Basic Technology of WCDMA

7/30/2019 Basic Technology of WCDMA

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Basic Technology of WCDMA

ZTE CORPORATIONZTE Plaza, Keji Road South,Hi-Tech Industrial Park,Nanshan District, Shenzhen,P. R. China

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Contents

Chap t er 1 ........................................... 1

Over v iew of W CDMA ......................... 1

Overview ....................................... 1

WCDMA Technical StandardsDevelopment Trends ....................... 4

3GPP Standard Development Status 5

Analysis on 3GPP standard Version

Evolution ..................................... 8

Analysis on Evolution of 3GPP

Technologies .............................. 10IMT2000 Frequency Band Allocation 19

Composition of WCDMA System ...... 20

UE (User Equipment ) .................. 21

UTRAN (UMTS Terrestrial RadioAccess Network ) ........................ 21

CN (Core Network) ...................... 23Chap t er 2 ......................................... 27

W CDMA Techn olog y Basics ............. 27

Concept of WCDMA RealizingBroadband Communication ............ 27

Basic Concepts of CDMA .............. 29


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Basic Concepts of Spread SpectrumCommunication ........................... 33

Transmission of Electric Waves inMobile Environment ....................... 38

Features of Land MobileCommunication Environment ........ 39

Signal Fading in Radio Path .......... 40

Fundamentals of the WCDMA

Technology ................................... 41

Channel Coding/Decoding ............. 41

Principles ofInterleaving/Deinterleaving .......... 43

Spread Spectrum ........................ 44

Modulation and Demodulation ....... 47

Key Technologies on WCDMA Wireless

Side ............................................. 48

Power Control ............................. 48

Handover ................................... 53

RAKE Receiver ............................ 63

Code Resource Allocation ............. 64

Admission Control ....................... 78

Load Control/Congestion Control ... 81

Overview and Features of AMR ........ 83

Chap t er 3 ........................................ 85

I n t er face Prot ocol and Channel

St ruct ur e of W CDMA RAN ....... .. .. .. .. 85


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-iii-

General Protocol Module for LandInterfaces of UTRAN ...................... 87

Horizontal Plane ......................... 88Vertical Plane ............................. 88

Iu Interface ................................ 90

Iur Interface .............................. 92

Iub Interface .............................. 93

Air Interface (Uu Interface) ............ 94

Physical Layer Protocol ................ 95

MAC Protocol .............................. 96

RLC Protocol............................... 97

PDCP ......................................... 98

BMC Protocol .............................. 99

RRC Protocol .............................. 99

Channel Classification ................ 100

Physical Channel ....................... 101

Transport Channel .................... 101

Logical Channel ........................ 102


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Confidential and Proprietary Information of ZTE CORPORATION 1

Overview of WCDMA

C h a p t e r 1

Overview

The 3rd Generation Mobile Communication System(3G) is put on agenda when the 2nd generation (2G)digital mobile communication market is booming. The

2G mobile communication system has the followingdisadvantages: limited frequency spectrumresources, low frequency spectrum utilization, andweak support for mobile multimedia services

(providing only speech and low-speed data services).

Also, thanks to incompatibility between 2G systems,the 2G mobile communication system has a lowsystem capacity, hardly meeting the demand for

high-speed bandwidth services and impossible for thesystem to implement global roaming. Therefore, the3G communication technology is a natural result in

the advancement of the 2G mobile communication.

As the Internet data services become increasingly

popular nowadays, the 3G communication technologyopens the door to a brand new mobile communicationworld. It brings more fun to the people. In addition toclearer voice services, it allows users to conduct

multimedia communications with their personalmobile terminals, for example, Internet browsing,multimedia database access, real-time stock quotes

query, videophone, mobile e-commerce, interactivegames, wireless personal audio player, video


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ential and Proprietary Information of ZTE CORPORATION

transmission, knowledge acquisition, andentertainments. What more unique are location

related services, which allow users to know about

their surroundings at anytime anywhere, forexample, block map, locations of hotels and supermarkets, and weather forecast. The 3G mobile phone

is bound to become a good assistant to peoples lifeand work.

The 3G mobile communication aims at meeting thefuture demand for mobile user capacity and providing

mobile data and multimedia communication services.Initially, mobile communication technologies weredeveloped separately, as various countries andtechnical organizations continued to develop their

own technologies. Thus, the USA has AMPS, D-AMPS,IS-136, and IS-95, Japan has PHS, PDC, and the EUhas GSM. On one hand, this situation helped to meet

the needs of the users at the early stage of mobile

communication and expand the mobilecommunication market. On another hand, it createdbarriers between the regions, and made it necessary

to unify the mobile communication systems globally.Under such a context, ITU launched thestandardization of the 3G mobile communicationsystem in 1985.

The 3G mobile communication system, IMT-2000, isthe general term for the next generation

communication system proposed by ITU in 1985,when it was actually referred to as Future Public LandMobile Telecommunications System (FPLMTS). In1996, it was officially renamed to IMT-2000. In

addition, the 3G mobile communication technologyextends the integrated bandwidth network service as

far as it can to the mobile environment, transmitting


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Chapter 3 Interface Protocol and Channel Structure of WCDMA RAN


multimedia information including high quality imagesat rates up to 10 Mbps.

Compared with the existing 2G system, the 3Gsystem has the following characteristics assummarized below:

1. Support for multimedia services, especially Internetservices

2. Easy transition and evolution

3. High frequency spectrum utilization

Currently, the three typical 3G mobile communication

technology standards in the world are CDMA2000,WCDMA and TD-SCDMA. CDMA2000 and WCDMAwork in the FDD mode, while TD-SCDMA works in theTDD mode, where the uplink and downlink of the

system work in different timeslots of the samefrequency.

The 3G mobile communication is designed to providediversified and high-quality multimedia services. Toachieve these purposes, the wireless transmission

technology must meet the following requirements:

1. High-speed transmission to support multimedia

services

Indoor environment: >2 Mbps

Outdoor walking environment: 384 Mbps

Outdoor vehicle moving: 144 kbps

2. Allocation of transmission rates according to needs

3. Accommodation to asymmetrical needs on theuplink and downlink

In the concept evaluation of the 3G mobile

communication specification proposals, the WCDMAtechnology is adopted as one of the mainstream 3G


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technologies thanks to its own technicaladvantages.

WCDMA Technical Standards Development Trends

WCDMA was originated by standardization

organizations and manufacturers in Europeancountries and Japan. WCDMA inherits the highstandardization and openness of GSM, and itsstandardization progresses smoothly. WCDMA is the

third generation mobile communication standard

developed by 3GPP, with the GSM MAP as its coreand UTRAN (UMTS Terrestrial Radio Access Network)

as its wireless interface. Using the chip rate of 3.84Mbps, it provides data transmission rate up to 14.4Mbps within 5 MHz bandwidth.

The WCDMA technology has the followingcharacteristics:

Supporting both asynchronous and synchronousBTSs, for easy and flexible networking

Using QPSK modulation mode (the HSDPA servicesalso use the 16QAM modulation mode)

Using pilot assisted coherent demodulation

Accommodating transmission of multiple rates, andimplementing multi-rate and multimedia servicesby changing the spread spectrum ratio and usingmulti-mode concurrent transmission

Rapid and efficient power control ofuplink/downlink greatly reduces multiple access

interference of the system, but increases thesystem capacity while reducing the transmissionpower.


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The core network is evolving based on theGSM/GPRS network, and maintains compatibilitywith the GSM/GPRS network.

Supporting soft handover and softer handover, withthree handover modes, inter-sector soft handover,inter-cell soft handover, and inter-carrier hard

handover

3GPP Standard Development Status

3GPP standard versions include R99, R4, R5, R6 andR7.

R99 version was frozen formally in Mar, 2000, andrefreshes once every three months. Currentcommercial version of R99 is based on the version of

June, 2001, for in later version, the number ofCR isdecreasing rapidly and there are no larger

modifications and non-compatible upgrade.R4 version was frozen in Mar, 2001. It passed in Mar,2002 and is stable currently. R5 version was frozen in

June, 2002 and is stable currently. Most R5 versionsthat providers support are the version of June, 2004.R6 version was frozen in June, 2005 and may bestable in a year. At present, R7/LTE has started up

and its functional features are still in initial phase.

R99 and R4 versions are put into commercial use

maturely. R6 version protocols are in developingstatus.


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Basic Network Structure Based on R99

FIGURE 1 BASIC NETWORK STRUCTURE OF R99

The R99 is the first phase version of 3GPP in 3Gnetwork standardization. The R99 was already frozen

in June 2001, and subsequent revision is made onthe R4. The basic configuration structure of the R99is illustrated in Figure 1. To guarantee the investment

interests oftelecom operators, the network structure


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of the R99 is designed with 2G/3G compatibility fullyin mind, for smooth evolution to 3G. Therefore, thecore network in the basic network structure remainsunchanged. To support 3G services, some NEs are

added with appropriate interface protocols, and theoriginal interface protocols are also improved bydifferent degrees.

Network Structure Based on UMTS R4

Same as the R99 network, the basic structure of theR4 network consists of the core network and wirelessaccess network, and there are the CS domain and PSdomain on the core network side. The basic NEentities and the interfaces are largely inherited from

the definitions of entities and interfaces of the R99network. The network entities with the samedefinitions as the R99 network remain unchanged in

basic functionality, and the related protocols are alsosimilar.

Compared with the R99, the R4 network structurehas tremendous changes in the structure of the CSdomain of the core network, while those of the PSdomain of the core network and of the UTRAN also

remain the same.

According to the idea of separation between callcontrol, bearer and bearer control, the network entity(G) MSC of the CS domain of the R99 networkevolves to the MGW and (G) MSCServer in the R4stage, with R-SGW and T-SGW added. In addition,

related interfaces are also changed, with the Mcinterface added between the MGW and MSC Sever,the Nc interface between the MSC Sever and GMSC


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Sever, and the Nb interface between MGWs, and theMh interface between the MR-MGW and HLR.

FIGURE 2 BASIC NETWORK STRUCTURE OF THE R4

BSS

BSC

RNS

RNC

CN

Node B Node B

IuPS

Iur

Iub

USIM

ME

MS

Cu

Uu

MSC serverSGSN

Gs

GGSNGMSC

server

GnHSS(HLR)

Gr

GcC

D

Nc

H

EIR

F Gf

GiPSTN

IuCS

VLRB

Gp

VLR

G

BTSBTS

Um

RNC

Abis

SIM

SIM-ME i/f or

MSC server

B

PSTN

cell

CS-MGWCS-MGW

CS-

MGW

AuC

Nb

T-SGW R-SGW

McMc

Nb

PSTNPSTN

Nc

Mc

Mh

AGb

E

Analysis on 3GPP standard Version Evolution

During the evolution from GSM/GPRS to 3GPP R99,

brand UTRAN introduced includes such key


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technologies as WCDMA, power control, multipathRake receiver. In addition, four QoS service types areput forward and cell peak rate supports up to 2 Mbps.CN basically develops from GSM/GPRS CN. It reduces

the influence on GSM/GPRS CN caused by theintroduction of UTRAN CN furthest. Mostrepresentative features of R4 from R99: Separation

of CS domain control layer and transmission layer,convergence of transmission resources in CS and PSdomains, and increase of resource transmission

efficiency.UTRAN in R4 version does not have substantiveevolution and only performs some optimizations.

During the evolution from R4 to R5, IP multimediasubsystem is introduced into CN and the interface

connecting GERAN is added. There is great change inUTRAN: IP transmission technology and HSDPA are

introduced, which makes peak rate of the cell up toabout 10 Mbps, much greater than the peak

bandwidth that R4 and R99 versions can support (inthe field, WCDMA supporting HSDPA is called 3.5 G).R5 also supports Iu Flexible, allowing a RNC to accessseveral MSCs or SGSNs simultaneously, which saves

investment on access network resources foroperators.

intercommunication of WLAN and UMTS. UTRANevolution includes: MBMS, HSUPA, enhanced HSDPA,wave cluster figuration technology to increase

coverage capacity, 3GPP RET and MOCN.

In R7 plans. WCDMA will be developing in total IP

direction. In addition, intercommunication of UTMSwith other networks (such as, VLAN) and enhanced

MBMS will be increased.


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dential and Proprietary Information of ZTE CORPORATION

Analysis on Evolution of 3GPP Technologies

Evolution of CN Technology

Total IP CN

Brand UTRAN is introduced in initial phase of 3GPPR99, to reduce the influence of UTRAN on CN.Introduction policy of CN is developed from

GSM/GPRS CN.

During the evolution from R99 to R4, CN realizes

the separation of CS domain control layer andtransmission layer, realizes voice packet andsignaling packet, transmits CS and PS domainsapplication in CN based on one IP.

During the evolution from R4 to R5, 3GPP CNintroduced IMS based on packet domain. IMS

adopts Session Initiation Protocol (SIP) that IETFdefines and provides IP services that Qos issensitive to (such as, VoIP) in packet switchingdomain, to intercommunicate fixed IP terminal and

3G mobile terminal.

In R6 version, functions of IMS are enhanced

greatly, including the intercommunication of localIP multimedia network and other IP multimedianetworks, intercommunication of IMS and CS,

intercommunication of IMS based on IPV4 andIPV6, multi-party conference service, IMS groupmanagement and SIP appended to IMS. As aresult, wider and more flexible IP-based multimedia

services are provided for operation.

During the evolution from R99 to R7, CN may

absolutely abandon circuit switching domain in the

future and develops into a total IP service mobilenetwork.


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Network sharing

In 3GPP R99/R4, one RNC can only connect one

MSC or SGSN, resulting in low utilization ratio ofresources.

In R5, Iu-Flex is introduced between CN andUTRAN, realizing the UTRAN resources sharingamong several nodes of one operator. It saves thecost on UTRAN and substantially develops the

network sharing technology.

In R6, network sharing function is expandedcontinuously, which provides the configurationmode of Multiple Operator Core Network (MOCN).MOCN allows several operators to share one radio

access network in sharing area. As a result,operators can save investment on UTRAN.

Amalgamation with other networks

In 3GPP R6, intercommunication and amalgamationof UMTS and WLAN are fulfilled (Phase I), which isstrengthened in R7 plans (Phase II). In addition, inR7, defines feasibility of total IP network operation.Intercommunication and amalgamation of CN with

other networks is future development trend.

Evolution of Radio Access Network Technologies

High-speed broadband access

Compared with GSM/GPSR RAN, R99 introducednew UTRAN. UTRAN is based on WCDMA radiointerface technology. Its signal bandwidth is 5 MHz.Its code chip rate is 3.84 Mbps. Its cell downlink

service bandwidth is about 2 M.

R4 version has no large change in radio access.


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In R5 version, HSDPA is introduced. It adopts 16QAM modulation mode, which greatly increases

spectrum utilization ratio. Cell downlink peak rate

reaches 14 Mbps. In the field, the systemsupporting HSDPA is defaulted as 3.5 G system.

In R6 version, HSUPA is introduced, which makescell uplink peak rate up to 5.7 Mbps.

In R7 version, Multiple Input Multiple Output(MIMO) antenna technology is introduces, whichenables several transmitting and receiving

antennas to send and receive signals in sameband. As a result, system capacity and spectrumutilization ratio is increased in germination. MIMOantenna technology meets the requirements for

high speed services in future mobilecommunication system. In Long Term Evolution(LTE) items, Orthogonal Frequency Division

Multiplexing (OFDM) is introduced, which makes

cell downlink peak rate up to 39 Mbps. It maydevelop as the core technology base of 3Gadvanced system (such as, Beyond 3G, 3.9G and

E3G). With continuous development of 3GPPstandardization, OFDM will be applied tobroadband mobile communication field morewidely in the near future.

In the future, MIMO and OFDM technologies willcombine. System test results improve that

MIMO-OFDM system which has two transmissionantennas and two receiving antennas can providethe data transmission rate from score to a hundredmillion.

In a word, evolution process of radio access

network on accessbandwidth is: 2 Mbps (R99)

HSDPA DL 14 Mbps (R5) HSDPA DL 14


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Mbps/HSUPA UL 5.7 Mbps (R6) --> MIMO (R7) OFDM (LTE). Its evolution is to introduce all kindsof technologies, increasing spectrum utilizationratio furthest and meeting the requirements for

high speed data transmission.

Mobile management

From R99 version, WCDMA has differences fromGSM/GPRS in mobile management, including soft

handover, Iur interface, re-positioning, handoverand reselection between 2/3G. From R4 version,Iur interface has introduced such flows as public

measurement and radio link congestion, whichmakes radio resource management and loadcontrol of Iur interface be organic part of UTRAN.At the same time, amalgamation criteria with

GERAN are under way, including Iur-g, cell changethat network aids.

IP transmission

UTRAN in R99/R4 versions adopts TDM and ATM.

CN in R4 version successfully introduces the baseofIP transmission technology.

3GPP UTRAN in R5 version also introduces IPtransmission technology. IP transmission is aselective technology of UTRAN and it makes UTRAN

transmit based on IP core switching network. As aresult, flexibility of transmission networking isincreased and construction cost of operators isreduced. IP transmission is also UTRAN

transmission development trend.

In transmission, R4/R5 versions added

transmission bearer modification and

reconfiguration, to further optimize theperformance of transmission bearer.


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Antenna technology

During the evolution of 3GPP standards, 3GPP alsohas evolution in antenna technology and antenna

evolution process is: Two projects of wave clusterfiguration (R5) Fixed wave cluster figurationproject and 3GPP electronic modulation antenna(R6) MIMO (R7).

The evolution is to improve link performance of thesystem by introducing all kinds of antennatechnologies, increasing system capacity.

In R5 version, radio wave cluster figurationtechnology is introduced to increase system link

performance and capacity. Two projects are putforward: fixed wave cluster figuration and userspecial wave cluster figuration. In R6 version, userspecial wave cluster figuration project is deleted

and fixed wave cluster figuration project is

decided.In mobile BS network planning and optimization,common measure is to remotely modulateantennas of BS system. Most operators purchase

antennas from third party. In these years, AntennaInterface Standard Group (AISG) has put forwardAISG interface standards. However, since 3GPPdoes not definite antenna interfaces in R99/R4/R5

phases, it is difficulty for manufacturers to havesame antenna interface, antenna type and networkoptimization. Therefore, in R6 version, 3GPPuniforms interface of RET and introduces Iuant

antenna interfaces. Standardization of RETinterfaces makes remote network optimizationpossible on condition that several manufacturers

provide antennas.


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In R7 version, 3GPP puts forward MIMO, whichincreases system capacity and spectrum utilizationratio in germinations. Although MIMO is notmature at present, it is a great breakthrough of

antenna technology in mobile communication fieldand also a developing direction of future intelligentantenna technology.

Positioning technology

In R99 version, UE positioning technology based oncell ID is introduced. It is a rough positioningtechnology. In R99 version, frames ofOTDOA and

A-GPS are introduced, too.

In R4 version, criteria of Iub/Iur interfaces are put

forward, which improves OTDOA and A-GPSpositioning technologies.

In R5 version, criteria of SMLC-SRNC interfaces areput forward and they are open to support A-GPSpositioning technology (not supporting otherpositioning technologies).

In R4 and R5, lowest performance requirements forA-GPS measurement are not given. Therefore, in

R6 version, positioning precision of A-GPS isdefined (positioning range of a mobile station is 30to 100 m and response time is 2 to 20 s. In R6

version, SMLC-SRNC interfaces are open to supportthree positioning technologies (CellID, OTDOA andA-GPS).

In R7 version, Uplink-Time Difference Of Arrival(U-TDOA) is put forward. It is hoped to providesolutions that are more flexible and whose

positioning precision is higher.


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The evolution process of positioning technology is:Cell ID OTDOA AGPS U-TDOA. It is a

process from rough positioning technology to the

positioning technology with high precision. Allpositioning technologies can be supplements toeach other during the application.

Evolution of UMTS QoS Technology

With the close combination of radio communication

technology and IP technology, mobile communication

network develops from circuit switching network ofGSM to packet switching network of GSM, and to 3G,

3.5G and UMTS that provide high speed real-timedata services. During the whole evolution of mobilenetwork, QoS technology develops to mature toprovide satisfactory services according to features of

different services. Analysis on QoS in GSM, GPRS,R99, R4, R5, R6 and R7 tell development of mobilenetwork QoS.

GSM is based on circuit switching mode. It is simple.Connection of circuit can ensure QoS. GSM defines aseries of circuit bearer services, including parameters

of synchronization/asynchronization,transparent/non-transparent, and limited bit rate set.They are continuously effective during the evolution

of mobile network.

GPRS is based on packet switching mode. There is noConnection concept in GPRS, so QoS assurance of

GPRS is more complicated than that of GSM. QoSparameters that GPRS defines are: Delay level,confidence level, largest data flow, PRI, even data

flow and retransmission demand. QoS parameters

can be transmitted between UE and SGSN/GGSN.


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QoS of UMTS is to provide end-to-end assurance ofservices, which is introduced in R99 version, asshown in Figure 3. End-to-end QoS covers all NEs,including user terminal, access network entity and CN

entity. Processing of different interface QoSparameters must be same. The introduction of QoSlayered architecture is a large advancement during

the QoS evolution.

FIGURE 3 QOSFRAME OF UMTS

TE CN

Gateway

MT UTRAN CN Iu

EDGE

NODE

TE

End-to-End Service

TE/MT Local

Bearer ServiceUMTS Bearer Service

External

Bearer Service

Radio Access Bearer Service CN BearerService

Radio

Bearer Service

Iu

Bearer Service

Backbone

Bearer Service

UTRA

FDD/TDD

Service

Physical

Bearer Service

UMTS

Operators decide the bearer mode that UMTS CN

adopts. Its circuit domain can support TDM and ATMbearing modes (in R4 and later version, transmissionand control in circuit domain is separated and IPtransmission is selective). Its packet domain supportsIP bearer. TDM and ATM bearers both provide QoS

assurance. IP bearer of CN adopts the QoStechnology that IETF defines, including integratedservice/resource preservation (IntServ/RSVP),

Multiple Protocol Label Switching (MPLS), Differential


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Service (DiffServ), flow project and constraint-basedpath seek, and so on.

In R99 version, four QoS types are introduced:

Conversational, data streaming, interactive andbackground. It also defines QoS parameters morethan GSM and GPRS. There are new requirements fortransmission delay, retransmission mechanism, jitterand code error rate of above four types.

In R4 version, QoS that AAL2 connects on Iub and Iuris optimized, to improve real-time services support.

In addition, QoS negotiation mechanism of radioaccess bearer is introduced to make use of radioresources more effectively and to enhance theconstruction capability of radio access bearer.

In R5 version, intercommunication and combinationof UE local bearer service, GPRS bearer service and

outer bearer service are defined. They provide QoS

assurance for end-to-end services in packet domain.In UE and GGSN, IP BS Manager may exist. It usually

uses DiffServ and IntServ/RSVP to communicate withouter IP network. IMS, which is QoS policy controlmechanism based on services, is also introduced inR5 version.

In R6 version, QoS policy control mechanism basedon services is evolved as an independent functional

entity, providing services in all packet domains withQoS policy control mechanism based on services. Thismechanism separates control and execution of QoS.Network administrator can consider the whole

network, without paying attention to details, such as,technology and equipment. It reflects the intelligentmanagement of QoS.


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In R7 version, amalgamation of UTMS and WLAN isput forward. Uniform IP QoS is what future UMTSQoS technology will develop to.

Evolution process of QoS is: QoS parameters do nottransmit in the network (GSM) QoS parameterstransmit between UE and SGSN/GGSN Number of

QoS parameters increase (GPRS) QoS layeredarchitecture, four QoS types, QoS that IETF defines,all NEs that QoS parameters cover, new change in

parameters, the number of parameters increase

(R99) QoS negotiation mechanism of radio accessbearer (R4) QoS policy control mechanism based

on services in IMS (R5) QoS policy control

mechanism based on services in all packet domain(R6) Uniform IP QoS in the amalgamation of UMTSand WLAN (R7 and later version).

IMT2000 Frequency Band AllocationIn 1992, World Radio-communication Conference(WRC-92) allocated the frequency bands for the 3G

mobile communication, with a total bandwidth of 230MHz, as shown in Figure 4.


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In terms of functions, the network units comprise theRadio Access Network (RAN) and Core Network (CN).The RAN accomplishes all the functions related toradio communication. The CN handles the exchange

and routing of all the calls and data connectionswithin the UMTS with external networks. The RAN,CN, and the User Equipment (UE) together constitute

the whole UMTS.

UE (User Equipment )

The UE is an equipment which can be vehicle installedor hand portable. Through the Uu interface, the UEexchanges data with network equipment and provides

various CS domain and PS domain services, includingcommon voice services, broadband voice services,mobile multimedia services, and Internet applications(such as E-mail, WWW browse, and FTP).

UTRAN (UMTS Terrestrial Radio Access Network )

The UMTS Terrestrial Radio Access Network (UTRAN)comprises Node B and Radio network Controller(RNC).

1) Node B1.

As the base station (wireless transceiver) in theWCDMA system, the Node B is composed of thewireless transceiver and baseband processing part.Connected with the RNC through standard Iub

interface, Node B processes the Un interfacephysical layer protocols. It provides the functions ofspectrum spreading/despreading,

modulation/demodulation, channel


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coding/decoding, and mutual conversion betweenbaseband signals and radio signaling.

2) RNC

The RNC manages various interfaces, establishesand releases connections, performs handoff andmacro diversity/combination, and manages and

controls radio resources. It connects with the MSCand SGSN through lu interface. The protocolbetween UE and UTRAN is terminated here.

The RNC that controls Node B is called Controlling

RNC (CRNC). The CRNC performs load control andcongestion control of the cells it serves, and

implements admission control and code wordallocation for the wireless connections to beestablished.

If the connection between a mobile subscriber andthe UTRAN uses many RNS resources, the related

RNC has two independent logical functions:Serving RNC (SRNC). The SRNC terminates thetransmission of subscriber data and the Iu

connection of RANAP signaling to/from the CN. Italso terminates the radio resource controllingsignaling (that is the signaling protocol between UE

and UTRAN). In addition, the SRNC performs L2

processing of the data sent to/from the radiointerface and implements some basic operationsrelated to radio resources management.

Drift RNC (DRNC) All the other RNCs except the SRNCare DRNCs. They controls the cells used by the UEs.


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CN (Core Network)

The CN is in charge of the connections with othernetworks as well as the management and

communication with UEs. The CN can be divided intoCS domain and PS domain from the aspect of logic.

The CS domain equipment refers to the entities thatprovide circuit connection or related signalingconnection for subscriber services. The specific

entities in the CS domain include:

1. Mobile switching center (MSC)

2. Gateway mobile switching center (GMSC)

3. Visitor location register (VLR)

4. Interworking function (IWF).

The PS domain provides packet data services tosubscribers. The specific entities in the PS domain

include:5. Serving GPRS support node (SGSN)

6. Gateway GPRS support node (GGSN)

Other equipment such as the home locationregister (HLR) or HSS, authentication center (AuC),and equipment identity register (EIR) are shared

by the CS domain and PS domain.

The major functional entities are as follows:

1) MSC/VLR

As the functional node in the CS domain of theWCDMA core network, the MSC/VLR connects withthe UTRAN through Iu CS interface, with external

networks (PSTN, ISDN, and other PLMNs) through

PSTN/ISDN interface, with the HLR/AUC throughC/D interface, with the MSC/VLR, GMSC or SMC


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ogy of WCDMA


through E interface, with the SCP through CAPinterface, and with the SGSN through Gs interface.

The MSC/VLR accomplishes call connection,

mobility management, authentication, andencryption in the CS domain.

2) GMSC

As the gateway node between the CS domain ofWCDMA network and external networks, the GMSC

is an optional entity. It connects with the externalnetworks (PSTN, ISDN, and other PLMNs) through

PSTN/ISDN interface, with the HLR through Cinterface, and with the SCP through CAP interface.

The GMSC accomplishes the incoming and outgoingrouting of the Visited MSC (VMSC).

3) SGSN

As the functional node in the PS domain of WCDMAcore network, the SGSN connects with the UTRANthrough Iu_PS interface, with GGSN through Gn/Gp

interface, with the HLR/AUC through Gr interface,with the MSC/VLR through Gs interface, with theSCP through CAP interface, with the SMC throughGd interface, with the CG through Ga interface, and

with the SGSN through Gn/Gp interface.

The SGSN accomplishes the routing forward,

mobility management, session management,authentication, and encryption in the PS domain.

4) GGSN

The GGSN connects with the SGSN through Gn

interface and with the external data networks(Internet /Intranet) through Gi interface.

The GGSN provides routes to the data packetsbetween the WCDMA network and external data


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networks, and encapsulates these data packets.The major function of the GGSN is to provide theinterface to the external IP packet-based network,thus the UEs can access the gateway of the

external packet-based network. To the externalnetworks, the GGSN seems like the IP router thatcan be used to address all the mobile subscribers in

the WCDMA network. It exchanges routinginformation with external networks.

5) HLR

The HLR connects with the VMSC/VLR or GMSC

through C interface, with the SGSN through Grinterface, and with the GGSN through Gc interface.The HLR stores subscriber subscription information,supports new services, and provides enhanced

authentication.


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WCDMA Technology Basics

C h a p t e r 2

Concept of WCDMA Realizing Broadband

Communication

WCDMA (Wideband CDMA) is CDMAradio communication mode cased ondirect spread-spectrum technology.

WCDMA has an obvious advantage overGSM and IS-95 in subscriber capacityand radio transmission performance, for

it adopts a series of key technologies.WCDMA bears following two meaningsliterally:

1. WCDMA adopts CDMA communicationtechnology1.

CDMA technology is the mostadvanced communication technology

in the world at present. It takesadvantage of different codes to dividedifferent channel and then distinguishdifferent subscriber.

2. WCDMA adopts wider spectrumNarrowband power signals are sentout after being spread as broadband


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28 Confidential and Proprietary Information of ZTE CORPORATION

signals (spread-spectrum) withWCDMA technology.Broadband signalshave stronger anti-interference ability

than narrowband signals. Widerbandwidth realizes RAKE receiving atsubscriber end and increasescommunication quality.

Figure 5 shows WCDMA communication.Bandwidth of original signals increases

and power density decreases after

spread-spectrum. Signals meet withnoise during the transmission. Powerdensity of the noise decreases after the

dispreading, for spectrum dispreading isthe same as spectrum spreading.However, power density of original

signals is much larger than that of noise(that is, signal-to-noise ratio is high)and it is easy to resume.


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FIGURE 5 WCDMACOMMUNICATIONPRINCIPLE

F

Power

Density

F

Power

Density

F

Power

Density

F

Power

Density

(1) Original Signal(2) Signal after spread

spectrum

(3)Meeting noise during

signal transmission

(4) Signal and noise after spectrum

dispreading

Signal Noise

WCDMA adopts such advancedtechnologies as soft handover, diversity

and power control to enlarge systemcapacity and increase communicationquality greatly.

Basic Concepts of CDMA

Mobile communication systems can beclassified in multiple ways. For example,there are analog and digital by thenature of the signals; FM, PM, and AM

by the modulation mode; and FDMA,TDMA and CDMA by the multiple access

mode. CDMA (Code Division Multiple


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Access) is a new while mature wirelesstechnology developed from the spreadspectrum communication technology, a

branch of the digital technology.

Currently, the GSM mobile telephone

networks of China Unicom and ChinaMobile are built with the combination ofFDMA and TDMA. GSM has tremendousadvantages over the analog mobile

telephone system. However, its

spectrum efficiency is only three timesof the analog system. With a limitedcapacity, it has difficulty in offering

voice quality equivalent to wiredtelephone. TDMA terminals support anaccess rate of only 9.6 kbps. The TDMA

system does not support soft handover,so calls may easily be dropped, affectingthe service quality. Therefore, TDMA isnot the best technology for modern

cellular mobile communication. On theother hand, CDMA fully meets therequirements of modern mobilecommunication networks for large

capacity, high quality, and integrated

services, so it is well received byincreasingly more operators and users.

CDMA emerges from the needs forwireless communications of higherquality. In the CDMA communication

system, the signals used by differentusers for information transmission are

distinguished not by frequencies or


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timeslots, but by different codesequences. CDMA allocates one pseudorandom binary sequence for each signal

for frequency spreading, and differentsignals are allocated with differentpseudo random binary sequences. Inthe receiver, correlators are used to

separate the signals. The correlator ofeach user only receives the specifiedbinary sequences and compresses their

frequency spectrums, while ignoring allthe other signals.

The code division multiple access

concept of CDMA can be illustrated witha party of many persons. At the party,many users talk at the same time in a

room, and every conversation in theroom is in a language you do notunderstand. From your perspective, allthese conversations sound like noise. If

you know these codes, that is,relevant languages, you can ignore theconversations you do not want to hear,and focus on only these you are

interested in. The CDMA system filters

the traffic in a similar way. However,even if you understand all the languagesused, you do not necessarily hear

clearly all the conversations you areinterested in. In this case, you can tellthe speakers to speak louder, and/or

ask others to lower their voices. This issimilar to the power control in the CDMA


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system. In the frequency domain ortime domain, multiple CDMA signalsoverlap. The receiver can sort out the

signals that use the preset code patternfrom multiple CDMA signals by usingcorrelators. Other signals using differentcode patterns are not demodulated,

since their code patterns are differentfrom those generated locally at thereceiver.

One of the basic technologies of CDMAis spectrum spreading. CDMA is amultiple access technology featuring

high confidentiality. It was firstdeveloped in the Second World War toprevent interference from the enemies.

CDMA found wide application inanti-interference militarycommunications during the war. After1960s, it had been used in military

satellite communication. Later, it wasdeveloped by Qualcomm into acommercial mobile communicationtechnology.

After the first CDMA system was put

into operation for commercial purpose in1995, the technical advantages of theCDMA in theory were tested in practice,so it has seen rapid application in North

America, South America and Asia. Inmany countries and regions in theworld, including China, Hong Kong,

South Korea, Japan, and USA, CDMA is


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the major mobile communicationtechnology used. CDMA is superior toTDMA in system capacity,

anti-interference, communicationquality, and confidentiality, so IMT-2000(3G) launched by ITU and subsequentstandards all employ CDMA.

Basic Concepts of Spread SpectrumCommunication

The basic characteristic of spreadspectrum communication is that it usesa bandwidth for informationtransmission much wider than that of

the information itself. In other words,the data for transmission with certainsignal bandwidth is modulated with

high-speed pseudo random codeshaving a bandwidth wider than thesignal bandwidth. Thus, the bandwidthof the original data signals is spread,

before the signals are transmittedfollowing carrier modulation. Thereceiving end uses exactly the samepseudo random codes to process the

received bandwidth signals, convertingthe broadband signals into the originalnarrowband signals, that is,despreading, thus achieving information

communication.


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In addition, spread spectrumcommunication also has the followingcharacteristics:

1. It is a d1. igital transmission mode.

2. Bandwidth spreading is implementedby modulating the transmittedinformation with a function (spread

spectrum function) irrelevant to thetransmitted information.

3. At the receiving end, the same spreadspectrum function is used todemodulate the spread spectrumsignals, restoring the transmitted

information.

C.E. Shannon found the channel

capacity formula in his research ininformation theory, as below:

C = W Log2 (1+S/N)

Where:

C Information transmission rate

S Available signal power

W Bandwidth of the line

N Noise powerAs can be seen from the formula:

To increase C, you can either increaseW or increase S/N. In other words,when C is constant, W and S/N are

interchangeable, where the increase ofW reduces the requirement for S/N.

When the bandwidth increases to a


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certain level, the S/N is allowed tofurther decrease, making it possible forthe useful signal power to decrease to a

level close to the noise power or eveninundated in the noise. Spread spectrumcommunication uses the bandwidthtransmission technology to obtain the

benefit in S/N, which is the basic ideaand theoretical basis of spread spectrumcommunication.

Spread spectrum communication hasmany outstanding performancesinsuperable by narrowband

communication, enabling it to find wideapplication rapidly in various public andprivate communication networks. Its

advantages are outlined as below:

1. Powerful anti-interference and low biterror rate

The spread spectrum communication

system spreads the signal spectrumat the transmitting end and restoresthe original information at thereceiving end, producing spread

gains, thus greatly increasing theanti-jamming margin. Depending onthe spread spectrum gains, signalscan be extracted from noise even

when the S/N is negative. In thecurrent commercial communicationsystem, spread spectrumcommunication is the only


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communication mode that can work inthe negative S/N environment.

2. Easy same frequency use for higherradio spectrum utilization

Radio spectrum is very valuable.Although all waves from long waveand micro wave have been developed

and used, the need of the society isnot satisfied. For this reason,frequency spectrum managementauthorities were set up all over the

world. Users can only use thefrequencies granted, and divide theminto channels to avoid mutualinterference.

As spread spectrum communicationuses the correlation reception

technology, the signal transmissionpower is extremely low (


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useful signals can be extracted frommultipath signals at the receiving endwith a related technology. Also, the

same code sequence waveform frommultiple paths can be added forreinforcement, to achieve effectiveanti multipath interference.

4. Spread spectrum communication is aform of digital communication,

particularly suitable for synchronous

transmission of digital voice and data.Spread spectrum communicationoffers the encryption function for

good confidentiality, making it easy tolaunch various communicationservices.

Using multiple new technologies

including code division multipleaccess, and voice compression,spread spectrum communication ismore suitable for transmission ofcomputer network and digitized voices

and images.

5. Spread spectrum communication

involves mostly digital circuitry. Itsequipment is highly integrated, easyto install and maintain, compact, andreliable and easy to mount/expand,

and has a long MTBF.


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Transmission of Electric Waves in MobileEnvironment

The target of mobile communicationsystem is to gradually realize personalcommunication using the alwaysexistent radio channel as transmissionmedia. However, the radio channel has

poor transmission features. Firstly,there is serious and complicated fading,including path fading, shadow fading,

and multipath fading. Secondly, theradio transmission path may be direct orobstructed by mountains or buildings. Itis difficult to analyze the unknown and

unpredictable elements in radiochannels. Even the relative movingspeed may greatly affect the fading ofsignal level.

Although the features ofelectromagnetic waves change a lot

during transmission, the major changesfall into perpendicular incidence,reflection, diffraction (inflection), andscattering. In cities, there is no direct

path between transmitters and

receivers. The high buildings and largemansions cause serious diffraction loss.

Reflected by objects by many times, theelectromagnetic waves reach thereceiver through different paths. Theinteraction of these electromagnetic

waves cause multipath fading at specificplace. In a word, the strength of


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electromagnetic waves decreases withthe extension of the distance betweenthe transmitter and receiver.

Features of Land Mobile CommunicationEnvironment

1. Low Antenna of MS

Because the transmission path is

always affected by topography and

man-made environment, and the MSmoves in various topographicalenvironment and buildings, it makes

the signal received by the MS becomethe increment of a large number ofscattered and reflected signals.

2. Mobility of MS

The MS is always moving. Even theMS is not moving, the surroundingsalways change, for example, peopleand vehicles move, and wind blows

leaves. The mobility makes thetransmission path between the basestation and MS always change. In

addition, the moving direction andspeed of the MS will cause the changeof signal level.

3. Random Change of Signal Level

Varying with the time and locations,the signal level can be described bythe probability distribution in randomprocess only.


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4. Wave Guide Effect in MetropolitanEnvironment

The wave guide effect caused by thehigh buildings on both sides of thestreet make the signals received in

the direction parallel to the streetenhanced and the signals received inthe vertical direction weakened. Thereis about 10 dB difference between the

two signals. This effect is attenuated

8 km away from the base stations.

5. Loud Man-Made Noise

The man-made noise includes noise of

vehicles and electric power lines, aswell as industrial noise.

6. Strong interference

The common interferences includeco-channel interference,adjacent-channel interference,intermodulation interference, andnear-far interference.

Signal Fading in Radio Path

As the MS moves further from the basestation, the signal received becomesweaker and weaker. The reason is thatpath loss occurs to the signal. The

factors causing the path loss includecarrier frequency, transmission speed,and the topography and physiognomy

where the signal is transmitted.


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Shadow effect: The semi-dead zone inthe coverage area caused by theobstruct of high buildings and other

objects.

Near-far effect: Because the mobile

subscribers move at free will, thedistance between the subscriber and thebase station changes. If the MSs havethe same transmit power, the signal

strength at the base station is different.

If the MS is nearer to the base station,the signal received by the base stationis stronger. The non-linearity of the

communication system will beworsened, making the stronger signalstronger, the weaker signal weaker, and

the stronger signal suppress the weakersignal.

Doppler effect: The shift in frequencywhich results from the move of thesignal received at high rate. The degreeof shift is in direct ratio with the velocity

of the mobile subscriber.

Fundamentals of the WCDMA Technology

Channel Coding/Decoding

A radio channel is an adverse transmission channel. When digital

signals transmitted over a radiochannel, b i t e r ro rs may occu r in the

transmission data flow due to various


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reasons, causing image jumps anddisconnection at the receive end. Thestep of channel coding can be used to

process the data flow appropriately, sothat the system can have e r ro r

co r rec t ion capab i l i t y and an t i - i n te r fe rence capab i l i t y

Ultimately, channel coding intends toincrease the reliability of the channel,but it may reduce the transmission ofuseful information data. Channel coding

works by inserting some code elements,usually referred to as overhead, into thesource data code flow, for errordetection and correction at the receiving

end. This is like the transport of glasses.To ensure that no glasses are brokenduring this process, we usuallyuse

to

certain extent, thus greatly avoiding biterrors in the code flow. Therefore,channel coding aims at increasing data

transmission efficiency by reducing biterror rate.

f o a m s or sponge to package them.However, such packaging reduces the

total number of glasses. Similarly, overa channel with fixed bandwidth, the

total transmission code rate is fixed. Aschannel coding increases data amount,the useful information code rate isreduced. This is the cost. The number of

useful bits divided by the total numberof bits derives the coding efficiency,


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which varies slightly from one codingmode to another.

The coding/decoding technology andinterleaving technology can worktogether to increase the bit error

performance. Compared with the casewithout coding, the traditionalconvolution code can increase the biterror rate by two orders of magnitude,

to 10-3 ~ 10-4, and the Turbo code can

further increase the bit error rate to10-6. Because the Turbo code has acoding performance close to the limit of

Shannon theorem, it is adopted as thedata coding/decoding technology for 3G.The convolution code is mainly used for

voice and signaling of low data rates.

Principles of Interleaving/Deinterleaving

Interleaving/deinterleaving is animportant step of the combined channelerror correction system. The actual

errors in the channel are usually bursterrors or both burst errors and random

errors. If burst errors arefirst d isc re t i zed into random errors,

which are then corrected, the systemsanti-interference performance can beimproved. The interleaver works todiscretize long burst errors or multiple

burst errors into random errors, that is,discretizing the errors.


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The interleaving technology

rea r ranges the coded signals byfollowing certain rules. After

deinterleaving, burst errorsare d ispersed

Spread Spectrum

over time, making themsimilar to random errors that occurseparately.

Spread Spectrum is an informationtransmission mode. It modulatesinformation signals with spreading codeat sending end and enables spectrum

width of information signals much widerthan bandwidth for informationtransmission. It dispreads at receivingend with same spreading code, to

resume data of transmitted information.Figure 6 shows basic operations of

spectrumspread/dispread. Suppos ing subscriberdata rate is R, subscriber data is

101101, and according to the rule that 1is mapped as -1, 0 is mapped as +1,

map subscriber data as -1+1-1-1+1-1and time it with spreading code.

Spreading code is 01101001 in thisexample. Time each subscriber data bitto this code series including 8 codechips. Concluded data rate after spread

is 8 R and is random, like spreadingcode. Its spread spectrum factors are 8.


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Broadband signals after spreadspectrum are transmitted to receivingend via radio channels. Time code

sequence with same spread spectrumcode (dispreading code) whendispreading at receiving end to resumeoriginal subscriber data.Spreading signal speed by 8 timesfactor may result in bandwidth

spreading of subscriber data signals

(therefore, CDMA system is often calledspread spectrum system). Dispreadingresumes signal rate to original rate.FIGURE 6 SPECTRUMSPREADING/DISPREADING IN DS-CDMA

Subscriber data

= -1+1-1-1+1-1

Spread spectrum =

+1-1-1+1-1+1+1-1

Spreading signal =

Subscriber data *

Spread spectrum

Dispreading data

= Subscriber data

* Spread

spectrum

1

1

1

1

1

1

1

1

1

1

Spectrum dispreading

Spectrum spreading

Distributing different spread spectrumto different subscriber can distinguish

different subscriber, as shown in abovesector.Supposing that there are threesubscribers and that signals they sendare b1, b2 and b3, spread their signals

with spreading code of c1, c2 and c3


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and final sending signal is y=b1c1 +b2c2 + b3c3. Supposing that there is nointerference in signal transmission, the

receiving end: Gets signals after dispread with c1 z1 = y * c1 = c1 * (b1c1 + b2c2 +

b3c3) = b1 + (b2c2c1 + b3c3c1) Gets signals after dispread with c2 z2 = y * c2 = c2 * (b1c1 + b2c2 +

b3c3) = b2 + (b1c1c2 + b3c3c2) Gets signals after dispread with c3 z3 = y * c3 = c3 * (b1c1+b2c2+b3c3)

= b3 + (b1c1c3 + b2c2c3)All parts in the brackets in above three

formulas are interference of othersubscriber signals to this signal. Thisinterference can be absolutely avoided if

using orthogonalized codes.Orthogonalized code is the code that is1 after timing itself and is 0 after timingother codes. So:z1 = y * c1 = c1 * (b1c1 + b2c2 +b3c3) = b1 + (b2c2c1 + b3c3c1) = b1

+ 0 + 0 = b1z2 = y * c2 = c2 * (b1c1 + b2c2 +

b3c3) = b2 + (b1c1c2 + b3c3c2) = b2+ 0 + 0 = b2z3 = y * c3 = c3 * (b1c1 + b2c2 +b3c3) = b3 + (b1c1c3 + b2c2c3) = b3+ 0 + 0 = b3


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Modulation and Demodulation

Modulation is the process to use one

signal (know as modulation signal) tocontrol another signal of carrier (knownas carrier signal), so that acharacteristic parameter of the later

changes with the former. At thereceiving end, the process to restore theoriginal signal from the modulated

signal is called demodulation.During signal modulation, ahigh-frequency sine signal is often used

as the carrier signal. One sine signalinvolves three parameters: amplitude,frequency and phase. Modulation of

each of these three parameters isrespectively called amplitudemodulation, frequency modulation, andphase modulation.

In the WCDMA system, the modulationis Quaternary Phase Shift Keying

(QPSK). If High Speed DownlinkPackage Access (HSDPA) is used, thedownlink modulation mode can also be

16QAM.

Modulating rate of WCDMAuplinks/downlinks are both 3.84 Mcps

and modulate complex-valued code chipsequence generated by spread spectrumin QPSK mode.


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Figure 7 shows uplink modulation andFigure 8 shows downlink modulation.

FIGURE 7 UPLINK MODULATION

S

Im{S}

Re{S}

cos(t)

Complex-valuedchip sequencefrom spreadingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-shaping

FIGURE 8 DOWNLINK MODULATION

T

Im{T}

Re{T}

cos(t)

Complex-valuedchip sequencefrom summingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-

shaping

Key Technologies on WCDMA Wireless Side

Power ControlQuality Of Service (QOS) that Radio cellnetwork provides for each subscribermainly depends on

signal-to-interference ratio (SIR) ofsubscriber receiving signals. For CDMAcell system, all subscribers in same celluse same band and timeslot, and

subscribers are isolated with each other


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only by the (quasi-) orthogonalization ofspreading code. Correlationcharacteristics between each subscriber

signals are not so good and signals ofother subscribers interfere signals ofcurrent subscribers, due to multipathand delay of the radio channels.Increasing of subscribers or power ofother subscribers may enhance

interference on current subscriber.

Therefore, CDMA system is a strongpower-restricted system and strength ofinterference influences system capacity

directly.Power control is regarded as one of the

key technologies of CDMA system.Power control adjusts transmission

power of each subscriber, compensateschannel attenuation, countervailsnear-far effect and maintains allsubscribers at lowest standard of normalcommunication. It reduces interference

on other subscribers at most, increasessystem capacity and prolongs holdingtime of mobile phones.Power control is an important part in theWCDMA system. If all the MSs in a celltransmit signals at the same power, the

signals from a near MS to the BTS arestronger, and the signals from a far MSto the BTS are weaker. As a result, thestrong signals override the weak

signals. This is called Near/Far Effect in


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the mobile communication. WCDMA is aself-interference system and all usersuse the same frequency. Therefore, the

"near-far effect" is more serious. Inaddition, for the WCDMA system, thedownlink of the BTS is power restricted.To achieve acceptable call quality when

the TX power is small, both the BTS andthe MS are required to adjust powerneeded by the transmitter in real time

according to the communicationdistance and link quality. This process iscalled "power control".

Power control of WCDMA includes innerloop power control and outer loop powercontrol by effect.

Inner loop power control is used to

combat channel fade and loss, so thatthe SIR or power of the received signalscan reach the specific target value.Outer loop power control generates theSIR or power threshold for inner power

control according to the QoS in thespecific environment. By link, there isuplink power control and downlink

power control. Since the CDMA systemcapacity is mainly restricted by that ofthe uplink, uplink power control isparticularly important.

By link type, there is open loop powercontrol and closed loop power control.Open loop power control is based on the

assumption that the uplink and downlink


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channels are symmetric. It cancounteract path loss and shadow fade.Close loop power control does not need

this assumption, and it can counteractfast fade.

Open Loop Control

1. Uplink open loop control

In the WCDMA system, every MS is

calculating the path loss from the BTSto the MS all the time. When thesignal received by the MS from a BTS

is very strong, it indicates that eitherthe MS is very close to the BTS or thetransmission path is excellent. In this

case, the MS can lower the TX power,while the BTS can still receive signals

normally. On the other way around,when the signal received by the MS is

very weak, its TX power can beincreased to counteract theattenuation. Open loop power controloccurs only when the MS is powered

on and only once.

2. Downlink outer loop controlIt is the process of estimating theinitial TX power of a new requested

service. The system can estimate theinitial TX power of the downlinkchannel according to the signal qualityof the primary common pilot channel

(P-CPICH) measured by the UE. At


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the same time, the following factorshave to be taken into account: QoS,data rate, quality factor E

b/N

o,

real-time total TX power of thedownlink, interferences on this cell byother cells, and so on.

Open loop power control is simple anddirect, without needing exchange ofcontrol information between the MS

and the BTS. In addition, it features a

higher control speed and needs fewoverheads. However, in the WCDMAsystem, different frequencies are used

in uplink/downlink transmission. Thefrequency difference is far greaterthan the coherent bandwidth of

channels. Therefore, it cannot be

assumed that the fade characteristicof the downlink channel is equal tothat of the uplink channel. This is the

limitation of the open loop powercontrol.

Inner Loop Control

In this case, the receiver compares thesignal-interference ratio of the receivedsignal with the target value of the

control channel. Then, it returns atransmission power control (TPC)command to the sender. The senderdetermines whether to increase or

reduce the TX power based on the


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closed loop power control algorithmspecified by the upper layer, and makesadjustments at the specified step

according to the received command.

Outer Loop Control

Outer loop power control is asupplement to closed loop powercontrol. The working principle of uplink

outer loop power control is: Comparethe actual block error (BLER) ratio ofthe transmission channel with the targetblock error (BLER) ratio, then, slowly

adjust the target signal-interferenceratio (SIRTarget) so that the service

quality is not affected by the change ofthe radio environment, and that a

relatively constant communicationquality can be maintained.

Outer loop power control usually adjusts

the target SIR based on BLER, to makethe QoS meet the requirements. Sincedifferent services have different QoS,

there are different target SIRs.

Downlink outer loop power control issimilar to downlink inner loop powercontrol.

HandoverConcept of handover: UTRAN distributesradio resources for UE in the new cell


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because of UEs moving and systemload. Then UE synchronizes with thenew cell and transmits data each other.

Handover is a very importanttechnology in mobile communicationsystem networking.

Handover falls into:

1. Soft handover

Soft handover of cells under same

Node B (softer handover)Soft handover of cells between

different Nodes B

Soft handover of cells in same band

between different RNCs (involving Iurinterface)

2. Hard handover

Hard handover between different

operators

Hard handover in same operator

(forced hard handover)

Hard handover between systems

(such as, with GSM)

Hard handover between different modes (suchas, between FDD and TDD)

Handover refers to the redistribution ofradio resource in mobile communicationsystem in cell structure, to keep

discontinuous communication of mobilephones when moving a mobile stationfrom a district to another. Figure 9


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Handover Types in WCDMA showshandover types.FIGURE 9 HANDOVER TYPES IN WCDMA

Handover

in the mode

Handover

between modes

Handover

between systems

Soft handover (Micro diversity)

Softer handover (Among sectors)

Hard handover (Among frequencies)

Handover of FDD-TDD

UTRA FDD - GSM

R4 UTRA FDD-CDMA2000

Hard handover refers to deletingthe old link and then building a new

link. Services break off during thehandover, as shown in Figure 10.

Soft handover refers to adding a

new link (the old and the new linksexist at the same time) and deleting

the old one after stabilization.Services continue in the handover, asshown in Figure 11.


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FIGURE 10 HARD HANDOVER

Node B

Node B

Cell 1 Cell 2

FIGURE 11 SOFT HANDOVER

Node B

Node B

Cell 1 Cell 2

Softer handover refers to handoverbetween cells with same frequency

and in same base station. Differenceof soft handover and softer handoveris that combination of radio links is

realized by RNC for soft handoverwhile is realized in Node B (decidedby RNC) for softer handover.


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Inter-frequency hard handover refersto handover between cells withdifferent carriers in WCDMA.

Inter-system hard handover refers tohandover between WCDMA and other

systems (such as, GSM).

1. General flow of handover:

1) Measurement (UE)

2) Reoport on measurement results

(report from UE to RNC)

3) RNC decides whether to performhandover accpridng to the reportand algorithm (RNC sends the

command of handover to UE if it isnecessary).

Figure 12 shows detailed flow of

handover.


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FIGURE 12 HANDOVER FLOW

(A) RNC send measurement

control message to UE

(B) UE measures according to

RNC's requirement and send

measurement report message

to RNC

(C) RNC stores its measuredresults of each cell in different

carriers, for different UE

(D) Estimate signal quality of

each carrier on the report

(between bands and systems)

(E) Quality

judgment

Quality of current

carrier is good

Quality of other

systems is good

Quality of other

carriers is good

(F) Maintain

avtivated set and

monitoring set(inclduing current

and different carrier)

(G) Corresponds to

allocation resources

of virtue activatedset cell, prepared for

handover

(H) In c orresponding

cell, allocate

resources andprepared for

handover

(I) Determine the target cell and send the handover command if handover is

required

In 3GPP, events correlative to handover

are: Event correlative to soft handover in

the band: 1A ~ 1F

Measured value is usually Ec/N0 ofpilot channel, reflecting the quality of

a certain cell. 3GPP defines a series ofmeasurement events in the band. UE

reports corresponding events whenmeeting definitions.

Even t Descr ip t ion

1A

Quality of target cellimproves, entering a reportrange of relatively activating

set quality


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Event1B

Quality of target cell

decreases, depart from areport range of relativelyactivating set quality

Event

1C

The quality of a non-activatedset cell is better than that ofa certain activated set cell

Event

1D Best cell generates change

Event1E

Quality of target cellimproves, better than an

absolute threshold

Event1F

Quality of target celldecreases, worse than an

absolute threshold

Event correlative to hard handoverbetween bands: 2A ~ 2F

Ec/N0 is measured value, reflectingquality of operators by measuringcells at different bands. UE reportscorresponding events when meeting

definitions.


Event2A

Best band generates change

Event2B

Quality of currently-used bandis worse than an absolutethreshold and that of non-used

band is better than an


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absolute threshold

Event2C

Quality of non-used band isbetter than an absolute

threshold

Event2D

Quality of currently-used bandis worse than an absolute

threshold

Event2E

Quality of non-used band is

worse than an absolutethreshold

Event

2F

Quality of currently-used bandis better than an absolutethreshold

Event correlative to handover

between systems: 3A ~ 3D

RSSI is measured value for GSM. UE

reports corresponding events whenmeeting definitions.


Event3A

Quality of currently-used

UTRAN operator is worse than

an absolute threshold andquality of other radio systemsis better than an absolute

threshold

Event3B

Quality of other radio systemsis worse than an absolute

threshold

Event Quality of other radio systems


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3C is better than an absolute

thresholdEvent

3D

Best cell in other systems

generates change

For example: Adding a radio link in softhandover and Figure 13 shows signalingprocess of handover.

FIGURE 13 SOFT HANDOVER (ADDING ALINK)SIGNALING FLOW

UE Target Node B Source Node B RNC

RRC: Measurement Report(Event 1a) (From Source Node B to RNC)

NBAP: Radio Link Setup Request

NBAP: Radio Link Setup Response

Executing handover

judgement and

adding a radio link

in Target Node B

Start to receive

Distributing transmission resources on Iub interface

Start to send

RRC: Active Set Update(E1a) (From Source Node B to UE)

RRC: Active Set Update Complete (From Source & Target Node B to RNC

simutaneously)

UE connects to Source Node B and Target Node B simutaneously

2Compression mode


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UE has only one RF reception unit andcan only decode signals of onefrequency at one time. Therefore,

compression mode is necessary ifmeasuring two cells of different bandsor I different cells. Figure 14 showscompression mode priciple.

FIGURE 14 COMPRESSION MODEPRINCIPLE

In compression mode, Node Bcompresses data when sending somedownlink channel frames. UE takesadvantage of remaining time for

measurement of different bands.Compression mode can be realized bydrilling and halving spreading factors,and so on. When measuring between

frequencies, the system negotiates withUE whther to support and select

compression mode.


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RAKE Receiver

Since multipath signals contain useful

information, CDMA receivers improvethe S/N of the received signals bycombining multipath signals. What aRAKE receiver does is to receive the

various channels of signals frommultipath signals through multiplerelated detectors, and then combine

them. The RAKE receiver is a classicaldiversity receiver specially designed forthe CDMA system. Its theoretical basisis that when the propagation delay

exceeds one chip code cycle, multipathsignals are actually seen to be mutuallyirrelevant.

RAKE reception separates and combinesmultipath signals. Different from theIS-95 A, WCDMA has three times of

multipath resolving power. In addition,in a WCDMA system, the pilotinformation sent by the user can beused for coherent combination on the

reverse link. The theoretical analysis of

WCDMA shows that if the reverse linkuses 8-path RAKE reception, over 75%signal energies are used. The

suppression of the RAKE reception formultiple access interference depends onthe correlation between the different

user characteristic codes.


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Code Resource Allocation

In WCDMA, code resources fall into

channelization codes, scrambling codesand synchronization codes.

In mobile communication

system, primary scrambling codes are

to differentiate cells, channelizationcodes are to differ physical channels on

the downlink, and scrambling codes areto differentiate users on the uplink.Orthogonal Variable Spreading Factor(OVSF) is precious ans scarce resource,so one cell corresponds to one code

table. To access more users and toincrease system capacity, make use ofcode resources reasonably. It is very

important to plan and manage downlinkchannelization code resources.

Although there are many scrambling

codes on the uplink, it is necessary toplan scrambling of RNC, to avoiddifferent users in different RNC usesame scrambling codes.

Channelization Code

1. Brief introduction

Channelization codes are based onOVSF technology, which can change

the spreading factor and ensureorthogonality between different


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spreading codes of different length.On the downlink, channelization codesare to differentiate transmission from

the same source, that is, downlinkswithin a sector, while on the uplink, todifferentiate dedicated physicalchannels of all uplinks from a UE

(including dedicated physical datachannel and dedicated physicalcontrol channel).

2. Gene

Basic Technology of WCDMA

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