01 Wo_bt01_e1_0 Umts Radio Theory-36

UMTS Radio Theory

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Contents

1 Overview of UMTS .................................................................................................................................... 1

1.1 Overview ........................................................................................................................................... 1

1.2 UMTS Technical Standards Development Trends ............................................................................ 3

1.2.1 3GPP Standard Development Status ...................................................................................... 3

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

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

1.3 IMT2000 Frequency Band Allocation............................................................................................. 15

1.4 Composition of UMTS System ....................................................................................................... 16

1.4.1 UE (User Equipment ) .......................................................................................................... 16

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

1.4.3 CN (Core Network) .............................................................................................................. 17

2 UMTS Technology Basics ........................................................................................................................ 21

2.1 Concept of UMTS Realizing Broadband Communication.............................................................. 21

2.1.1 Basic Concepts of CDMA .................................................................................................... 22

2.1.2 Basic Concepts of Spread Spectrum Communication .......................................................... 24

2.2 Transmission of Electric Waves in Mobile Environment ................................................................ 26

2.2.1 Features of Land Mobile Communication Environment ...................................................... 27

2.2.2 Signal Fading in Radio Path ................................................................................................. 28

2.3 Fundamentals of the UMTS Technology ........................................................................................ 28

2.3.1 Channel Coding/Decoding ................................................................................................... 28

2.3.2 Principles of Interleaving/Deinterleaving ............................................................................ 29

2.3.3 Spread Spectrum .................................................................................................................. 29

2.3.4 Modulation and Demodulation............................................................................................. 31

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2.4 Overview and Features of AMR ...................................................................................................... 32

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1 Overview of UMTS

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 to conduct 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 people’s

life and work.

The 3G mobile communication aims at meeting the future demand for mobile user

capacity 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.

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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 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, UMTS and TD-SCDMA. CDMA2000 and UMTS 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

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

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own technical advantages.

1.2 UMTS Technical Standards Development Trends

UMTS was originated by standardization organizations and manufacturers in European

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

and its standardization progresses smoothly. UMTS is the third generation mobile

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 14.4 Mbps within 5

MHz bandwidth.

The UMTS 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

1.2.1 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

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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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1.2.1.1 Basic Network Structure Based on R99

Figure 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. To guarantee the

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

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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 also improved by different degrees.

1.2.1.2 Network Structure Based on UMTS R4

Same as the R99 network, the basic structure of the R4 network consists of the core

network 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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BSS

BSC

RNS

RNC

CN

Node B Node B

IuPS

Iur

Iub

USIM

ME

MS

Cu

Uu

MSC server SGSN

Gs

GGSN GMSC server

Gn HSS(HLR)

Gr

Gc C

D

Nc

H

EIR

F Gf

Gi PSTN

IuCS

VLR B

Gp

VLR

G

BTS BTS

Um

RNC

Abis

SIM

SIM-ME i/f or

MSC server B

PSTN

cell

CS-MGW CS-MGW

CS-MGW

AuC

Nb

T-SGW R-SGW

Mc Mc

Nb

PSTN PSTN

Nc

Mc

Mh

A Gb

E

Figure 2 Basic Network Structure of the R4

1.2.2 Analysis on 3GPP standard Version Evolution

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

includes such key technologies as UMTS, 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

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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 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, UMTS 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. UMTS will be developing in total IP direction. In addition,

intercommunication of UTMS with other networks (such as, VLAN) and enhanced

MBMS will be increased.

1.2.3 Analysis on Evolution of 3GPP Technologies

1.2.3.1 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.


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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 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.

1.2.3.2 Evolution of Radio Access Network Technologies

High-speed broadband access

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

based on UMTS 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

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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 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, UMTS 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, amalgamation criteria with GERAN are under way, including

Iur-g, cell change that network aids.


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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 core switching 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 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

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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-GPS).

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.

1.2.3.3 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.


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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 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.

TE CNGateway

MT UTRAN CN IuEDGENODE

TE

End-to-End Service

TE/MT LocalBearer Service UMTS Bearer Service External

Bearer Service

Radio Access Bearer Service CN BearerService

RadioBearer Service

Iu Bearer Service

BackboneBearer Service

UTRAFDD/TDD

Service

Physical Bearer Service

UMTS

Figure 3 QoS Frame of 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

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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 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, amalgamation 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


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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).

1.3 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 4.

Figure 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 combined make the future spectrum for 3G reach over

500 MHz, reserving enormous resource space for future applications.

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1.4 Composition of UMTS System

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

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

called a UMTS 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.

1.4.1 UE (User Equipment )

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

Uu 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).

1.4.2 UTRAN (UMTS Terrestrial Radio Access Network )

The UMTS Terrestrial Radio Access Network (UTRAN) comprises Node B and Radio

network Controller (RNC).

1) Node B

As the base station (wireless transceiver) in the UMTS 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.


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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

the Iu 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.

1.4.3 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

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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 UMTS 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 UMTS 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.

The GMSC accomplishes the incoming and outgoing routing of the Visited MSC

(VMSC).

3) SGSN

As the functional node in the PS domain of UMTS core network, the SGSN

connects with 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.


19

The GGSN provides routes to the data packets between the UMTS 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 UMTS 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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2 UMTS Technology Basics

2.1 Concept of UMTS Realizing Broadband Communication

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

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

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

technologies.

UMTS bears following two meanings literally:

1. UMTS adopts CDMA communication technology

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. UMTS adopts wider spectrum

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

(spread-spectrum) with UMTS technology.Broadband signals have stronger

anti-interference ability than narrowband signals. Wider bandwidth realizes

RAKE receiving at subscriber end and increases communication quality.

Figure 5 shows UMTS 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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F

PowerDensity

F

PowerDensity

F

PowerDensity

F

PowerDensity

(1) Original Signal (2) Signal after spreadspectrum

(3)Meeting noise duringsignal transmission

(4) Signal and noise after spectrumdispreading

Signal Noise

Figure 5 UMTS Communication Principle

UMTS 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


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be dropped, affecting the service quality. Therefore, TDMA is not the best technology

for modern 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 in the Second

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

anti-interference military communications during the war. After 1960’s, it had been

used in military satellite communication. Later, it was developed by Qualcomm into a

commercial mobile communication technology.

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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 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


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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 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 (<1 W, usually 1 mW ~ 100 mW), and

can work in channel noise and hot noise background. Therefore, a frequency can

be easily reused in the same area, and the frequency can also be shared with the

now various narrowband communications.

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3. Anti multipath interference

In the wireless communication, anti multipath interference is a persisting problem

that is difficult to solve. With the correlation between spread spectrum codes, the

most powerful useful signals can be extracted from multipath signals at the

receiving end with a related technology. Also, the same code sequence waveform

from multiple paths can be added for reinforcement, to achieve effective anti

multipath interference.

4. Spread spectrum communication is a form of digital communication, particularly

suitable for synchronous transmission of digital voice and data. Spread spectrum

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, the

major 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


27

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

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.

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

mobile subscriber.

2.3 Fundamentals of the UMTS 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 efficiency by 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.


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Similarly, over a channel with fixed bandwidth, the total transmission code rate is fixed.

As channel coding 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 discretized into random errors, which

are then corrected, the system’s anti-interference performance can be improved. The

interleaver works to discretize long burst errors or multiple burst errors into random

errors, that is, discretizing 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 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.

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

channels. Time code sequence with same spread spectrum code (dispreading code)

when dispreading 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.

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

* Spreadspectrum

＋1

－1

＋1

－1

＋1

－1

＋1

－1

＋1

－1

Spectrum dispreading

Spectrum spreading

Figure 6 Spectrum Spreading/Dispreading in DS-CDMA

Distributing different spread spectrum to different subscriber can distinguish different

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


31

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

orthogonalized codes. Orthogonalized 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 UMTS system, the modulation is Quaternary Phase Shift Keying (QPSK). If

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

mode can also be 16QAM.

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

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

Figure 7 shows uplink modulation and Figure 8 shows downlink modulation.

S

Im{S}

Re{S}

cos(t)

Complex-valuedchip sequencefrom spreadingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-shaping

Figure 7 Uplink Modulation

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T

Im{T}

Re{T}

cos(t)

Complex-valuedchip sequencefrom summingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-shaping

Figure 8 Downlink Modulation

2.4 Overview and Features of AMR

Adaptive Multi Rate (AMR) code is a voice-coding plan. It is called broadband AMR

(AMR-WB or AMR Wideband) in UMTS.

Current GSM speech coding (FR, HR, EFR and AMR) is applicable to narrowband

speech and audio bandwidth is limited to 3.4 kHz. Audio bandwidth of AMR-RB

extends to 7 kHz, which makes the voice much clearer and natural, especially in

hands-free situations.

AMR provides eight coding rates of 4.7 k, 5,15 k, 5,9 k, 6,7 k, 7,4 k, 7,95 k, 10.2 k and

12.2 k. Select codes with low rate on condition that it does not influence

communication quality, to save network resource.

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01 Wo_bt01_e1_0 Umts Radio Theory-36