Wcdma p&o b en Radio Theory 1 31

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WCDMA Radio Theory


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Contents

1 WCDMA system overview .................................................................................................................................2

1.1 WCDMA Technical Standards Development Trends ....................................................................................2

1.1.1 Overview ...................................................................................................................................2

1.1.2 3GPP Standard Development Status ........................................................................................4

1.1.3 Analysis on 3GPP standard Version Evolution ........................................................................7

1.1.4 Analysis on Evolution of 3GPP Technologies ..........................................................................8

1.2 IMT2000 Frequency Band Allocation .........................................................................................................14

1.3 Composition of WCDMA System ..............................................................................................................15

1.3.1 UE (User Equipment ) ............................................................................................................15

1.3.2 UTRAN (UMTS Terrestrial Radio Access Network ) ...........................................................16

1.3.3 CN (Core Network) ................................................................................................................17

2 WCDMA Basic Technology .............................................................................................................................19

2.1 Concept of WCDMA Realizing Broadband Communication .....................................................................19

2.1.1 Basic Concepts of CDMA ......................................................................................................20

2.1.2 Basic Concepts of Spread Spectrum Communication ...........................................................22

2.2 Transmission of Electric Waves in Mobile Environment ...........................................................................24

2.2.1 Features of Land Mobile Communication Environment .......................................................24

2.2.2 Signal Fading in Radio Path ...................................................................................................25

2.3 Fundamentals of the WCDMA Technology ................................................................................................26

2.3.1 Channel Coding/Decoding .....................................................................................................26

2.3.2 Principles of Interleaving/Deinterleaving ..............................................................................26

2.3.3 Spread Spectrum .....................................................................................................................27

2.3.4 Modulation and Demodulation ...............................................................................................28

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1 WCDMA system overview

1.1 WCDMA Technical Standards Development Trends

1.1.1 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 following disadvantages: limited frequency spectrum

resources, low frequency spectrum utilization, and weak 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 low

system capacity, hardly meeting the demand for high-speed bandwidth services and

impossible for the system to implement global roaming. Therefore, the 3G 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 technology opens the door to a brand new mobile communication world. It

brings more fun to the people. In addition to clearer voice services, it allows users toconduct multimedia communications with their personal mobile terminals, for example,

Internet browsing, multimedia database access, real-time stock quotes query, videophone,

mobile e-commerce, interactive games, wireless personal audio player, video transmission,

knowledge acquisition, and entertainments. What more unique are location related

services, which allow users to know about their surroundings at anytime anywhere, for

example, block map, locations of hotels and super markets, and weather forecast. The 3G

mobile phone is bound to become a good assistant to peoples life and work.

The 3G mobile communication aims at meeting the future demand for mobile usercapacity and providing mobile data and multimedia communication services.

Initially, mobile communication technologies were developed separately, as various

countries and technical 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 EU has

GSM. On one hand, this situation helped to meet the needs of the users at the early stage

of mobile communication and expand the mobile communication market. On another

hand, it created barriers between the regions, and made it necessary to unify the mobile

communication systems globally. Under such a context, ITU launched the standardization

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of the 3G mobile communication system in 1985.

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

generation communication system proposed by ITU in 1985, when it was actually referred

to as Future Public Land Mobile Telecommunications System (FPLMTS). In 1996, it was

officially renamed to IMT-2000. In addition, the 3G mobile communication technology

extends the integrated bandwidth network service as far as it can to the mobile

environment, transmitting multimedia information including high quality images at rates

up to 10 Mbps.

Compared with the existing 2G system, the 3G system has the following characteristics as

summarized below:

1. Support for multimedia services, especially Internet services

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 WCDMA work in the FDD

mode, while TD-SCDMA works in the TDD mode, where the uplink and downlink of the

system work in different timeslots of the same frequency.

The 3G mobile communication is designed to provide diversified and high-quality

multimedia services. To achieve 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 the uplink and downlink

In the concept evaluation of the 3G mobile communication specification proposals, the

WCDMA technology is adopted as one of the mainstream 3G technologies thanks to its

own technical advantages.

WCDMA was originated by standardization organizations and manufacturers in European

countries and Japan. WCDMA inherits the high standardization and openness of GSM, and

its standardization progresses smoothly. WCDMA is the third generation mobile


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communication standard developed by 3GPP, with the GSM MAP as its core and UTRAN

(UMTS Terrestrial Radio Access Network) as its wireless interface. Using the chip rate of

3.84 Mbps, it provides data transmission rate up to 14.4Mbps within 5MHz bandwidth.

The WCDMA technology has the following characteristics:

Supporting both asynchronous and synchronous BTSs, for easy and flexible

networking

Using QPSK modulation mode (the HSDPA services also use the 16QAM modulation

mode)

Using pilot assisted coherent demodulation

Accommodating transmission of multiple rates, and implementing multi-rate and

multimedia services by changing the spread spectrum ratio and using multi-mode

concurrent transmission

Rapid and efficient power control of uplink/downlink greatly reduces multiple access

interference of the system, but increases the system capacity while reducing the

transmission power.

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

compatibility with the GSM/GPRS network.

Supporting soft handover and softer handover, with three handover modes, inter-

sector soft handover, inter-cell soft handover, and inter-carrier hard handover

1.1.2 3GPP Standard Development Status

3GPP standard versions include R99, R4, R5, R6 and R7.

R99 version was frozen formally in Mar, 2000, and refreshes once every three months.

Current commercial version of R99 is based on the version of June, 2001, for in later

version, the number of CR is decreasing 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 versions that providers

support are the version of June, 2004. R6 version was frozen in June, 2005 and may be

stable 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

developing status.

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1.1.2.1 Basic Network Structure Based on R99

Figure 1.2-1 Basic Network Structure of R99

The R99 is the first phase version of 3GPP in 3G network standardization. The R99 was

already frozen in June 2001, and subsequent revision is made on the R4. The basic

configuration structure of the R99 is illustrated in Figure 1.2-1. To guarantee the

investment interests of telecom operators, the network structure of the R99 is designed

with 2G/3G compatibility fully in mind, for smooth evolution to 3G. Therefore, the core

network in the basic network structure remains unchanged. To support 3G services, some

NEs are added with appropriate interface protocols, and the original interface protocols are


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also improved by different degrees.

1.1.2.2 Network Structure Based on UMTS R4

Same as the R99 network, the basic structure of the R4 network consists of the corenetwork and wireless access network, and there are the CS domain and PS domain on the

core network side. The basic NE entities and the interfaces are largely inherited from the

definitions of entities and interfaces of the R99 network. The network entities with the

same definitions as the R99 network remain unchanged in basic functionality, and the

related protocols are also similar.

Compared with the R99, the R4 network structure has tremendous changes in the structure

of the CS domain of the core network, while those of the PS domain of the core network

and of the UTRAN also remain the same.

According to the idea of separation between call control, bearer and bearer control, the

network entity (G) MSC of the CS domain of the R99 network evolves to the MGW and

(G) MSCServer in the R4 stage, with R-SGW and T-SGW added. In addition, related

interfaces are also changed, with the Mc interface added between the MGW and MSC

Sever, the Nc interface between the MSC Sever and GMSC Sever, and the Nb interface

between MGWs, and the Mh interface between the MR-MGW and HLR.

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Figure 1.2-2 Basic Network Structure of the R4

B S S

B S C

R N S

R N C

C N

N o d e N o d e

I u P S

I u r

I u b

U S I M

M E

M S

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M S C s e r S G S N

G s

G G S Ns e r v e r

G nH S S ( H L R )

G r

G cC

D

N c

H

E I R

F G f

G iP S T N

I u C S

V L R

B

G p

V L R

G

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U m

R N C

A b i

S I M

S I M- M E i o r

M S C s e r B

P S T N

c e l l

C S-M G WC S-M G W

-

M G

A u C

T-S G W R-S G

M cM c

N b

P S T P S T N

N c

M c

M h

A G b

E

1.1.3 Analysis on 3GPP standard Version Evolution

During the evolution from GSM/GPRS to 3GPP R99, brand UTRAN introduced includes

such key technologies as WCDMA, power control, multipath Rake receiver. In addition,

four QoS service types are put 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 the introduction of UTRAN CN furthest. Most representative features of R4

from R99: Separation of CS domain control layer and transmission layer, convergence of


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transmission resources in CS and PS domains, and increase of resource transmission

efficiency.

UTRAN in R4 version does not have substantive evolution and only performs some

optimizations.

During the evolution from R4 to R5, IP multimedia subsystem is introduced into CN and

the interface connecting GERAN is added. There is great change in UTRAN: IP

transmission technology and HSDPA are introduced, which makes peak rate of the cell up

to about 10 Mbps, much greater than the peak bandwidth that R4 and R99 versions can

support (in the field, WCDMA supporting HSDPA is called 3.5 G). R5 also supports Iu

Flexible, allowing a RNC to access several MSCs or SGSNs simultaneously, which saves

investment on access network resources for operators.

intercommunication of WLAN and UMTS. UTRAN evolution 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 UTMS with other networks (such as, VLAN) and

enhanced MBMS will be increased.

1.1.4 Analysis on Evolution of 3GPP Technologies1.1.4.1 Evolution of CN Technology

Total IP CN

Brand UTRAN is introduced in initial phase of 3GPP R99, 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 and transmission layer, realizes voice packet and signaling packet, transmits CS and

PS domains application in CN based on one IP.

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

IMS adopts Session Initiation Protocol (SIP) that IETF defines and provides IP services

that Qos is sensitive to (such as, VoIP) in packet switching domain, to intercommunicate

fixed IP terminal and 3G mobile terminal.

In R6 version, functions of IMS are enhanced greatly, including the intercommunication of

local IP multimedia network and other IP multimedia networks, intercommunication of

IMS and CS, intercommunication of IMS based on IPV4 and IPV6, multi-party conference

service, IMS group management and SIP appended to IMS. As a result, wider and more

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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 mobile network.

Network sharing

In 3GPP R99/R4, one RNC can only connect one MSC or SGSN, resulting in low

utilization ratio of resources.

In R5, Iu-Flex is introduced between CN and UTRAN, realizing the UTRAN resources

sharing among several nodes of one operator. It saves the cost on UTRAN and

substantially develops the network sharing technology.

In R6, network sharing function is expanded continuously, which provides the

configuration mode 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 amalgamation of UMTS and WLAN are fulfilled

(Phase I), which is strengthened in R7 plans (Phase II). In addition, in R7, defines

feasibility of total IP network operation. Intercommunication and amalgamation of CN

with other networks is future development trend.

1.1.4.2 Evolution of Radio Access Network Technologies

High-speed broadband access

Compared with GSM/GPSR RAN, R99 introduced new UTRAN. UTRAN is based on

WCDMA radio interface 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.

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

increases spectrum utilization ratio. Cell downlink peak rate reaches 14 Mbps. In the field,

the system supporting HSDPA is defaulted as 3.5 G system.

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

In R7 version, Multiple Input Multiple Output (MIMO) antenna technology is introduces,

which enables several transmitting and receiving antennas to send and receive signals in

same band. As a result, system capacity and spectrum utilization ratio is increased in

germination. MIMO antenna technology meets the requirements for high speed services in


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future mobile communication 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 may develop as the core technology base of 3G advanced system

(such as, Beyond 3G, 3.9G and E3G). With continuous development of 3GPP

standardization, OFDM will be applied to broadband mobile communication field more

widely in the near future.

In the future, MIMO and OFDM technologies will combine. System test results improve

that MIMO-OFDM system which has two transmission antennas and two receiving

antennas can provide the data transmission rate from score to a hundred million.

In a word, evolution process of radio access network on access bandwidth is: 2 Mbps

(R99) HSDPA DL 14 Mbps (R5) HSDPA DL 14 Mbps/HSUPA UL 5.7 Mbps (R6)

--> MIMO (R7) OFDM (LTE). Its evolution is to introduce all kinds of technologies,

increasing spectrum utilization ratio furthest and meeting the requirements for high speed

data transmission.

Mobile management

From R99 version, WCDMA has differences from GSM/GPRS in mobile management,

including soft handover, Iur interface, re-positioning, handover and reselection between

2/3G. From R4 version, Iur interface has introduced such flows as public measurement

and radio link congestion, which makes radio resource management and load control of Iur

interface be organic part of UTRAN. At the same time, migration or compatibility criteria

with GERAN are under way, including Iur-g, cell change that network aids.

IP transmission

UTRAN in R99/R4 versions adopts TDM and ATM. CN in R4 version successfully

introduces the base of IP transmission technology.

3GPP UTRAN in R5 version also introduces IP transmission technology. IP transmission

is a selective technology of UTRAN and it makes UTRAN transmit based on IP coreswitching network. As a result, flexibility of transmission networking is increased and

construction cost of operators is reduced. IP transmission is also UTRAN transmission

development trend.

In transmission, R4/R5 versions added transmission bearer modification and

reconfiguration, to further optimize the performance of transmission bearer.

Antenna technology

During the evolution of 3GPP standards, 3GPP also has evolution in antenna technology

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and antenna evolution process is: Two projects of wave cluster figuration (R5) Fixed

wave cluster figuration project and 3GPP electronic modulation antenna (R6) MIMO

(R7).

The evolution is to improve link performance of the system by introducing all kinds of

antenna technologies, increasing system capacity.

In R5 version, radio wave cluster figuration technology is introduced to increase system

link performance and capacity. Two projects are put forward: fixed wave cluster figuration

and user special wave cluster figuration. In R6 version, user special 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

modulate antennas of BS system. Most operators purchase antennas from third party. In

these years, Antenna Interface Standard Group (AISG) has put forward AISG interface

standards. However, since 3GPP does not definite antenna interfaces in R99/R4/R5 phases,

it is difficulty for manufacturers to have same antenna interface, antenna type and network

optimization. Therefore, in R6 version, 3GPP uniforms interface of RET and introduces

Iuant antenna interfaces. Standardization of RET interfaces makes remote network

optimization possible on condition that several manufacturers provide antennas.

In R7 version, 3GPP puts forward MIMO, which increases system capacity and spectrum

utilization ratio in germinations. Although MIMO is not mature at present, it is a great

breakthrough of antenna technology in mobile communication field and also a developing

direction of future intelligent antenna technology.

Positioning technology

In R99 version, UE positioning technology based on cell ID is introduced. It is a rough

positioning technology. In R99 version, frames of OTDOA and A-GPS are introduced, too.

In R4 version, criteria of Iub/Iur interfaces are put forward, which improves OTDOA and

A-GPS positioning technologies.

In R5 version, criteria of SMLC-SRNC interfaces are put forward and they are open to

support A-GPS positioning technology (not supporting other positioning technologies).

In R4 and R5, lowest performance requirements for A-GPS measurement are not given.

Therefore, in R6 version, positioning precision of A-GPS is defined (positioning range of a

mobile station is 30 to 100 m and response time is 2 to 20 s. In R6 version, SMLC-SRNC

interfaces are open to support three positioning technologies (CellID, OTDOA and A-

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In R7 version, Uplink-Time Difference Of Arrival (U-TDOA) is put forward. It is hoped to

provide solutions that are more flexible and whose positioning precision is higher.

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. All positioning technologies can be supplements to each other during

the application.

1.1.4.3 Evolution of UMTS QoS Technology

With the close combination of radio communication technology and IP technology, mobile

communication network develops from circuit switching network of GSM to packet

switching network of GSM, and to 3G, 3.5G and UMTS that provide high speed real-time

data services. During the whole evolution of mobile network, QoS technology develops to

mature to provide satisfactory services according to features of different services. Analysis

on QoS in GSM, GPRS, R99, R4, R5, R6 and R7 tell development of mobile network

QoS.

GSM is based on circuit switching mode. It is simple. Connection of circuit can ensure

QoS. GSM defines a series 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 no Connection concept in GPRS, so

QoS assurance of GPRS is more complicated than that of GSM. QoS parameters 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.

QoS of UMTS is to provide end-to-end assurance of services, which is introduced in R99

version, as shown in Figure 1.2-3. End-to-end QoS covers all NEs, including user

terminal, access network entity and CN entity. Processing of different interface QoS

parameters must be same. The introduction of QoS layered architecture is a large

advancement during the QoS evolution.

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Figure 1.2-3 QoS Frame of UMTS

TE CN

Gateway

MT UTRAN CN Iu

EDGE

NO DE

TE

End-to-End Service

TE/MT Local

Bearer ServiceUMTS B earer Service

External

Bearer Service

Radio Access Bearer ServiceCN Bearer

Service

RadioBearer Service

IuBearer Service

BackboneBearer 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 ATM bearing modes (in R4 and later version, transmission and control in circuit

domain is separated and IP transmission is selective). Its packet domain supports IP bearer.

TDM and ATM bearers both provide QoS assurance. IP bearer of CN adopts the QoS

technology that IETF defines, including integrated service/resource preservation

(IntServ/RSVP), Multiple Protocol Label Switching (MPLS), Differential Service

(DiffServ), flow project and constraint-based path seek, and so on.

In R99 version, four QoS types are introduced: Conversational, data streaming, interactive

and background. It also defines QoS parameters more than GSM and GPRS. There are

new requirements for transmission delay, retransmission mechanism, jitter and code error

rate of above four types.

In R4 version, QoS that AAL2 connects on Iub and Iur is optimized, to improve real-time

services support. In addition, QoS negotiation mechanism of radio access bearer is

introduced to make use of radio resources more effectively and to enhance the construction

capability of radio access bearer.

In R5 version, intercommunication and combination of 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 with outer IP network. IMS, which is


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QoS policy control mechanism based on services, is also introduced in R5 version.

In R6 version, QoS policy control mechanism based on services is evolved as an

independent functional entity, providing services in all packet domains with QoS policy

control mechanism based on services. This mechanism 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 intelligent management of QoS.

In R7 version, compatibility or migration of UTMS and WLAN is put forward. Uniform IP

QoS is what future UMTS QoS technology will develop to.

Evolution process of QoS is: QoS parameters do not transmit in the network (GSM)

QoS parameters transmit between UE and SGSN/GGSN Number of QoS parameters

increase (GPRS) QoS layered architecture, 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 access bearer (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

UMTS and WLAN (R7 and later version).

1.2 IMT2000 Frequency Band Allocation

In 1992, World Radio-communication Conference (WRC-92) allocated the frequency

bands for the 3G mobile communication, with a total bandwidth of 230 MHz, as shown in

Figure 1.3-4

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Figure 1.3-4 Frequency Spectrum Allocation of 3G Mobile Communication

At WRC92, ITU planned the symmetric frequency spectrum resources of 120MHz

(1920MHz ~ 1980MHz, 2110MHz ~ 2170MHz) for use by the FDD, and asymmetric

frequency spectrum resources of 35MHz (1900MHz ~ 1920MHz, 2010MHz ~ 2025MHz)

for use by the TDD.

At WRC2000, the 800 MHz band (806MHz ~ 960MHz), 1.7GHz band (1710MHz ~

1885MHz), and 2.5GHz band (2500MHz ~ 2690MHz) were added for use by the IMT-

2000 services. These two combination make the future spectrum for 3G reach over 500

MHz, reserving enormous resource space for future applications.

1.3 Composition of WCDMA System

The Universal Mobile Telecommunication System (UMTS) is a 3G mobile

communication system adopting WCDMA air interface. Therefore, the UMTS is usually

called a WCDMA system.

In terms of functions, the network units comprise the Radio Access Network (RAN) and

Core Network (CN). The RAN accomplishes all the functions related to radio

communication. The CN handles the exchange and routing of all the calls and data

connections within the UMTS with external networks. The RAN, CN, and the User

Equipment (UE) together constitute the whole UMTS.

1.3.1 UE (User Equipment )

The UE is an equipment which can be vehicle installed or hand portable. Through the Uu


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interface, the UE exchanges data with network equipment and provides various CS

domain and PS domain services, including common voice services, broadband voice

services, mobile multimedia services, and Internet applications (such as E-mail, WWW

browse, and FTP).

1.3.2 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 the WCDMA system, the Node B is composed

of the wireless transceiver and baseband processing part. Connected with the RNC through

standard Iub interface, Node B processes the Un interface physical layer protocols. It

provides the functions of spectrum spreading/despreading, modulation/demodulation,

channel coding/decoding, and mutual conversion between baseband signals and radio

signaling.

2) RNC

The RNC manages various interfaces, establishes and releases connections, performs

handoff and macro diversity/combination, and manages and controls radio resources. It

connects with the MSC and SGSN through lu interface. The protocol between UE and

UTRAN is terminated here.

The RNC that controls Node B is called Controlling RNC (CRNC). The CRNC performs

load control and congestion control of the cells it serves, and implements admission

control and code word allocation for the wireless connections to be established.

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

the related RNC has two independent logical functions:

Serving RNC (SRNC). The SRNC terminates the transmission of subscriber data and theIu connection of RANAP signaling to/from the CN. It also terminates the radio resource

controlling signaling (that is the signaling protocol between UE and UTRAN). In addition,

the SRNC performs L2 processing of the data sent to/from the radio interface and

implements some basic operations related to radio resources management.

Drift RNC (DRNC) All the other RNCs except the SRNC are DRNCs. They controls the

cells used by the UEs.

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1.3.3 CN (Core Network)

The CN is in charge of the connections with other networks as well as the management

and communication with UEs. The CN can be divided into CS domain and PS domain

from the aspect of logic.

The CS domain equipment refers to the entities that provide circuit connection or related

signaling connection 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 to subscribers. 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 location register (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 the WCDMA core network, the MSC/VLR

connects with the UTRAN through Iu CS interface, with external networks (PSTN, ISDN,

and other PLMNs) through PSTN/ISDN interface, with the HLR/AUC through C/D

interface, with the MSC/VLR, GMSC or SMC through E interface, with the SCP through

CAP interface, and with the SGSN through Gs interface.

The MSC/VLR accomplishes call connection, mobility management, authentication, and

encryption in the CS domain.

2) GMSC

As the gateway node between the CS domain of WCDMA network and external networks,

the GMSC is an optional entity. It connects with the external networks (PSTN, ISDN, and

other PLMNs) through PSTN/ISDN interface, with the HLR through C interface, and with

the SCP through CAP interface.


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WCDMA Radio Theory

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

3) SGSN

As the functional node in the PS domain of WCDMA core network, the SGSN connectswith the UTRAN through Iu_PS interface, with GGSN through Gn/Gp interface, with the

HLR/AUC through Gr interface, with the MSC/VLR through Gs interface, with the SCP

through CAP interface, with the SMC through Gd 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 packets between the WCDMA network and external

data networks, and encapsulates these data packets. The major function of the GGSN is to

provide the interface to the external IP packet-based network, thus the UEs can access the

gateway of the external packet-based network. To the external networks, the GGSN seems

like the IP router that can be used to address all the mobile subscribers in the WCDMA

network. It exchanges routing information with external networks.

5) HLR

The HLR connects with the VMSC/VLR or GMSC through C interface, with the SGSN

through Gr interface, 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 Radio Theory

2 WCDMA Basic Technology

2.1 Concept of WCDMA Realizing Broadband Communication

WCDMA (Wideband CDMA) is CDMA radio communication mode cased on direct

spread-spectrum technology. WCDMA has an obvious advantage over GSM and IS-95 in

subscriber capacity and radio transmission performance, for it adopts a series of key

technologies.

WCDMA bears following two meanings literally:

1. WCDMA adopts CDMA communication technology1.

CDMA technology is the most advanced communication technology in the world at

present. It takes advantage of different codes to divide different channel and then

distinguish different subscriber.

2. WCDMA adopts wider spectrum

Narrowband power signals are sent out after being spread as broadband signals (spread-

spectrum) with WCDMA technology. Broadband signals have stronger anti-interferenceability than narrowband signals. Wider bandwidth realizes RAKE receiving at subscriber

end and increases communication quality.

Figure 2.1-5 shows WCDMA communication. Bandwidth of original signals increases and

power density decreases after spread-spectrum. Signals meet with noise during the

transmission. Power density of the noise decreases after the dispreading, for spectrum

dispreading is the 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 2.1-5 WCDMA Communication Principle

F

PowerDensity

F

PowerDensity

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 advanced technologies as soft handover, diversity and power

control to enlarge system capacity and increase communication quality greatly.

2.1.1 Basic Concepts of CDMA

Mobile communication systems can be classified in multiple ways. For example, there are

analog and digital by the nature 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 Access) is a new while mature wireless technology developed from the spread

spectrum communication technology, a branch of the digital technology.

Currently, the GSM mobile telephone networks of China Unicom and China Mobile are

built with the combination of FDMA and TDMA. GSM has tremendous advantages over

the analog mobile telephone system. However, its spectrum efficiency is only three times

of the analog system. With a limited capacity, it has difficulty in offering voice quality

equivalent to wired telephone. TDMA terminals support an access rate of only 9.6 kbps.

The TDMA system does not support soft handover, so calls may easily be dropped,

affecting the service quality. Therefore, TDMA is not the best technology for modern

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WCDMA Radio Theory

cellular mobile communication. On the other hand, CDMA fully meets the requirements of

modern mobile communication networks for large capacity, high quality, and integrated

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

CDMA emerges from the needs for wireless communications of higher quality. In the

CDMA communication system, the signals used by different users for information

transmission are distinguished not by frequencies or timeslots, but by different code

sequences. CDMA allocates one pseudo random binary sequence for each signal for

frequency spreading, and different signals are allocated with different pseudo random

binary sequences. In the receiver, correlators are used to separate the signals. The

correlator of each user only receives the specified binary sequences and compresses their

frequency spectrums, while ignoring all the other signals.

The code division multiple access concept of CDMA can be illustrated with a party of

many persons. At the party, many users talk at the same time in a room, and every

conversation in the room is in a language you do not understand. From your perspective,

all these conversations sound like noise. If you know these codes, that is, relevant

languages, you can ignore the conversations 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 languages used, you do not necessarily hear clearly all the

conversations you are interested in. In this case, you can tell the speakers to speak louder,

and/or ask others to lower their voices. This is similar to the power control in the CDMA

system. In the frequency domain or time domain, multiple CDMA signals overlap. The

receiver can sort out the signals that use the preset code pattern from multiple CDMA

signals by using correlators. Other signals using different code patterns are not

demodulated, since their code patterns are different from those generated locally at the

receiver.

One of the basic technologies of CDMA is spectrum spreading. CDMA is a multiple

access technology featuring high confidentiality. It was first developed at the time of

Second World War to prevent interference from the enemies. CDMA found wide

application in anti-interference military communications during the war. After 1960s, it

had been used in military satellite communication. Later, it was developed by Qualcomm

into a commercial mobile communication technology.

After the first CDMA system was put into operation for commercial purpose in 1995, the

technical advantages of the CDMA in theory were tested in practice, so it has seen rapid

application in North America, South America and Asia. In many countries and regions in

the world, including China, Hong Kong, South Korea, Japan, and USA, CDMA is the


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major mobile communication technology used. CDMA is superior to TDMA in system

capacity, anti-interference, communication quality, and confidentiality, so IMT-2000 (3G)

launched by ITU and subsequent standards all employ CDMA.

2.1.2 Basic Concepts of Spread Spectrum Communication

The basic characteristic of spread spectrum communication is that it uses a bandwidth for

information transmission much wider than that of the information itself. In other words,

the data for transmission with certain signal bandwidth is modulated with high-speed

pseudo random codes having a bandwidth wider than the signal bandwidth. Thus, the

bandwidth of the original data signals is spread, before the signals are transmitted

following carrier modulation. The receiving end uses exactly the same pseudo random

codes to process the received bandwidth signals, converting the broadband signals into the

original narrowband signals, that is, despreading, thus achieving information

communication.

In addition, spread spectrum communication also has the following characteristics:

1. It is a digital transmission mode.

2. Bandwidth spreading is implemented by modulating the transmitted information with

a function (spread spectrum function) irrelevant to the transmitted information.

3. At the receiving end, the same spread spectrum function is used to demodulate the

spread spectrum signals, restoring the transmitted information.

C.E. Shannon found the channel capacity formula in his research in information 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 power

As can be seen from the formula:

To increase C, you can either increase W or increase S/N. In other words,

when C is constant, W and S/N are interchangeable, where the increase of

W reduces the requirement for S/N. When the bandwidth increases to a

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WCDMA Radio Theory

certain level, the S/N is allowed to further decrease, making it possible for

the useful signal power to decrease to a level close to the noise power or

even inundated in the noise. Spread spectrum communication uses the

bandwidth transmission technology to obtain the benefit in S/N, which is

the basic idea and theoretical basis of spread spectrum communication.

Spread spectrum communication has many outstanding performances

insuperable by narrowband communication, enabling it to find wide

application rapidly in various public and private communication networks.

Its advantages are outlined as below:

1. Powerful anti-interference and low bit error rate

The spread spectrum communication system spreads the signal spectrum at the

transmitting end and restores the original information at the receiving end, producing

spread gains, thus greatly increasing the anti-jamming margin. Depending on the spread

spectrum gains, signals can be extracted from noise even when the S/N is negative. In the

current commercial communication system, spread spectrum communication is the only

communication mode that can work in the negative S/N environment.

2. Easy same frequency use for higher radio spectrum utilization

Radio spectrum is very valuable. Although all waves from long wave and micro wave

have been developed and used, the need of the society is not satisfied. For this reason,

frequency spectrum management authorities were set up all over the world. Users can only

use the frequencies granted, and divide them into channels to avoid mutual interference.

As spread spectrum communication uses the correlation reception technology, the signal

transmission power is extremely low (


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communication offers the encryption function for good confidentiality, making it easy to

launch various communication services.

Using multiple new technologies including code division multiple access, and voice

compression, spread spectrum communication is more suitable for transmission of

computer network and digitized voices and images.

5. Spread spectrum communication involves mostly digital circuitry. Its equipment is

highly integrated, easy to install and maintain, compact, and reliable and easy to

mount/expand, and has a long MTBF.

2.2 Transmission of Electric Waves in Mobile Environment

The target of mobile communication system is to gradually realize personal

communication using the always existent radio channel as transmission media. However,

the radio channel has poor transmission features. Firstly, there is serious and complicated

fading, including path fading, shadow fading, and multipath fading. Secondly, the radio

transmission path may be direct or obstructed by mountains or buildings. It is difficult to

analyze the unknown and unpredictable elements in radio channels. Even the relative

moving speed may greatly affect the fading of signal level.

Although the features of electromagnetic waves change a lot during transmission, themajor changes fall into perpendicular incidence, reflection, diffraction (inflection), and

scattering. In cities, there is no direct path between transmitters and receivers. The high

buildings and large mansions cause serious diffraction loss. Reflected by objects by many

times, the electromagnetic waves reach the receiver through different paths. The

interaction of these electromagnetic waves cause multipath fading at specific place. In a

word, the strength of electromagnetic waves decreases with the extension of the distance

between the transmitter and receiver.

2.2.1 Features of Land Mobile Communication Environment

1. Low Antenna of MS

Because the transmission path is always affected by topography and man-made

environment, and the MS moves in various topographical environment and buildings, it

makes the signal received by the MS become the increment of a large number of scattered

and reflected signals.

2. Mobility of MS

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WCDMA Radio Theory

The MS is always moving. Even the MS is not moving, the surroundings always change,

for example, people and vehicles move, and wind blows leaves. The mobility makes the

transmission path between the base station and MS always change. In addition, the moving

direction and speed of the MS will cause the change of signal level.

3. Random Change of Signal Level

Varying with the time and locations, the signal level can be described by the probability

distribution in random process only.

4. Wave Guide Effect in Metropolitan Environment

The wave guide effect caused by the high buildings on both sides of the street make the

signals received in the direction parallel to the street enhanced and the signals received in

the vertical direction weakened. There is 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, as well as

industrial noise.

6. Strong interference

The common interferences include co-channel interference, adjacent-channel interference,

intermodulation interference, and near-far interference.

2.2.2 Signal Fading in Radio Path

As the MS moves further from the base station, the signal received becomes weaker and

weaker. The reason is that path loss occurs to the signal. The factors causing the path loss

include carrier frequency, transmission speed, and the topography and physiognomy where

the signal is transmitted.

Shadow effect: The semi-dead zone in the coverage area caused by the obstruct of high

buildings and other objects.

Near-far effect: Because the mobile subscribers move at free will, the distance between the

subscriber and the base station changes. If the MSs have the 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 station is stronger. The non-linearity of the communication

system will be worsened, making the stronger signal stronger, the weaker signal weaker,

and the stronger signal suppress the weaker signal.

Doppler effect: The shift in frequency which results from the move of the signal received


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at high rate. The degree of shift is in direct ratio with the velocity of the mobile subscriber.

2.3 Fundamentals of the WCDMA Technology

2.3.1 Channel Coding/Decoding

A radio channel is an adverse transmission channel. When digital signals transmitted over

a radio channel, bit errors may occur in the transmission data flow due to various reasons,

causing image jumps and disconnection at the receive end. The step of channel coding can

be used to process the data flow appropriately, so that the system can have error correction

capability and anti-interference capability to certain extent, thus greatly avoiding bit errors

in the code flow. Therefore, channel coding aims at increasing data transmission efficiencyby reducing bit error rate.

Ultimately, channel coding intends to increase the reliability of the channel, but it may

reduce the transmission of useful information data. Channel coding works by inserting

some code elements, usually referred to as overhead, into the source data code flow, for

error detection and correction at the receiving end. This is like the transport of glasses. To

ensure that no glasses are broken during this process, we usually use foams or sponge to

package them. However, such packaging reduces the total number of glasses. Similarly,

over a channel with fixed bandwidth, the total transmission code rate is fixed. As channelcoding increases data amount, the useful information code rate is reduced. This is the cost.

The number of useful bits divided by the total number of bits derives the coding efficiency,

which varies slightly from one coding mode to another.

The coding/decoding technology and interleaving technology can work together to

increase the bit error performance. Compared with the case without coding, the traditional

convolution code can increase the bit error rate by two orders of magnitude, to 10 -3 ~ 10-4,

and the Turbo code can further increase the bit error rate to 10-6. Because the Turbo code

has a coding performance close to the limit of Shannon theorem, it is adopted as the data

coding/decoding technology for 3G. The convolution code is mainly used for voice and

signaling of low data rates.

2.3.2 Principles of Interleaving/Deinterleaving

Interleaving/deinterleaving is an important step of the combined channel error correction

system. The actual errors in the channel are usually burst errors or both burst errors and

random errors. If burst errors are first discriticized into random errors, which are then

corrected, the systems anti-interference performance can be improved. The interleaver

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WCDMA Radio Theory

works to discriticized long burst errors or multiple burst errors into random errors, that is,

discriticized the errors.

The interleaving technology rearranges the coded signals by following certain rules. After

deinterleaving, burst errors are dispersed over time, making them similar to random errors

that occur separately.

2.3.3 Spread Spectrum

Spread Spectrum is an information transmission mode. It modulates information signals

with spreading code at sending end and enables spectrum width of information signals

much wider than bandwidth for information transmission. It dispreads at receiving end

with same spreading code, to resume data of transmitted information.

Figure 2.3-6 shows basic operations of spectrum spread/dispread. Supposing subscriber

data rate is R, subscriber data is 101101, and according to the rule that 1 is mapped as -1, 0

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

Spreading code is 01101001 in this example. Time each subscriber data bit to this code

series including 8 code chips. Concluded data rate after spread is 8 R and is random, like

spreading code. Its spread spectrum factors are 8.

Broadband signals after spread spectrum are transmitted to receiving end via radio

channels. Time code sequence with same spread spectrum code (dispreading code) whendispreading at receiving end to resume original subscriber data.

Spreading signal speed by 8 times factor may result in bandwidth spreading of subscriber

data signals (therefore, CDMA system is often called spread spectrum system).

Dispreading resumes signal rate to original rate.

Figure 2.3-6 Spectrum Spreading/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 spectrum to different subscriber can distinguish different


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subscriber, as shown in above sector.

Supposing that there are three subscribers and that signals they send are b1, b2 and b3,

spread their signals with spreading code of c1, c2 and c3 and final sending signal is

y=b1c1 + b2c2 + b3c3. Supposing that there is no interference in signal transmission, the

receiving end:

Gets signals after dispread with c1

z1 = y * c1 = c1 * (b1c1 + b2c2 + b3c3) = b1 + (b2c2c1 + b3c3c1)


z2 = y * c2 = c2 * (b1c1 + b2c2 + b3c3) = b2 + (b1c1c2 + b3c3c2)


z3 = y * c3 = c3 * (b1c1+b2c2+b3c3) = b3 + (b1c1c3 + b2c2c3)

All parts in the brackets in above three formulas are interference of other subscriber

signals to this signal. This interference can be absolutely avoided if using orthogonal

codes. orthogonal code is the code that is 1 after timing itself and is 0 after timing other

codes. So:

z1 = y * c1 = c1 * (b1c1 + b2c2 + b3c3) = b1 + (b2c2c1 + b3c3c1) = b1 + 0 + 0 = b1



2.3.4 Modulation and Demodulation

Modulation is the process to use one signal (know as modulation signal) to control another

signal of carrier (known as carrier signal), so that a characteristic parameter of the later

changes with the former. At the receiving end, the process to restore the original signal

from the modulated signal is called demodulation.

During signal modulation, a high-frequency sine signal is often used as the carrier signal.

One sine signal involves three parameters: amplitude, frequency and phase. Modulation of

each of these three parameters is respectively called amplitude modulation, frequency

modulation, and phase modulation.

In the WCDMA system, the modulation is Quaternary Phase Shift Keying (QPSK). If

High Speed Downlink Packet Access (HSDPA) is used, the downlink modulation mode

can also be 16QAM.

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Modulating rate of WCDMA uplinks/downlinks are both 3.84Mcps and modulate

complex-valued code chip sequence generated by spread spectrum in QPSK mode.

Figure 2.3-7 shows uplink modulation and Error: Reference source not found shows

downlink modulation.

Figure 2.3-7 Uplink Modulation

S

Im{S}

Re{S}

cos(t)

Complex-valuedchip sequencefrom spreadingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-shaping

Figure 2.3-8 Downlink Modulation

T

Im{T}

Re{T}

cos( t)

Complex-valuedchip sequencefrom summing

operations

-sin( t)

Splitreal &imag.

parts

Pulse-shaping

Pulse-shaping

Wcdma p&o b en Radio Theory 1 31

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