, which cannot provide high-speed
data service.
2.1.3.2 Third Generation Cellular Mobile Communication System
This system (3G) is also called as IMT-2000, which means that its
working band is 2000MHz and its highest service rate can go up to
2Mbit/s. Based on the broadband W-CDMA technology, it is a multimedia
and intelligent system that is able to raise multiple transmission rates,
integrate terrestrial cellular system, cordless system, cellular mobile
communication system and satellite system, and thus implement global
services in real sense. It provides a centralized platform for the
integration and allocation of various services. The 3G system has three
main features:
1. Seamless Global Roaming.
2. High-speed transmission; High-speed mobile environment: 144kbit/s;
Walking slow-speed mobile environment: 384kbit/s; Indoor still
environment: 2Mbit/s.
3. Seamless service transfer, namely, service interworking is available
among fixed network, mobile network and satellite network.
2.1.3.3 Evolution from 2G to 3G
As described above, two development directions are undergoing. Figure
2.1-1shows the evolution of the N-CDMA system based on IS-95A to the
3G system.
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IS 95-A 14.4kb p s
IS 95-B64kb p s
cd m a2000 1XP h ase I 144kb p s
cd m a2000 1X E V D O P h ase II 2M b p s
2 G 3 G
Figure 2.1-1 Evaluation from 2G to 3G
IS-95A embedded the IP protocol in the mobile station, so the network
does not require additional IP layer on the packet transmission layer. In
this way, the hardware will be compatible with all subsequent standard
networks based on the IP. The data transmission rate of the IS-95A
network is 14.4kbit/s; In the IS95-B network, the data transmission rate
is raised to 64kbit/s through core network and wireless network
upgrading. A set of data basic equipment is added to the Base Station
Controller (BSC) to promote the CDMA system into a packet mode
network. CDMA2000 1X is the first stage of CDMA2000. It has effectively
doubled the original voice capacity and raised the data transmission rate
to 144kbit/s. It may provide a typical rate of 130kbit/s for terminal
users. CDMA2000 1XEVDV is the second stage of CDMA2000. It
intended to integrate the capability of the first stage to the same carrier
and still maintain the capability of packet data service transmission at
the split carrier. In this stage, three modes of services are provided:
realtime, non-realtime and combined realtime/non-realtime. 2Mbit/s
data transmission rate can also be provided in this stage.
2.2 Basic Concepts of CDMA
2.2.1 Multiple Accesses Technology
It is known that the first concern of any transmission system is how to
establish channel connection between terminal users within the network
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and within the electric wave coverage of the wireless communication
environment. The essence of this problem is multi-access mobile
communication. Currently this mode is used by FDMA in the analog
system, TDMA and CDMA in the digital system. The theoretical basis of
multi-access connection implementation is the signal splitting technology,
namely, implementing appropriate signal design at the sending end, so
that the signals sent from individual stations are different and while the
receiving end has the identifying capability to detach and select the
corresponding signal from the combined signals.
FDMA stands for Frequency Division Multiple Access. In this case, signal
power is centralized to a relatively narrow channel in frequency domain
for transmission. Different signals are allocated to channels of different
frequency. Interference to and from adjacent channels is restricted
through bandpass filter. So, only the energy for useful signals is allowed
through the specified narrow channel, while signals of other frequencies
are excluded out.
TDMA stands for Time Division Multiple Access. One channel consists of
a series of periodic timeslots. The energy for different signals is assigned
to a different timeslot. Interference from adjacent channels can be
restricted through timed channel selection. Only the energy for useful
signals is allowed through the specified timeslot.
CDMA stands for Code Division Multiple Access. Each signal is assigned
with a pseudo-random binary code for spreading. The energy for
different signals is assigned to a different pseudo-random sequence. In
the receiver, signals are detached with a correlator. The correlator only
receives selected binary sequence and compresses its spectrum. The
bandwidth of any signals mismatching the binary sequence of this user
will be compressed. As a result, only the information of useful signals
can be identified and extracted.
Figure 2.2-1 illustrates the correspondence among FDMA, TDMA and
CDMA in frequency domain and time domain.
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FDMA TDMA CDMA
Figure 2.2-1 FDMA, TDMA and CDMA Time Domain and Frequency Domain
2.2.2 CDMA-related Concepts
CDMA is based on the frequency spreading technology, namely,
modulating the information data of certain signal bandwidth to be sent
with a high-speed pseudo-random code whose bandwidth is far greater
than the signal bandwidth, so that the bandwidth of the original data
signal can be spread and then sent out via carrier modulation. Using the
same pseudo-random code, the receiving end completes the correlated
processing, converts the broadband signal into the original narrowband
signal of the original information data (namely dispreading) and
implements information communication.
Note
The spreading technology means converting the bandwidth of the
original signal to a much wider bandwidth for transmission in order to
enhance the anti-interference feature of the communication system. The
mathematical model is based on the Shannon formula in the information
theory. In the case of white noise interference, the channel capacity is:
C = B log2(1 + S / N)
B: channel bandwidth; S: signal average power; N: noise average
power;
C: channel capacity.
The above formula shows: Even if the signal-noise ratio (S/N) is low,
increasing the bandwidth B can still ensure high quality communication
without lowering system capacity.
Time TimeFrequency
Frequency Time Frequency
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CDMA is a self-interference system. All users occupy the same
bandwidth and frequency. Its working mechanism can be illustrated with
a contract example.
Let us assume that bandwidth is analogous to a big house, and there
are a large number of people present in the house speaking different
languages. They can hear their companion’s voices but also suffer
interference from conversations of other people. In this house, the air
can be imagined as the broadband’s carrier, while the different
languages can be regarded as codes. If the number of people is steadily
increased over time, we can reach at a time when we are overwhelmed
by the background noise. If the signal strength of other users can be
controlled, more users can be accommodated and high conversation
quality can be ensured at the same time.
2.3 CDMA Features
The CDMA mobile communication network is combined through multiple
technologies such as spreading, multiple accesses, cellular networking
and frequency reuse. It is the coordination of three-dimension signals
among frequency domain, time domain and code domain. Therefore it
features excellent performance against interference and multi-path
attenuation, high confidentiality and security. The same frequency can
be reused in multiple cells. Its carrier-to-interference ratio (C/I) is
smaller than 1. Trade-off optional is available between capacity and
quality. These attributes grant the CDMA system with very important
advantages over other systems.
1. Wide coverage
In the mobile communication system field, a comparison between
CDMA and GSM systems may reveal that the coverage radius of the
former is theoretically 2 times of that of a standard GSM system. To
cover 1000 km2, only 50 BTSs are required in the CDMA system, but
200 BTSs are needed in the GSM system. Less BTSs for the same
coverage means a big decrease of equipment investment for
network operators.
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2. Large capacity
In the same spectrum utilization, the capacity of CDMA is 4-5 times
of that of GSM or 10 times of that of an analog network.
3. High voice quality
The CDMA system ensures high voice quality. The noise chip can
dynamically adjust the data transmission rate and select a different
level for transmission, according proper threshold. Meanwhile the
threshold may change according to the background noise level.
Therefore, good conversation quality can still be ensured even in the
case of high background noise. The voice quality provided by the 8K
code of CDMA’s variable noise chip is no worse than the 13K code of
GSM. The 13K code provides voice service almost as good as wired
telephone and can even do better than wired telephone on the
aspect of background noise. Meanwhile, the soft handoff technology
is integrated in the system, which means “First connect then
disconnect”, so the defect “easy call failure” of hard handoff is
completely avoided.
Note
Soft handoff is the handoff of a terminal at the same frequency but
between different channels. The channel handoff within the same
BTS between different sectors is called as softer handoff. To the
opposite, the handoff at different frequencies and between different
channels is called as hard handoff.
4. Green mobile phone
In the CDMA system, different power control technologies are used,
so the average power is decreased a lot compared to that of the
GSM system and the radiation is also lowered, which ensures that
the system can be used safely.
5. High frequency utilization
In the CDMA system, different pseudo-random codes are used for
user signal modulation. On the aspects of frequency domain, the
spectrum of all signals are overlaid, therefore the spectrum
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utilization is very high.
6. Simple frequency planning and easy expansion
Users can be identified according to different sequence codes,
therefore, different CDMA carriers can be used in adjacent cells and
the network can be flexibly planned and easily expanded.
7. Secure connectivity
8. Excellent performance against interference and multi-path
attenuation
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3 CDMA Network Architecture
Key points
The basic architecture and some functions of the CDMA network.
Descriptions of individual interfaces and the information transferred
over them.
Protocols related with the CDMA network.
3.1 System Architecture
The CDMA cellular mobile communication system consists of four
independent subsystems: Mobile Station (MS), Base Transceiver
Subsystem (BSS), Mobile Switching Subsystem (MSS) and Operation &
Maintenance Subsystem (OMM). MS and BSS can communicate directly,
while the communication between BSS and MSS is implemented through
the standard A interface. Other interfaces, such as B, C, D, E, H, M, N, O
and P represent the interfaces among the functional entities. When
different functional entities are configured in each physical unit, some
interfaces will become internal interfaces that may not follow the unified
interface standard. Ai, Di and Pi are the system’s interfaces to
interconnect with other communication networks. Figure 3.1-1shows the
architecture and interfaces of the CDMA system:
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MSCA AiBSCBTS Abis
MS
OMC HLR
C
Um
AUC H
Q Q
D VLR
B
VLR
G
SC
N
SCSMESME M M M
PSTN
PSPDN
ISDN
Pi
Di
EIR IWFMSC
F LE
Figure 3.1-1 Network Architecture of the CDMA Cellular Mobile Communications
System
BSC Base Station Controller Base station controller
BTS Base Transceiver Station Base station transceiver
MSC Mobile services Switching Center MSC
OMC Operation and Maintenance
Center
Operations & maintenance
center
AUC Authentication Center Authentication Center
EIR Equipment Identification Register Equipment Identification
Register
HLR Home Location Register HLR
VLR: Visitor Location Register VLR
MS Mobile Station Mobile station
ISDN Integrated Services Digital
Network
Integrated service digital
network
PSTN Public Switched Telephone
Network
Public Switching Telephone
Network
PSPDN Public Switched Public Data
Network
Public Switched Public Data
Network
PLMN Public Land Mobile Network Public land mobile network
SC Short Message Center Short message center
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3.2 An Introduction to Network Entities
3.2.1 BTS Subsystem
The BTS Subsystem (BSS) is the assembly of radio equipment and radio
channel control equipment, serving one or more cellular cells. In certain
radio coverage, it is controlled by the Mobile Switching Center (MSC) to
implement channel assignment, user access and paging, and
information transfer. Normally, the BSS consists of one or more BSCs
and BTSs. The BTS is responsible for radio transmission and BSC for
control and management.
3.2.1.1 Base Transceiver
The Base Transceiver (BTS) belongs to the radio part of a base station
system. Controlled by BSC, it serves the radio transceiving equipment of
a certain cell, implements the conversion between BSC and radio
channels, radio transmission through air interface between BTS and MS
and related control, and communicates with BSC through the Abis
interface.
3.2.1.2 Base Station Controller
One end of the Base Station Controller (BSC) can be connected with one
or more BTSs, while its other end can be connected with MSC and OMC.
Oriented to radio network, BSC implements radio network management,
radio resource management and radio BTS monitoring and management.
It also controls the establishment, connection and disconnection of radio
connection between MS and BTS, controls the positioning, handoff and
paging of MS, provides voice coding and rate adjustment and carries out
operation and maintenance of the BSS.
3.2.2 Mobile Switching Subsystem
The Mobile Switching Subsystem (MSS) implements the main switching
functions of the CDMA network. Meanwhile it manages the database for
user data and mobility.
3.2.2.1 Mobile Switching Center
MSC is the core of the CDMA network. It controls and implements voice
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channel connection for MSs within its coverage, namely serving as an
interface between CDMA and other networks. The functions MSC carries
out include call connection, charging, BSS-MSC handoff, assist radio
resource management and mobility management. Besides, each MSC
also implements the GMSC function for call route establishment to the
MS, namely, to query the location information of each MS.
MSC gets all data required for call request processing from three
databases, VLR, HLR and AUC.
3.2.2.2 Visitor Location Register
The Visitor Location Register (VLR) is a dynamic user database, storing
the related user data of all MSs (visitors) within the MSC’s management
range, including user ID, MS’s location area information, user status and
services available for the user.
VLR gets and stores all necessary data from the HLR of a mobile
subscriber. Once the mobile subscriber leaves the control area of the
VLR, it will be registered in another VLR, and the previous VLR will
delete its data log.
3.2.2.3 Home Location Register
The Home Location Register (HLR) is a static database, storing the data
for mobile subscriber management. Each mobile subscriber should be
registered in its HLR. It stores two kinds of information: parameters
related with the mobile subscriber, including the subscriber’s ID, access
capability, user type and supplementary service; current location
information of the subscriber for call route establishment. For example:
the address of MSC or VLR. No matter where the mobile subscriber
roams, its HLR should provide all related parameters and input the latest
location into the database.
3.2.2.4 Authentication Center
The Authentication Center (AUC), a functional entity managing the
authentication information related with mobile stations (MS). It
implements MS authentication, stores the MS authentication parameters,
generates and sends the corresponding authentication parameters
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according to the requests of MSC or VLR, including A-KEY, SSD, ESN,
MIN and AAV, and then calculates all random numbers to get the
authentication result.
3.2.2.5 Short Message Center
The Short Message Center (SC) is responsible for receiving, storing and
forwarding short messages between the CDMA mobile subscribers and
fixed line users or between mobile subscribers. It serves as a postal
office, receiving mails from every place, sorts them out and then
distribute them to the corresponding users. Through SC, the messages
can be sent to destination more reliably.
The short message services include point-to-point server and cell
broadcast service.
Note
Currently the MSC of ZTE features the functions of the Intelligent
Network (IN) Service Switching Point (SSP) to process IN service
requests at the Service Control Point (SCP).
For convenient management, MSC is always combined with VLR.
Besides, the signaling to AUC must pass HLR first, so HLR and AUC are
normally combined together to minimize network load.
3.2.3 Operation and Maintenance Management Subsystem (OMM)
The Operation & Maintenance Center (OMC) provides equipment
operators with network operation and maintenance services. The OMC
helps the operators manage subscriber information, make network
planning and improve the efficiency and service quality of the whole
system. OMC includes OMC-S and OMC-R, depending on the part for
maintenance. OMC-S is responsible for the maintenance on the MSS side
while OMC-R is responsible for the maintenance on the BSS side. Its
specific functions include: maintenance test, obstacle check and
handling, system status monitoring, realtime system control, office data
modification, performance management, subscriber tracking, alarm and
traffic measurement.
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3.3 Interfaces and Protocols
According to the Open System Interconnection (OSI) model, we can
analyze the CDMA network on the aspects of interface, protocol and
interface functions in detail.
3.3.1 Interfaces
As shown in Figure 3.1-1, various interfaces exist in the CDMA system.
They can divide into the following categories according to different
subsystems: Air interface Um between mobile terminals and the BSS; A
interface between BSS and MSS, and other interfaces between internal
entities of the network.
3.3.1.1 Air interface
The Um interface is defined as the communication interface between MS
and BTS. It is the key distinguishing factor between CDMA network and
GSM network and is also the most important interface in CDMA network.
This interface grants compatibility to MSs from different suppliers and
networks of different operators, enables MSs to roam, ensures the
frequency efficiency of the cellular system, and adopts a series of
anti-interference technologies and interference preventing measures.
Obviously, the Um interface implements the physical connection from
MS to the fixed part of the CDMA system, i.e. the wireless connection.
Besides, it transfers information for radio resource management,
mobility management and connection management.
3.3.1.2 Interface between BSS and MSS – A interface
The A interface is located between MSC and BSC. Its physical link is
implemented through standard PCM digital transmission link of
2.048Mbit/s. It transfers information for MS management, BTS
management, mobility management and connection management.
3.3.1.3 BSS internal interface (Abis)
An interface between BSC and BTS is called the Abis interface. BSC on
the Abis interface provides signaling control information for BTS
configuration, monitoring, and testing and service control. Please refer
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to related documentation about the BTS side.
3.3.1.4 MSS internal interfaces
Figure 3.3-1 Internal Interfaces of the Network
In Figure 3.3-1, the MSS part contains the names of interfaces between
equipment entities. They will be described one by one in the coming
part.
1. B interface
As an internal interface between VLR and MSC, the B interface is
used by the MSC to request the current location information of the
MS from VLR or notify the VLR to update the location information of
the MS.
2. C interface
As an interface between HLR and MSC, the C interface transfers
information for route selection and management. Once a call is
required to a MS, the Gateway MSC (GMSC) will request the roaming
number of the called MS from the HLR of the called side. The
physical link of the C interface is 2.048Mbit/s standard PCM digital
transmission cable.
3. D interface
As an interface between HLR and VLR, the D interface exchanges
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information related with MS location and user management. It
ensures that the MS can establish and receives calls within the entire
service area. Its physical link is 2.048Mbit/s standard digital link.
4. E interface
It is the interface controlling different MSCs of adjacent areas. When
the MS moves, during a call, from the control area of one MSC to
that of another MSC, this interface can be used to exchange related
handoff information to activate and complete handoff, and thus to
complete the cross-cell channel handoff process without interrupting
the communication. Its physical link is implemented through
2.048Mbit/s standard digital link between MSCs.
5. N interface
This interface is used to transfer route information related to the
called subscriber between MC and HLR. Its physical link is
implemented through 2.048Mbit/s standard digital link.
6. Q interface
It is an interface between MS and MSC transferring short messages.
Note
In the CDMA System; Um, A interface and other interfaces on the
network side are all open interfaces. The Abis interface is normally used
as an internal interface. If MSC and VLR are combined, the B interface
will be used as an internal interface. All open interfaces are compliant
with standard protocols.
3.3.2 Interface Protocols
A protocol is the common language among various functional entities. It
transfers messages through interfaces to establish an effective
information transmission channel to complete all communication and
management functions of the CDMA system. Different interfaces may
require different physical links to complete their own functions. When
the hierarchical protocol structure is adopted for the system’s interfaces,
the interworking with ISDN can be considered. Therefore, the interfaces
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match the OSI reference model. The purpose of this structure is to allow
the isolation of different signaling protocols, describing protocols
according to continuous independent hierarchy. Each layer of protocol
provides specified service at the agreed service access point for its
upper layer protocol. Figure 3.3-2 shows the protocol structure of the
CDMA network.
Figure 3.3-2 CDMA Network Protocol Structure
On the BTS side, the IS-95 protocol of Qualcomm is used for the CDMA
system.
At the A interface, related standards stipulated by the Ministry of
Information Industry. The signaling model is shown in Figure 3.3-3:
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A 口 BSC MSC
DTAP BSSMAP DTAP BSSMAP
Allocation function Allocation function
SCCP SCCP
MTP MTP
DTAP: Direct Transfer Application Part
BSSMAP: BSS Mobile Application Part
SCCP: Signaling Connection Control Part
MTP: Message Transmission Part
Figure 3.3-3 Signaling Protocol Reference Model of A Interface
The third layer consists of DTAP and BSSMAP. DTAP messages are
transparent to the A interface, therefore the A interface supports various
air interfaces to implement call processing and mobility management,
while radio resource management is mapped into a BSSMAP message
and then transferred through the A interface.
Layer 2: Based on the MTP of SS7 signaling.
Layer 1 features digital transmission at the rate of 2048 Kbit/s.
On the network side, the functional entities communicate through SS7
MAP protocol, which reflects the SS7 signal protocol structure.
M T P
S C C P
M A P
T C A P
IS U P T U P
Figure 3.3-4 SS7 Signaling Hierarchical Structure
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Note
Concepts related with the SS7 signaling system are widely used in the
CDMA network. Information transfer is implemented through the MAP
application layer among MSC, VLR, HLR, AUC and SC. Due to its
important position, SS7 will be described separately in this set of
textbooks.
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4 Numbering Plan
Key points
Understand the meanings of each number in the CDMA network
Remember the numbering rules for each number.
In the CDMA network, different numbers are used in different places.
Because of the roaming feature of mobile subscribers, these numbers
must be accepted and identified at any switching equipment. Therefore,
in mobile communication, it is necessary to give a unified numbering
plan for different numbers to enable entities in the network to
distinguish and identify mutually.
4.1 Numbering Plan
In CDMA networking, we use the following numbering plan:
1. E.164: The international public telecommunication numbering plan.
All country codes (CC) are assigned by ITU in Recommendation
E.164.
2. E.212: International identification plan for mobile terminals and
mobile users
All mobile country codes (MCC) are assigned by ITU in
Recommendation E.212.
4.2 MDN
The Mobile Directory Number (MDN) is the standard international
telephone number used to identify a given subscriber. It consists of a CC
Country Code), an MAC (Mobile Access Code ) and an SN (Subscriber
Number).
The MDN number is based on the ITU-T E.164 standard.
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Structure of the MDN:
CC: Country Code
MAC: Mobile Access Code.
SN: Subscriber Number.
In Wireless Local Loop (WLL) application, MDN can be of different
structures depending on network operators in different countries.
The standard structure for WLL will be:
MDN is sent by MSC/VLR to HLR to setup the call procedure. Usually, we
dial only the Office Code + ABCD therefore; MSC/VLR transforms the
dialed number into the above MDN format and then sent via SS7 link.
4.3 IMSI and MIN
The International Mobile Subscriber Identity (IMSI) is a unique identifier
allocated to each mobile subscriber. It consists of a MCC (Mobile Country
Code), a MNC (Mobile Network Code) and a MSIN (Mobile Station
Identification Number).
The IMSI number is based on the ITU-T E.212 standard.
This number should be written into the MS.
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MCC: Mobile country code
MNC: Mobile network code
MSIN: Mobile subscriber identification number, a 10-digit decimal
number.
MIN is defined following the AMPS standard to ensure the CDMA/AMPS
bimodal operation, and is the last 10 digits of IMSI, namely MSIN, as
required by this system.
IMSI number may vary in context depending on operators in different
countries.
4.4 Equipment Number
In CDMA networking, we use MSCIN/VLRIN/HLRIN/SCIN to identify the
networking entities and realize international routing of SS7 messages.
In CDMA networking, MSCIN/VLRIN/HLRIN/SCIN is based on the ITU-T
E.212 standard.
4.5 Temporary Local Directory Number (TLDN)
To call a mobile subscriber, VLR allocates a temporary number to the
mobile subscriber for the network to select a route.
4.6 Electronic Sequence Number (ESN)
ESN is the unique number used to identify a MS. One unique SN (Serial
Number) is allocated to every individual bimodal MS. It consists of 32
bits, and the equipment serial number is set by the MS manufacturer.
Note
The GT number is the address information of the SCCP layer. It will be
described in the description of SS7 signaling.
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5 CDMA Key Technologies
Key points
Application of codes in the CDMA system
Key technologies on CDMA.
5.1 Basic Concept
CDMA stands for code division multiple accesses. Various code
sequences may be involved in this technology. Different coding
processes are required for different sources and channels. The following
description is focused on several different codes.
5.1.1 Walsh Code
The Walsh code is originated from the Walsh function through
complicated resolution process. The process is not described in this
textbook. The point is on the attributes of Walsh code.
The Walsh function is a non-sine complete orthogonal function system.
Its possible value could be selected from +1 and –1 (or 0 and 1). It is
suitable to be used to denote and handle digital signals. Thanks to its
excellent correlation, the Walsh function can be used as address code in
CDMA communication. In IS-95, the 64-order Walsh code is used for
channel discrimination. In the CDMA system, each forward code channel
is spread with 1.2288Mbit/s 64-order function to make all forward code
channels mutually orthogonal. The code channels spread with 64-order
Walsh function n (n=0—63) can be defined as Code channel No.n.
5.1.2 Pseudo-random Sequence Number
In the communication theory, white noise is a random process. Its
transient value is subject to normal distribution. Its power spectrum is
even in a very wide range. The pseudo noise (PN) sequence, similar with
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the white noise sequence, appears random but it is actually a regular
periodic binary sequence. In the CDMA communication technology, the
address code is selected from a pseudo random sequence. From all
pseudo sequences, the m sequence is selected as the address code. Its
various phases can be used to discriminate different subscribers. This
method is used in the current CDMA cellular system.
IS-95 also uses the self correlation of the PN code, while the m
sequence has the best self correlation, therefore the PN code of the m
sequence is selected as the address code. The near orthogonal
attributes of m sequences in different phases are used to allocate a
phase for the channel of each subscriber.
The periodic donation of the m sequence is:
P = 2 n – 1 (n is the length of the shift register).
In the CDMA system, the long code and short code of the m sequence
are used: long code n=42, short code n=15.
Note
Orthogonal: a mathematics concept. If the integral of two functions
product comes to zero in a period, it can be called as orthogonal.
Correlation: can be divided as self correlation and mutual correlation.
The former is the comparison of the same signal at different time
segments, reflecting the change of wave form and the phase. Mutual
correlation refers to the relationship between two signals and is used to
indicate the difference of wave form and the phase between two signals.
The self correlation of the m sequence pseudo-random code is
approximately 1, while that of mutual correlation is approximately 0.
This is the optimal code type.
The “m” in the m sequence should not be used in its upper case. In the
pseudo sequences, the M sequence is another spreading communication
sequence.
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5.1.3 Number Application
5.1.3.1 Walsh code —— identifying forward channel
In the CDMA system, each forward code channel is spread with
1.2288Mbit/s 64-order function to make all forward code channels
mutually orthogonal.
5.1.3.2 PN 215 short number —— identifying BTS, 242 long number —— reversely identifying MS: forward identifying scrambler
Among forward channels, the m sequence of a length of 242 –1 is used to
harass the codes on the service channel. The m sequence of a length of
215 –1 is used for orthogonal modulation of the forward channel.
Different m sequences are used by different BTSs for modulation. Their
phase deviation is 64 bits at least. So, totally 512 different phases can
be available at most.
Among reverse channels, the m sequence of a length of 242 –1 is used
for spreading directly. Along with the mask value change, the phase of
the m sequence also changes. Every subscriber will be allocated with a
mask calculated through the MS Electronic Serial No. (ESN). Namely,
every subscriber will be randomly allocated with a phase of PN code
(with the length as 242 –1) and this phase is not repeated. Because of
the dual correlation attributes of the m sequence, any two subscribers
are approximately orthogonal. The PN code of 215 –1 is also used for
orthogonal modulation of reverse service channels. But it is unnecessary
to identify the BTS at the reverse channel, m sequences of the same
phase are used for all BTSs, so the phase deviation is 0.
5.1.4 Number-based Channels
5.1.4.1 Forward channel
1. Pilot channel: A channel continuously transmitting signals at
the forward CDMA channel. It is used for synchronization and
handoff of all working MSs within the coverage of the BTS.
2. Intra-frequency channel: This channel is for convolution
coding, code symbol repetition, interleaving, spreading and
modulation. In the coverage of the BTS, the active MS can get
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initial clock synchronization through this channel.
3. Paging channel: This channel is for convolution coding, code
symbol repetition, interleaving, scrambling, spreading and
modulated spreading signals. The BTS sends system information
and MS paging messages through this channel.
4. Service channel: Transfer subscriber service data. The relationship
between channels and Walsh code is illustrated in Figure 5.1-1:
Figure 5.1-1 Relationship between Channels and Walsh Code
5.1.4.2 Reverse channel
1. Access channel: The channel used by the MS to originate
communication with the BTS and by the responding BTS to send
paging channel messages. The access channel transmits a coded,
interleaved and modulated spreading signal. It is discriminated
exclusively through the public long number mask.
2. Reverse service channel: used to transmit subscriber information
and signaling information during call connection.
5.2 Key Technologies
5.2.1 Power Control Technology
This is the core technology of the CDMA system. If all subscribers in the
cell transmit signals at the same power, the signals transmitted from a
near MS to the BTS are stronger, and the signals transmitted from a far
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MS to the BTS are weaker. As a result, strong signals override weak
ones. This is called “Near/Far Effect” in the mobile communication. The
CDMA system is a self-interfering system. All mobile subscribers share
the same bandwidth and frequency. The “Near/Far Effect” is very
obvious. The purpose of CDMA power control is to wipe out this effect to
ensure that the system can provide high communication quality without
generating interference to other subscribers.
Power control includes forward power control and reverse power control,
while reverse power control can also be divided into open loop power
control only involved with MSs and closed loop power control involved
with MSs and BTS.
5.2.1.1 Reverse Open Loop Power Control
In this power control mode, the MS adjusts its transmitting power
according to its receiving power in the cell, so that the signals
transmitted by all MSs have the equal power when reaching the BTS.
This main purpose is to implement such effects as shadow compensation;
therefore, it features a large dynamic scope, at least in the range of
–32dB ~ +32dB according to the IS-95 standard.
Open loop power control is based on a rough estimation of the sending
level of a MS, while the MS estimates the sending level by measuring
the receiving power, without modulation via any forward link.
5.2.1.2 Reverse Closed Loop Power Control
The design purpose of closed loop power control is to enable the BTS to
correct the open loop power of the MS rapidly so that the MS can
maintain the optimal transmitting power. During closed loop power
control at a reverse service channel, the MS will refer to the received
effective power control bit at the forward service channel to adjust its
average output power.
5.2.1.3 Reverse Power Control
During forward power control, the BTS adjusts the transmitting power of
each MS according to measurement results. Its purpose is to allocate
light forward link power for MSs with low path attenuation and allocate
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heavy forward link power for those MSs with high BER and far from the
BTS.
The BTS decides whether to increase or decrease the transmitting power
according to the forward FER report from the MS.
5.2.2 Diversity Technology
This technology enables the system to receive two or more input signals
at the same time and the attenuation statuses of these input signals are
not related to each other. The system demodulates these signals
respectively and then adds them together. In this way, more useful
signals can be received to overcome attenuation.
The mobile communication channel is a multi-path attenuation channel.
Its attenuation can be divided into fast attenuation and slow
attenuation.
The diversity technology is an effective method to overcome multi-path
attenuation. It enables the receiver to combine several received signals
carrying the same information but of independent attenuation attributes,
before making a decision. Attenuation is related with frequency, time
and space, therefore the diversity technology involves space diversity,
time diversity and frequency diversity.
5.2.2.1 Time diversity (RAKE receiving technology)
The mobile communication channel is a multi-path attenuation channel.
The RAKE receiving technology is to receive a line of signals for
demodulation separately and then, overlay them for output to achieve
enhanced receiving effects. The multi-path signal is not a negative factor,
but can be a favorable factor in the CDMA system.
5.2.2.2 Frequency diversity
The CDMA bandwidth transmission is the specific application of
frequency diversity.
5.2.3 Handoff Technology
The following types of handoff may be involved when the MS
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implements communication via the service channel:
5.2.3.1 Soft handoff
Soft handoff happens between CDMA channels of the same frequency
but in adjacent cells. In this type of handoff, when the MS starts to
communicate with a new BTS, the communication with the original BTS
is not immediately cut off. Soft handoff is only available for CDMA
channels of the same frequency. It can provide path diversity at the BTS
border for forward service channels and reverse service channels. Figure
5.2-1 shows a soft handoff between different BTSs within the same BSC;
while Figure 5.2-2 shows a soft handoff between different BSCs within
the same MSC.
Figure 5.2-1 Soft handoff Within the Same BSC
Figure 5.2-2 Soft handoff between Different BSCs within the Same MSC
5.2.3.2 Softer handoff
The handoff between CDMA channels in different sectors but with the same
frequency and within the same BTS is called as softer handoff. Figure 5.2-3
reflects the softer handoff process.
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Figure 5.2-3 Softer Handoff Process
5.2.3.3 Hard handoff
In this handoff mode, the MS will first get disconnected from the original BTS
and connected with a new BTS. The handoff normally happens at CDMA channels
of different frequencies or between different MSCs, as shown in Figure 5.2-4.
Figure 5.2-4 Hard Handoff
5.2.3.4 Handoff from CDMA to analog
In this handoff, the MS transfers from a CDMA service channel to an
analog voice channel.
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5.2.4 Voice Coding Technology
At present, the voice coding of the CDMA system falls in two types:
Code-Excited Linear Prediction (CELP), 8 kbps and 13 kbps. The voice
quality of 8kbps voice coding is as good as the 13kbps voice of GSM, or
even better. The voice quality of 13 kbps voice coding is as good as that
of the fixed toll call. The CELP is based on the same principles as the
PELPC, just different in that the pulse position and amplitude are
replaced by a vector code table.
5.2.5 Channel Modulation Technology
Reverse CDMA channels include access channels and reverse service
channels. These channels are used at the same CDMA frequency
through direct sequence spreading CDMA technology. Data transmission
is implemented in the unit of frame 20ms. Any data, before transmission,
will be processed in a series of links: convolution coding, block
interleaving, 64-order orthogonal modulation, direct sequence spreading
and baseband filtering.
Forward CDMA channels include pilot channel, intra-frequency channel,
paging channel (7 at most) and a number of service channels. Each
code channel will be orthogonally spread through a Walsh function and
then spread through a 1.2288Mchip/s PN sequence.
The following part describes the digital spectrum spreading mechanism
and the changes of signal spectrum after spreading, as shown in Figure
5.2-5 and Figure 5.2-6.
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Cell coding
Walsh code
Channelcoding
(spreading)Carrier
modulationCarrier
demodulationChanneldecoding
(dispreading)
Cell decoding
Cell decoding
PN pseudo-random code
Channeldecoding
(dispreading)Carrier
demodulationCarrier
modulationChannelcoding
(spreading)
Cell coding
Walsh codeForwardreceiving
Forwardtransmission
Backwardtransmission
Backwardreceiving PN pseudo-
random code
Figure 5.2-5 Digital Spectrum Spreading
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Signal Pulse noise White noise
Signal spectrum after despreadSignal spectrum before despread
S(f)
f0
Signal
Noise
S(f)
Signal
Noise
White noise White noise
f0
S(f)
Signal spectrum before spread
Signal
S(f)
f0
Signal spectrum after spread
Signal
f0 f0
Figure 5.2-6 Signal and Noise Spectrum Change
5.2.6 Soft Capacity
In the CDMA network, two methods are available for dynamic capacity
adjustment:
1. Raise FER to get more available channels by lowering voice quality.
2. Cell breath function: Adjust the pilot value of the BTS to adjust the
cell’s coverage.
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6 Services and Functions
Key points
An introduction to the main services of the CDMA network
Major functions
6.1 CDMA Services
6.1.1 Telecommunications Services
The CDMA network can offer the following telecommunications services
to the subscribers:
1. Voice service
The voice codec adopts EVRC. 8K QCELP should be supported in the
area where the GreatWall Network is deployed to support the
subscribers of the existing subscribers of the GreatWall Network.
2. SMS service
The following SMS services should be supported:
· MS-originated SMS
· MS-terminated SMS
· Cell broadcast SMS (IS824)
· Chinese (GB13000) SMS
6.1.2 Supplementary Services
6.1.2.1 Types of Supplementary Services
The following supplementary services can be offered to the subscribers.
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Table 6.1-1 Types of Supplementary Services
Service Name Remarks
Call Forward Busy (CFB)
Call Forward Default (CFD)
Call Forward No Answer (CFNA)
Call Forward Unconditional (CFU)
Call Transfer (CT)
Call Waiting (CW)
Calling Number Identification Presentation
(CNIP)
Calling Number Identification Restriction (CNIR)
Conference Call (CC)
Message Waiting Notice (MWN) It is used in the voice
mailbox service.
3-Way Calling (3WC)
Voice Message Retrieval (VMS) It is used in the voice
mailbox service.
6.1.2.2 Operations of Supplementary Services
1. Operation definition
Seven service operations are defined in the CDMA system.
1) Provision: An operation implemented by the service provider to
make the service available to the subscriber.
2) Cancellation: Reverse operation of provision. It is the operation
implemented by the service provider to make the service
unavailable to the subscriber.
3) Registration: An operation implemented by the service provider or
subscriber to make the service executable. Registration involves
the input of necessary information.
4) Erasure: An operation implemented by the service provider or
subscriber to delete the information entered for registration.
5) Activation: It is used to make the subscriber enter the "Ready to
provide service" status.
6) Deactivation: Reverse operation of activation.
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7) Request: Service execution process.
2. Subscriber operation
Among the above operations, provision and cancellation are
generally implemented by the operator; the registration, erasure,
activation, deactivation, and request operations can be performed
by the subscriber through the MS.
6.1.3 WIN Service
The WIN provides basic IN service platform in the CDMA system by
using the IN mode. The following WIN services need be implemented:
· Pre-Paid Charging
· VPN
· Freephone
6.1.4 Value-added Service
The voice mailbox provided by the CDMA network should provide
services such as message leaving, message operations, auto answer,
timed delivery, message notification, and bulletin board.
The SMS service platform provided by the CDMA network should provide
the subscribers with application-oriented wireless service data, for
example, weather forecast and stock market information.
The CDMA network should provide other value-added services as
required.
6.2 Network Functions
6.2.1 Network Functions for Supporting Services
Supporting the call processing for establishing communication with
networks such as PSTN and PLMN after the roaming.
Authenticating registration and call setup.
Supporting the telecommunications services and supplementary services
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described in Section 5.1.
Taking measures to protect the important signaling units exchanged
between the MS and the BS to avoid any unauthorized users from
getting them.
Supporting WIN and providing WIN-related services as required.
Supporting voice mailbox and SMS service and providing other
value-added services as required.
6.2.2 Network Functions for Supporting the Running of the Cellular System
6.2.2.1 Roaming
Roaming means that the MS leaves its home mobile service local
network. The MS judges whether it is roaming according to the SID, and
can prompt the subscriber of the roaming status.
To enable the network to keep track of the location of the MS, the MS
should implement location registration. The registration modes include
power-up registration, power-down registration, periodical registration,
distance-based registration, zone-based registration, parameter-change
registration, implicit registration, ordered registration, and so on.
6.2.2.2 Handoff
Handoff refers to the process of transferring the ongoing call from a cell
to another cell. Handoff is used for radio propagation, service
distribution, activation operation maintenance and clearing device fault.
There are two handoff modes in the CDMA system: soft handoff and
hardware handoff.
1. Soft handoff
With the soft handoff, the MS uses the same frequency to connect
with the new cell before disconnecting itself from the old cell.
The soft handoff falls into the four types:
· Handoff between two sectors in the same BS
· Handoff between two cells in different BSs
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· Three-party handoff between the cells/sectors in different BSs
· Handoff between different BSCs (optional)
2. Hard handoff
During the hard handoff, the traffic channel is interrupted
instantaneously.
Hard handoff falls into two types:
· Handoff between different channels in the same MSC
· Handoff between different MSCs
6.2.3 Additional Network Functions for Call Processing
The function of encrypting user voice channel should be provided. The
implementation of this function does not affect the purchase of the
devices, deployment/running of the system and whole network, or other
functions.
In the MS->network direction, after the voice channel is set up, the
system should support the sending of the DTMF signals of the users
(converting the DTMF signals to the signaling messages for transfer over
the radio interface).
6.2.4 Authentication Function
Both the MS and the system should support the authentication function.
The CAVE algorithm is used as the authentication algorithm.
Both the MS and the system should support THE SSD updating. The
system should support the sharing and non-sharing of SSD.
6.2.5 Roaming Function between Different Modes
The MS in the CDMA system can work in two modes: CDMA mode and
AMPS mode. The dual-mode MS can automatically roam between the
coverage area of the CDMA network and that of the AMPS network.
6.2.6 International Roaming
The system should support the international roaming service. To support
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international roaming, the system should support at least the following
functions:
· Analyzing the IMSI/MIN to check whether the subscriber is an
international roaming subscriber, and implementing the
corresponding processing.
· Sending international TLDN (including CC).
· Conducting conversion between China SS7, ITU SS7, and ANSI SS7
at the international gateway office.
· The charging system provides proper the charging format conversion
functions.
· Determining whether to implement authentication and whether to
share SSD according to the subscribers in different countries.
The MS can support the international roaming service. To support
international roaming, the MS should support at least the following
functions:
· Proper voice codec; EVRC is required in China.
· Adopting the numbering plan that follows the MIN-based IMSI
principles.
· Supporting proper frequency configuration.