tn_bt001_e1_0 cs principle overview-33.doc

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CS Principle Overview

Course Objectives:· Understand the development of the mobile communication

· Understand the evolution from 2G to 3G

· Understand the system architecture of WCDMA R4



Contents

1 Development of Mobile Communication....................................................................................................1

1.1 1G.............................................................................................................................................................3

1.2 2G.............................................................................................................................................................4

1.2.1 TDMA.......................................................................................................................................4

1.2.2 N-CDMA..................................................................................................................................6

1.3 3G.............................................................................................................................................................7

1.3.1 3G Technologies.......................................................................................................................9

1.3.2 Spectrum Allocation of IMT-2000.........................................................................................11

2 Structure and Evolution of the CN....................................................................................................... ....13

2.1 Network Structure in Different Phases..................................................................................................13

2.1.1 Network Structure of R99......................................................................................................14

2.1.2 Network Structure of R4........................................................................................................20

2.1.3 Network Structure of R5........................................................................................................25

2.2 Evolution Characteristics.......................................................................................................................28

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1 Development of Mobile Communication

Mobile communication refers to the communication between mobile objects or

between mobile objects and fixed object. The mobile objects include the objects in the

mobile state, including people, car, train, steamboat, airplane, and so on.

Compared with the communication between fixed objects, the mobile communication

has the following features:

1. Mobility

The communication of the mobile object is required to be kept, so the wireless

communication or the combination of the wireless and wired communication is

required.

2. Complicated electric wave propagation conditions

The mobile object may move in various environments, so the propagation of the

electric wave might result in reflection, diffraction, Doppler effect, and so on,

which may in turn result in effects such as multi-path interference, signal

propagation delay and spread.

3. Serious noise and interference

Engine ignition noise and industrial noise in city environment, inter-modulation

interference between mobile subscribers, adjacent channel interference,

cofrequency interference, and so on.

4. Complex system and network structures

The mobile communication system is a multi-subscriber communication system

and network, so it must avoid mutual interference between mobile subscribers.

Besides, the mobile communication system should also connect with the local

network, satellite communication network, data network, and so on. Therefore,

the network structure is very complex.

5. Requiring high band utilization rate and good equipment performance

There are many types of mobile communication. According to the application



requirement and situation, the mobile communication falls into four types:

1) Trunk mobile communication, also known as macro cell mobile communication.

In the trunk mobile communication system, there is only one base station; the

height of the antenna varies from dozens of meters to one hundred meters, and

its coverage radius is 30-50 km; the power of the transmitter can be up to 200W.

The subscriber capacity varies from dozens of subscribers to several hundred

subscribers. The MSs can be vehicle mounted stations and handsets; the MS can

communicate with the base station or communicate with other MSs and local

call subscribers through the base station. The base station is connected with thelocal call wired network.

2) Cellular mobile communication, also known as micro cell mobile

communication.

In the cellular mobile communication system, a large serving area is divided into

several cells; one base station is set in each cell for the connecting and

controlling the MSs in this cell; the base stations are associated with each other

through the mobile switching center, and they are connected with the local

exchange. The ultra-short wave propagation is used, so the frequency can be

reused in the cells with a certain distance in between, thus making a full use of

the frequency resources. Each cell serves over 1,000 subscribers, and the whole

coverage area can serve up to 1 million subscribers.

3) Satellite mobile communication

The mobile communication can also be implemented by transferring signals

through the satellite. The vehicle mounted stations can implement mobile

communication through the geostationary satellite; the handsets can implement

mobile communication through multiple low-earth-orbit constellation satellites.

4) Cordless telephone

For the communication of the handset that moves slowly indoor or outdoor, the

portable cordless with low power and short communication distance is used. The

cordless telephone user can implement one-way or two-way communication

with the local subscribers through the communication point.

The mobile communication system emerged in 1940s. It has experienced three

stages according to the development process and trend. The following describes



Chapter 2 Structure and Evolution of the CN

the three stages.

1.1 1G

The 1G mobile communication system adopts the cellular networking technology. The

concept and theory of cellular system was presented by units such as Bell Lab in

1960s. However, the complex control system, especially the MS control did not

provide technical basis for the cellular mobile communication until the maturing of the

semi-conductor technology, the development of large scale integrated circuit

components and the micro processor technology, and the wide application of SMT in

1970s.

The first cellular system in America, AMPS (Advanced Mobile Phone System), in

1979 when the pilot network was deployed in Chicago.

The representative 1G systems include:

1. AMPS (USA)

The AMPS uses the 800 MHz band for analog cellular transmission. It is used in

America and some Pacific Rim countries.

2. NMT-450/900 (North Europe)

NMT (Nordic Mobile Telephone) is deployed in Sweden.

3. TACS (UK)

TACS (Total Access Communication System) is the analog communication

system used in Europe and China in 1980s. It uses the band of 900 MHz.

The 1G communication system is an analog system based on the FDMA technology. Its

operating band is around 450 MHz and 900 MHz, and the frequency separation islower than 30 kHz.

The emergence of the cellular mobile communication is a revolution in the mobile

communication. Its frequency multiplexing greatly increases the system capacity; the

network intelligence enables the cell-crossing transit and roaming function and

increases the service scope.

However, the analog communication system has the following disadvantages:

1. There is no common interface between the systems;

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TN_BT001_E1_0 CS Principle Overview

2. It cannot quickly evolve to the digital system together with the fixed network,

and it is hard to the provision the digital bearer service;

3. Low frequency utilization rate, so it cannot meet the requirement for large

capacity;

4. Low security; the call can be easily eavesdropped, and the account can be easily

embezzled.

These disadvantages obstruct the further development of the analog cellular mobile

communication system. Therefore, it will be gradually replaced by the digital cellular

mobile communication system. However, the networking technologies used in the

analog system will still be used in the digital system.

1.2 2G

Because of the disadvantages of analog systems like TACS, the mobile telephone

system that was based on digital transmission, time division multiple access (TDMA),

and narrowband code division multiple access (N-CDMA) was developed in 1990s.

This system is called the second generation mobile telephone system (2G). 2G is a

digital communication system that transfers voice and data. The typical 2G systems

include GSM, DAMPS, IS-95 CDMA, and JDC (Japan).

In addition to voice communication service, the 2G can also provide low-speed data

service and short message service.

1.2.1 TDMA

The most mature and representative TDMA systems include GSM (Fan-Europe), D-

AMPS (USA), and JDC (Japan).

1. The EIA released the technical standard of the D-AMPS. In 1993, the EIA was

formally put into commercial operation in 1993. It was based on the AMPS. It

supports both digital services and analog services. Its base station and MS are

relatively complex.

The D-AMPS is also known as TDMA/IS-136. It is the digital version of the

AMPS. The D-AMPS uses the TDMA technology. Each AMPS channel can be

divided into three D-AMPS channels. As with the AMPS, the D-AMPS operates

at 800 MHz~900 MHz. The D-AMPS is used in North America.

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2. The technical standard of JDC (currently renamed PDC) was released in 1990.

The JDC was put into use in 1993. It is used in Japan only.

JDC (Japan Digital Cellular System) is a digital cellular mobile communication

system presented by China in 1989. Its standards include RCR-STD-27A and

RCR-STD-27B. It has two operating bands: 800/900 MHz and 1.5GHz. Its

technology is similar to that of the D-AMPS. It is used in Japan only.

3. The CEPT SMG released phase I standard of the GSM in 1988. Its operating

band was about 900MH. It was put into commercial use in 1990. Also in 1990,

the specification for the GSM operating at 1800 MHz is released at the request

of UK.

The GSM series include GSM900, DCS1800, and PCS1900. Their major

difference lies in the operating band. They have the following features:

1) High spectrum efficiency

The highly efficient modulator and technologies such as channel coding,

interleaving, balancing, and voice coding bring a high spectrum efficiency to the

system.

2) High capacity

Because the transmission bandwidth of each channel increases (the transmission

bandwidth of the GSM bandwidth is 200 kHz, and that in the analog system is

about 25 kHz), the carrier-to-interference ratio of the cofrequency multiplexing

is reduced to 9dB. Therefore, the cofrequency multiplexing mode of the GSM

system can be 4/12 or 3/9, or even lower (7/21 for the analog system). Besides,

the introduction of the half-rate voice coding technology and the traffic

allocation make the capacity efficiency (the number of channels of each cell in 1

MHz) 3-5 times the TACS.

3) High voice quality

In the GSM, one the transmission quality is higher than the threshold, the voice

quality is of the same level and independent of the transmission quality.

4) High security

The security is ensured through authentication, encryption, and TMSI.

5) Interconnection with ISDN, PSTN, and so on

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6) Roaming based on the SIM card

The common features of the above three products is digitization, CDMA, andhigher voice quality than 1G, high secrecy, supporting data transfer and auto

roaming, and so on.

The three systems have different advantages:

1) The PDC has a high spectrum utilization rate;

2) The D-AMPS has a high system capacity;

3) The GSM is the most mature technology; it is based on OSI, so its technical

standard is open and it has the largest development scale.

1.2.2 N-CDMA

The N-CDMA mainly involves the IS-95 based N-CDMA researched by Qualcomm.

The specification for North America digital cellular system was released by the TIA.

The TIA began to research the system, and the system was accepted by the EIA in

1990.

The IS 95 CDMA is another digital cellular standard in North America. It operates at

800 MHz and 1900 MHz. It adopts the N-CDMA technology. It is used in North

America and South Korea. The N-CDMA matures after the GSM does, so its

application is narrower than the application of the GSM. However, compared with the

FDMA and TDMA, the CDMA has many unique advantages, which make the CDMA

become the core technology of the 3G mobile communication system.

To sum up, the CDMA has the following advantages:

1. High system capacity

Theoretically, the system capacity of the CDMA digital mobile communicationnetwork is 20 times larger that of the analog network. Actually, the system

capacity of the CDMA network is 10 times larger than that of the analog

network and 4-5 times larger than that of the GSM.

2. Improved system communication quality

The soft handover technology can overcome the disadvantage of easy call drop

of the hard handover. The CDMA system operates at the same frequency and

bandwidth, so it can easily implement the soft handover technology compared

with the TDMA system, thus improving the communication quality. The CDMA

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system adopts the adaptive threshold technology to determine the rate of the

vocoder, the powerful soft handover technology with bit error correction, and

the multipath diversity receiver. Therefore, the CDMA system can provide a far

high communication quality compared with the TDMA system.

3. Flexible frequency planning

The subscribers are distinguished by different serial numbers. Different CDMA

carriers can be used within adjacent cells. Therefore, the frequency of the

CDMA network can be flexibly planned and easily expanded.

4. Suitable for multicast communication system

The CDMA system can easily use multiple CDMA channel modes and multiple

CDMA frame modes to transfer multimedia service information with different

rates. Compared with the TDMA and TDMA, the processing mode and synthesis

mode are more flexible and simple, facilitating the application of the multimedia

communication system.

The 2G mobile communication system is a digital system, but it has some

disadvantages:

1. The band is too narrow, so it cannot provide broadband information services

such as high-speed data, low-speed image, and TV image.

2. Though the GSM is known as "GoTone", it does not really support global

roaming; especially, the GSM is not widely used in USA and Japan with a large

number of mobile phone subscribers.

With the development of sciences&technologies and communication services, the

integrated service system that provides the functions of the current mobile telephone

system and diversified services is required.

1.3 3G

With the growth of the subscriber base and the development of the digital

communication, the 2G mobile telephone system gradually shows its disadvantages.

On one hand, the band is too narrow, so it cannot provide broadband information

services such as high-speed data, low-speed image, and TV image. On the other hand,

though the GSM is known as "GoTone", it does not really support global roaming;

especially, the GSM is not widely used in USA and Japan with a large number of

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mobile phone subscribers. However, with the development of sciences&technologies

and communication services, the integrated service system that provides the functions

of the current mobile telephone system and diversified services is required. Therefore,

the ITU requires the commercial 3G mobile communication system to be implemented

in 2000, namely, IMT-2000.

The ITU also calls the 3G mobile communication IMT-2000 (International Mobile

Telecommunications in the year 2000), and the telecom magnates in Europe call it

UMTS. The 3G integrates voice communication and multimedia communication. It can

provide value added services such as image, music, Webpage browsing, video

conference, and some other information services. The 3G means globally suitable

standard, new services, wider coverage, more spectrum resources, so it can support

more subscribers.

The 3G system is radically different from the current 2G system. The 3G system adopts

the CDMA and packet switching technologies, while the 2G system adopts TDMA and

circuit switching technologies. In the circuit-switching transmission mode, the line is

connected and the bandwidth is occupied whether the call parties are in conversion or

not. Compared with the 2G system, the 3G system will support more subscribers at a

higher transmission rate.

The radio transmission technology (RTT) of the 3G system has the following

requirements:

1. The variable bit rate can be offered according to the bandwidth requirement;

144 kbps (moving at high speed)

384 kbps (walking)

2 Mbps (moving in door)

2. One connection can support services with different QoS requirements at the

same time;

3. The delay requirements of different services can be met (including real-time

voice service, best-effort data service, and so on).

The key features of the 3G are as follows:

1. Including multiple systems;

2. High design consistency around the world;

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3. The services in IMT-2000 are compatible with the fixed network;

4. High quality;

5. Small portable terminals are used around the world.

1.3.1 3G Technologies

The 3G mobile communication system was released by the ITU in 1985 and was called

FPLMTS (Future Public Land Mobile Telecommunication System) at that time. After

that, since the ITU predicated that the system would be put into commercial user in

2002 and the main band of phase I of the system was around 2GHz, so the ITU

formally named the system IMT-2000. The IMT-2000 system includes terrestrial

system and satellite system.

In 1992, the WRC-92 allocated the bandwidth of 230 MHz for the IMT-2000. In March

1997, the candidate RTT schemes were solicited around the world, indicating that

beginning of the standardization phase, and the submission was due to June 1998. The

ITU-R received 16 candidate RTT schemes, including 10 terrestrial RTT schemes and 6

satellite RTT schemes. Table 1.3 -1 shows the 10 terrestrial RTT schemes.

Table 1.3-1 Terrestrial RTT Scheme

No. Submitted Technology Duplex ModeApplication

EnvironmentSubmitted by

1 J: W-CDMA FDD, TDD All environments Japan: ARIB

2 ETSI-UTRA-UMTS FDD, TDD All environments Europe: ETSI

3 WIMS W-CDMA FDD All environments USA: TIA

4 WCDMA/NA FDD All environments USA: T1P1

5 Global CDMA II FDD All environments South Korea: TTA

6 TD-SCDMA TDD All environments China: CATT

7 cdma2000 FDD, TDD All environments USA: TIA

8 Global CDMA I FDD All environments South Korea: TTA

9 UWC-136 FDD All environments USA: TIA

10 EP-DECT TDDIndoor, outdoor to

indoor

Europe: ETSI

DECT

In September 1998, the technical performance evaluation on the candidate RTT

schemes was completed. In May 2000, the IMT-2000 radio interface technical

specification (IMT. RSPC M.1457) was passed at the ITU-R 2000 yearly meeting. This

standard covers five technologies in two classes: CDMA and TDMA. Among them, the

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three CDMA technologies are mainstream technologies nowadays, including two

frequency division duplex (FDD) technologies and one time division duplex (TDD)

technology: IMT-2000 CDMA DS (WCDMA), IMT-2000 CDMA MC (cdma2000),

and IMT-2000 CDMA TD (TDSCDMA and UTRA TDD). The TDMA-based IMT-SC

(UWC136) and IMT-FT (DECT) are not so welcomed; they were supplementary

standards.

1. Technical features of CDMA2000

The IMT-2000 CDMA MC, also known as cdma2000, was presented by North

America. Its core network (CN) is IS-95 CDMA CN (ANSI-41); it is compatible

with IS-95 CDMA. The cdma2000 technology is supported by the IS-95 CDMAoperators. It is primarily used in North America and Asia Pacific. Its single-

carrier cdma2000 1X uses the same bandwidth as that of the IS-95, but its

capacity is twice that of the IS-95. The cdma2000 supports a service transfer rate

of 144 kb/s in phase I and supports 614kb/s in phase II. The 3GPP2 has

standardized this part. However, the three-carrier cdma2000 3X is complex, and

its standardization and commercial prospect are not clear yet. Currently, the

enhanced single-carrier cdma2000 1X EV draws much attention, and its

standardization is underway. It has a high commercial potential. The cdma2000

1X EV involves two phases: Data Only (DO) and Data and Voice (DV). In early

2001, cdma2000 1X was commercially deployed in South Korea and USA

successfully. Several operators in North America and Japan have announced

their choice of 1XEV-DO.

2. Technical features of WCDMA

The IMT-2000 CDMA DS, also known as WCDMA, was presented by Europe

and Japan. NTT DoCoMo, the largest mobile phone operator in Japan, presented

the coherent multi-rate wideband CDMA (W-CDMA). The 2G mobile telephone

system of Japan have not become the international standard, so Japan stuck to

international cooperation in the IMT-2000 technical scheme.

The CN of the WCDMA is based on the evolutionary GSM/GPRS network

technology, and its air interface adopts Direct Sequence/Spread Wideband Code

Division Multiple Access (DS WCDMA). Currently, this mode is widely

supported by the GSM operators in Europe, North America, and Asia Pacific and

most of the operators in Japan and South Korea, so it one of the most

competitive 3G mobile communication technologies.

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The WCDMA is a DS-CDMA technology. Its information is extended to 3.84

Mchips and it is transferred within a bandwidth of 5 MHz. It adopts multiple

technologies to ensure QoS. It supports synchronous/asynchronous base station

running mode, adopts uplink/downlink closed loop power control mode and

outer loop power control mode, and adopts the open loop and close loop

transmit diversity modes; it adopts QPSK for modulation in uplink and

downlink directions; it supports Turbo codes and convolutionary codes

3. Technical features of TD-SCDMA

The IMT-2000 CDMA TD adopts the TDD mode. It includes the UTRAN TDD

presented by Europe and the TD-SCDMA presented by China. In the IMT-2000,the TDD has its independent spectrum. It partially adopts the smart antenna and

uplink synchronization technologies. It is suitable for high-density low-speed

access, small-area coverage, and asymmetrical data transmission.

At present, Europe has given up UTRAN TDD, so TD-SCDMA is the only radio

transmission standard based on TDD. In March 2001, R4 was passed by the

3GPP, and TD-SCDMA was accepted as a formal standard. From the technical

features and market requirement, as a supplementary to the FDD mode, TD-

SCDMA has the development potential. However, only a few manufactures

participate in the R&D of the TD-SCDMA, which limits the application

prospect of the TD-SCDMA.

The TD-SCDMA integrates FDMA, TDMA, and CDMA. Its channel spacing is

extended to 1.6 MHz; its frame structure and timeslot structure are the same as

those of the GSM; its expansion factor is 16; it can support eight subscribers per

timeslot. Each timeslot supports only eight subscribers (code division), so the

joint detection can be used. In this case, the fast power control is not needed and

the inter-symbol interference is reduced. Besides, the TDD can also be used. The

mobile station (MS) will adopt dual-mode mobile phone for compatibility with

the network and signaling layers of the GSM.

The TD-SCDMA can smoothly evolve to the 3G, so it is supported by many

GSM suppliers.

1.3.2 Spectrum Allocation of IMT-2000

In 1992, the WRC allocates the following spectrum for the IMT-2000:

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Uplink band: 1885~2025 MHz; downlink band: 2110~2200 MHz;

Band for mobile satellite service: 1980~2010 MHz; 2170~2200 MHz;

As shown above, the uplink band and downlink band of the IMT-2000 are

asymmetrical. Therefore, some systems provide services by using asymmetric band in

TDD mode. However, the spectrum allocation of IMT-2000 is not considered the same

in different countries and regions, so the spectrum allocation is not fully followed in

different countries and regions.

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2 Structure and Evolution of the CN

2.1 Network Structure in Different Phases

The UMTS is the 3G mobile communication system that adopts WCDMA air interface.

In general, the UMTS is also called WCDMA communication system. The structure of

the UMTS is the same as that of the 2G mobile communication system. It includessome logical network units. Different network units can be grouped according to their

functions or subnetworks.

According to the function, the network units can be divided into radio access network

(RAN) and core network. The RAN processes all the radio-related functions; the CN

processes the switching and routing of all the voice calls and data connections in the

UMTS with the external networks. The RAN, CN, and user equipment (UE) constitute

the whole UMTS. The system architecture of the UMTS is shown below.

Terminal AN 3G CN External network

Service

applications

HLR,SCP

Fig. 2.1-1 Architecture of the UMTS

The general structure of the UMTS network is defined in 3GPP TS23.002. Currently,

the 3GPP has defined three versions of general structure for the UMTS network: R99,

R4, and R5.

During the evolution from R99 to R5, the logical classification of the CN remains



unchanged; it is still divided into CS and PS. In R5, the IP multimedia subsystem

(IMS) is added. The change to the NE entities is primarily shown in the MSC in R99.

In R4, the MSC is logically divided into MGW and MSC Server, and the transport

signaling gateway (T-SGW) and roaming signaling gateway (R-SGW) are added . In

R5, IMS is added based on the R4. Besides, the corresponding interfaces are added to

R4 and R5.

2.1.1 Network Structure of R99

Fig. 2.1 -2 shows the basic structure of the UMTS R99 network.

The CN is divided into CS and PS. The CS network units include MSC, VLR, and

GMSC. The PS network units include SGSN and GGSN. The HLR, AUC, and EIR are

common to the CS and PS.

The RAN includes radio network controller (RNC) and WCDMA BTS (Node B).

Besides, the CN PS connects with other PLMNs or PDNs through Gi and Gp

interfaces, and the CS connects with fixed networks and other PLMNs through the

PSTN.




Fig. 2.1-2 Basic Network Structure of R99

As shown in Fig. 2.1 -2, to protect the investment of the operators, the network

structure design of R99 fully considers the compatibility of 3G with 2G. The CN

inherits the NE entities defined in GSM/GPRS, enabling the current network to

smoothly evolve to the 3G. Therefore, the CN almost remains unchanged.

Corresponding interface protocols are added to some NEs to support 3G service, and

the original interface protocols are also improved. However, the UMTS terrestrial radio

access network (UTRAN, including RNC and Node B) is based on the WCDMA

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technology defined in R99), and its change is revolutionary.

2.1.1.1 Interfaces of the CN

1. Interfaces between CN and access network (AN)

1) Interfaces between CS and AN

· Interface between MSC and base station subsystem (BSS) (A)

· Interface between MSC and the radio network subsystem (RNS) (Iu_CS)

2) Interfaces between PS and AN

· Interface between SGSN and BSS (Gb)

· Interface between SGSN and RNS (Iu_PS)

2. Internal interfaces of the CN

1) Internal interfaces to the CS

· Interface between MSC and the related VLR (B)

· Interface between HLR and MSC (C)

· Interface between HLR and VLR (D)

· Interface between MSCs (E)

· Interface between MSC and EIR (F)

· Interface between VLRs (G)

2) Internal interfaces to the PS

· Interface between SGSN and HLR (Gr)

· Interfaces between SGSN and GGSN (Gn and Gp)

· Interface between GGSN and HLR (Gc)

· Interface between SGSN and EIR (Gf)

3) Interfaces used by PS and CS

· Interface between MSC/VLR and SGSN (Gs)

· Interface between HLR and AuC (H)

2.1.1.2 NE Entities of the CN

1. MSC/VLR

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As the core of the CN, the MSC is a functional entity that controls the MSs and

implements voice channel switching in the coverage area, it is also the interface

between the mobile communication system and the circuit-switched networks

such as PSTN, ISDN, and PSPDN. The MSC performs functions such as

network interface, common channel system, and charging. It also performs radio

resource management (SS7 and audio radio resources) and mobility

management between the RNS and the MSC. In addition, t set up a call route to

each MS, each MSC shall also perform the functions of the GMSC.

The VLR serves the mobile subscribers within its control area. It stores

information about the registered mobile subscribers that enter its the control area

(for example, subscriber number and location area identifier), which is necessary

for the setup of the call connection for the registered mobile subscribers. The

VLR acquires necessary information from the HLR of the mobile subscriber and

stores it. Once the mobile subscriber leaves the control area of the VLR, the

subscriber registers with another VLR, and the original VLR removes the

temporary data of the mobile subscriber. Therefore, the VLR is a dynamic user

database.

2. SGSN

The SGSN is the core of the PS. It traces the location of the MS, and performs

functions such as security authentication and access control. It also works with

the GGSN to set up, maintain, and release PDP connections. For the GSM BSS,

the SGSN connects with the GPRS BSS through the Gb interface; for the

WCDMA BSS, the SGSN connects with the RNS through the Iu interface.

The SGSN system provides the following functions:

1) Network access control

2) Packet routing and transfer

3) Mobility management

4) Logical link management (when Gb access is provided)

5) Radio resource management

6) Network management

3. GGSN

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The GGSN is a gateway that connects the CN PS with the external network. The

CN PS connects with the external packet-based networks through the GGSN. In

general, the external packet-based network refers to the X.25 network or the

Internet (TCP/IP). The X.25 network is not the development trend, so most of

the CN PS only provides interfaces to the Internet only.

The GGSN is one of the NEs introduced to enable the 3G network to provide

packet-based data service. It provides routing and encapsulation functions for

the packets between the 3G network and the external network. It can be

considered as the routing device in the 3G network that connects with the

external data network. Which GGSN is selected by the user is determined during

the activation of the PDP contexts according to the subscription information

about the user and the access point name (APN) requested by the user.

The GGSN provides the following functions:

1) Interfacing external IP packet-based network: The GGSN provides the gateway

function for the MS to access the external packet-based network. From the angle

of the external network, the GGSN functions like a router that can route packets

to all the user IP addresses in the GPRS network.

2) GPRS session management: It establishes and disconnects the communications

between MS and the external network.

3) Sending the packets received from the external data network to a proper SGSN

to transfer the packets to the MS.

4) Generating and outputting CDR: It shows the use of the external network by the

user.

4. HLR

As the data center of the system, the HLR stores information about all the

mobile subscribers that have registered with the HLR, including location

information, service data, and account management information. It supports

real-time modifying and querying of subscriber location information and various

service operations, including location updating, call processing, authentication,

supplementary service, and so on. It performs subscriber mobility management

in the mobile communication network..

One HLR can control several mobile switching areas. The HLR stores all

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important static data of the mobile subscribers; it also stores and provides the

dynamic information about the roaming area of the mobile subscribers for the

MSC.

5. AUC

The AUC performs security management for the GSM system. It stores

authentication information and keys to prevent unauthorized users to access the

system and to ensure the security of the mobile communication.

6. EIR

The EIR stores the IMEIs of the MSs. The operator can check the white list,

black list and gray list and then take measures to ensure the uniqueness and

security of each MS in the network. The white list contains the IMEIs of the

allowed MSs; the black list contains the IMEIs of the faulty MSs to be

monitored; the gray list contains the IMEIs of the stolen MSs that cannot be

used.

7. GMSC

The GMSC connects the CN CS and the PSTN. Through the GMSC, the CN CS

and the PSTN can interconnect with each other.

The GMSC provides physical connection for the interconnection between the

PSTN and the CS. Besides, when a PSTN subscriber calls a mobile subscriber,

the GMSC can acquire roaming number from the HLR. (Note that if the GMSC

refers to an MSC that can acquire roaming number from the HLR, all MSCs

have the functions of the GMSC. When a mobile subscriber calls another mobile

subscriber, the calling MSC acquires roaming number from the called HLR, so

all MSCs are GMSCs.)

2.1.1.3 NE Entities of the RNS

The RNS directly with the MS through the air interface (Uu). It transmits/receives

radio signals and manages radio resources. Besides the RNS connects with the MSC

and SGSN to set up communication connection between mobile subscribers and

between mobile subscriber and PSTN subscriber and to transfer system signals and

subscriber information. The RNS includes two parts: RNC and Node B.

1. RNC

RNC is the control part of the RNS. It manages various interfaces, radio

19




resources, and radio parameters. It connects with the MSC and SGSN through

the Iu interface. It terminates the protocol between the UE and the UTRAN.

2. Node B

Node B is the radio part of the RNS. Under the control of the RNC, the Node B

serves radio transceivers of a cell, completes the processing related to the

physical layer (channel coding, interleaving, rate matching, frequency spreading,

and so on), and performs radio resource management (for example, inner loop

power control).

3. UE

MS is the UE. There are vehicle mounted MS, portable MS, and hand-held MS.

The UE is independent of the mobile subscriber. All information related to the

subscriber is stored in the SIM card, which can be used in any MS. In the 2G,

the MS consists of ME and SIM card; in the 3G, the UE consists of ME, SIM,

and USIM. The ME is a raw terminal, through which the UE can interact with

the air interface of the BSS. The SIM stores the subscription data of 2G users.

The USIM stores the subscription data of the 3G users. A multi-mode UE can be

implement roaming and changeover between 3G and 2G networks.

4. UTRAN

The UTRAN is the radio access network of the UMTS. It consists of two or

more RNSs.


2.1.2.1 Overview

The R4 network is based on 3GPP TS23.002 V4.3.0 (2001.6). As with the R99

network, the R4 network also consists of CN (including CS and PS) and RAN, as

shown in Fig. 2.1 -3. Compared with the R99 network, the CS of the R44 changes,

while the PS almost remains unchanged.

The CAMEL entities and related interfaces of the R4 network almost remain

unchanged. The CAMEL function is enhanced based on R99; the definitions of the

interfaces and entities in the LCS architecture almost remain unchanged; the basic

functions of the network entities that have the same definitions as those in the R99

network almost remain unchanged, so do the related protocols.

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The following focuses on the changed network entities.

2.1.2.2 NE Entities

Compared with R99, the CS of the UMTS is changed. According to the concept of

separating call control from bearer, the (G)MSC in the R99 evolves to two parts in R4:

MGW and (G)MSC Server; the R-MGW and T-MGW are added; the related interfaces

are changed: the Mc interface between the MGW and the MSC Server, the Nc interface

between the MSC Server and GMSC Server, and the Nb interface between MGWs, and

the Mh interface between R-MGW and HLR.

The following describes the NEs in the CN and RAN of the R4.

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BSS

BSC

RNS

RNC

CN

Node B Node B

IuPS

Iur

Iub

USIM

ME

MS

Cu

Uu

MSC server

SGSN

Gs

GGSN GMSC

server

Gn HSS(HLR)

Gr

Gc C

D

Nc

H

EIR

F Gf

Gi PSTN

IuCS

VLR B

p

VLR

G

BTS BTS

Um

RNC

Abis

SIM

SIM-ME i/f or

MSC server

B

PSTN

cell

CS-MGW CS-MGW

CS-

MGW

AuC

Nb

T-SGW R-SGW

Mc Mc

Nb

PSTN PSTN

Nc

Mc

Mh

A Gb

E


Compared with basic structure of the R99, the structure of CN CS has changed much,

while the structures of the CN PS and UTRAN almost remain unchanged.

2.1.2.3 CN

In R4, the CN consists of the following NE entities: (G)MSC Server, CS–MGW, T–

SGW, R–SGW, SGSN, GGSN, HLR/AuC, EIR, and so on.

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1. MGW

The CS–MGW defines the MGW through media gateway of the CS domain.This section does not cover the IMS, so the concepts are not distinguished, and

the MGW is used to represent CS-MGW.

For a defined network, the MGW can be considered to be a terminating point of

the PSTN/PLMN transmission, including bearer and media processing devices

(for example, codec and echo compensation device).

The MGW can terminate a bearer channel of the SCN or a packet-based network

(for example, the RTP stream in the IP network).Through the Iu interface, the

MGW can support media conversion, bearer control, and payload processing

(codec and echo compensation device) to support different Iu interface options

(based on AAL2/ATM or RTP/UDP/IP) of the CS.

The MGW has the following functions:

1) Interacting with the MSC Server and GMSC Server for resource control;

2) Providing and processing resources, for example, echo compensation device;

3) Containing a codec;

4) Providing resources for supporting UMTS/GSM transmission media. The bearer

control and payload processing capability of the MGW must support mobility-

specific functions, for example, RNS relocation/changeover.

2. MSC Server

The MSC Server consists of the call control part and mobility control part of the

R99 MSC.

The MSC Server controls the MO and MT calls in the CS. It terminates the user-

to-network signaling and converts it to network-to-network signaling.

The MSC Server also contains a VLR for storing the subscription data of the

mobile subscribers and the CAMEL-related data.

The MSC Server controls the call states over the media channels of the MGW.

3. GMSC Server

The GMSC server consists of the call control part and mobility control part of

the R99 GMSC.

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4. T–SGW

If the CS transmission is based on IP, the IP signaling need be processed. As asignaling gateway, the T–SGW converts the signaling between 3G–CN and

PSTN/ISDN.

5. R–SGW

The R–SGW converts the signaling between 2G PLMN and 3G PLMN.

6. SGSN, GGSN, HLR/AuC, and EIR

These NE entities are similar to those in R99.

2.1.2.4 UTRAN

The structure of the RAN in R4 is the same as that of the RAN in R99, so it is omitted

here.

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2.1.3.1 Overview


Fig. 2.1 -4 shows the basic network structure of the UMTS in R5. R5 inherits the

definitions of the NE entities from R4, but their functions are enhanced. As stated

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earlier, the IMS is added to R5. Therefore, the corresponding interfaces between the

basic network and the IMS are added. As shown in Fig. 2.1 -4, in R5, the BSC is

required to provide Iu-CS and Iu-PS interfaces, which is the major difference between

the R5 network and the R4 and R99 networks. Besides, in R5, the HSS entity is added

to replace HLR. Compared with the HLR, the HSS provides more powerful functions

and supports the IMS.

2.1.3.2 NE Entities

In R5 CN, in addition to the change to the basic structure, the IMS entity is also added,

namely, an IMS taking CSCF as the core is formed. The purpose of the IMS is to

transfer various media streams (voice, data, image, and so on) over the IP network.

The IMS contains all the related entities necessary to the provision of the IP

multimedia service. As shown in Fig. 2.1 -5, the IMS contains network entities such as

CSCF, BGCF, MGCF, IM-MGW, and HSS MRF.

Fig. 2.1-5 IMS

Call state control function (CSCF): The CSSF can be used as proxy CSCF (P-CSCF),

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serving CSCF (S-CSCF), and interrogating CSCF (I-CSCF). The P-CSCF is the first

point for the UE to access the IMS; the S-CSF processes the network session states; the

I-CSCF is the access point of the network.

Media gateway control function (MGCF): The MGCF contains the call state control

part of the connection control of the media channel in the IM-MGW. It communicates

with the CSCF, selects CSCF according to the route number, converts call control

protocols between the ISUP and the IMS, and forwards the received outband

information to the CSCF/IM-MGW.

IP multimedia – media gateway function (IM-MGW): The IM-MGW can terminate the

media streams from the bearer channels of the SCN and from the packet-switchednetwork. It supports media conversion, bearer control, and payload processing. It can

interact with the MGCF for resource control. It can use and process resources (echo

compensation device). It can contain a codec.

Multimedia resource function controller (MRFC): The controls the media stream

resources in the MRFP, interprets the information from AS and S-CSCF, controls the

corresponding MRFP, and generates CDRs.

Multimedia resource function processor (MRFP): The MRFP controls Gi interface

bearer control and processes the resources provided by the MRFC, mixed access media

streams, media streams, and media stream resources.

Breakout gateway control function (BGCF): If the relay selected by the BGCF is

within the same network, the BGCF selects an MGCF for interaction with the PSTN. If

the relay is within another network, the BGCF forwards the related signaling to a

BGCF or MGCF in the corresponding network, depending on the configuration

performed by the operator of another network. The BGCF can select a network for the

relay purpose according to the information received by other protocols or the

information entered by the operator.

Home subscriber server (HSS): Compared with the HLR, the HSS provides more

powerful functions, supports more interfaces, and can process more subscriber

information.

The HSS can process the following information:

· Subscriber ID and address information;

· Subscriber security information---the network access control information used

27




for authentication and authorization;

· Subscriber location information---The HSS can register and store subscriber location information;

· Subscriber list information.

The HSS provides these functions: IP multimedia function, HLR functions necessary to

PS, HLR functions necessary to CS, and so on.

2.1.3.3 Radio Interfaces

1. Iu-BS between BSS and CN

This interface complies with the UMTS 25.41x specifications. It is used to

transfer information related to BSS management, call processing, and mobility

management. Its functions are the same as those of the Iu-CS interface between

the RNS and the CN.

2. Iu-PS between BSS and CN

This interface complies with the UMTS 25.41x specifications. It is used to

transfer data packets and the information related to mobility management. Its

functions are the same as those of the Iu-PS interface between the RNS and the

CN.

2.2 Evolution Characteristics

1. Use of the WCDMA technology in the RAN

In the R99, the CN consists of CS and PS. The CS is based on the circuit core

network of GSM Phase 2+; the PS is based on the GPRS CN. From the angle of

the CN subsystem, the major differences between the UMTS R99 CN and the

GSM/GRPS CN include the difference between the Iu interface and the A

interface, and CAMEL difference, and service difference.

2. Separation between service control and service implementation

After the R99 network evolves from the R4, the structure of the CN has changed

much, but the structure of the UTRAN almost remains unchanged. The R99 CN

consists of two domains CS and PS. The IP domain is based on the IP

transmission, so R4 focuses on the IP transmission of the CS. Based on the

concept of separation between service control and service implementation, when

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the R99 evolves to the all-IP network, the (G) MSC in the CS is divided into two

entities: MGW and (G)MSC Server. As a media access gateway, the MGW

connects, transfers, and converts various service streams. The MSC Server

implements service control and signaling processing. The (G) MSC Server

interconnects with the MGW through Mc interface to control the connection,

transferring, and conversion of various service streams.

3. Integration of wired IP and wireless IP

R5 network is a real all-IP network. Both the CN and the RAN are based on IP

transmission, and various media streams can be transferred over IP. Besides, the

network entities like IMS are also added to the CN. The IMS implements callcontrol function for the all-IP network..

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