01_Introduction to UMTS

8/11/2019 01_Introduction to UMTS

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Nokia Networks Oy 1 (42)

SYSTEM TRAINING

Introduction to UMTS

Training Document


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2 (42) Nokia Networks Oy CTXX5317enIssue 3.0

The information in this document is subject to change without notice and describes only the productdefined in the introduction of this documentation. This document is intended for the use of NokiaNetworks' customers only for the purposes of the agreement under which the document issubmitted, and no part of it may be reproduced or transmitted in any form or means without theprior written permission of Nokia Networks. The document has been prepared to be used byprofessional and properly trained personnel, and the customer assumes full responsibility whenusing it. Nokia Networks welcomes customer comments as part of the process of continuousdevelopment and improvement of the documentation.

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Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.

Copyright Nokia Networks Oy 2005. All rights reserved.


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Contents

1 Module objectives ..................................................................................4

2 Background and history........................................................................52.1 Specification process for UMTS...............................................................72.2 UMTS network structure ........................................................................11

3 Network evolution................................................................................153.1 Starting with the basic GSM...................................................................153.1.1 GSM network elements..........................................................................163.2 Adding value to GSM networks..............................................................173.3 Adding value with GSM phase2+ and IN services .................................183.3.1 IN services .............................................................................................183.4 Increasing data transfer in existing GSM networks................................193.4.1 Benefits of faster data and services .......................................................193.5 Evolving GSM to packet core.................................................................20

3.6 Increasing speed with EDGE .................................................................213.7 Evolving towards to the universal mobile network (Service platform) ....223.7.1 UMTS development ...............................................................................233.7.2 Service potential in the mobile information society ................................233.8 3G end-to-end IP solutions ....................................................................23

4 Basics of the air interface and the path to WCDMA..........................254.1 Wireless principles .................................................................................254.1.1 Duplex transmission...............................................................................254.1.2 Radio communication.............................................................................264.1.2.1 Frequency Division Multiple Access (FDMA) .........................................274.1.2.2 Space Division Multiple Access (SDMA)................................................284.1.2.3 Time Division Multiple Access (TDMA) ..................................................294.1.2.4 Code Division Multiple Access (CDMA) .................................................314.2 CDMA background.................................................................................324.3 Principles of CDMA ................................................................................324.3.1 CDMA information, theory and codes ....................................................344.3.2 Spread spectrum and the principle of direct sequence CDMA...............354.4 Motives for using WCDMA in UMTS ......................................................374.4.1 Features of WCDMA in UMTS ...............................................................37

5 User Services .......................................................................................39

6 Review questions.................................................................................40


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1 Module objectives

The aim of this module is to give the participant the introductory knowledge needed

for explaining how the UMTS network has evolved. Topics to be covered in this

module include understanding the historic factors driving the system developmentand the evolution of the mobile networks. Furthermore, the student should gain abasic understanding of the different types of the air interface and list the key benefits

of UMTS for the operator and the end user.

After completing this module, the participant should be able to:

List at least three significant events in the evolution of CDMA networks

List the four main network subsystems of UMTS Release 99

Explain how existing GSM networks have evolved to support additional

services and new technologies

Name the four basic air interface access technologies

List at least three key benefits of WCDMA and identify at least threeadvantages of 3G networks for both the operator and the end user

without using any references.


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2 Background and history

There are three different generations as far as mobile communication is concerned.

The first generation, 1G, is the name for the analogue or semi-analogue (analogue

radio path, but digital switching) mobile networks established after the mid-1980s,such as NMT(Nordic Mobile Telephone) and AMPS(American Mobile PhoneSystem). These networks offered basic services for the users, and the emphasis was

on speech and services related matters. 1G networks were mainly national effortsand very often they were specified after the networks were established. Due to this,

the 1G networks were incompatible with each other. Mobile communication was

considered some kind of curiosity, and it added value service on top of the fixednetworks in those times.

As the need for mobile communication increased, also the need for a more globalmobile communication system increased. The international specification bodies

started to specify what the second generation, 2G, mobile communication system

should look like. The emphasis on 2G is/was on compatibility and international

transparency; the system should be a global one and the users of the system shouldbe able to access it basically anywhere the service exists. Due to some political

reasons, the concept of globalisation did not succeed completely and there were

some 2G systems available on the market. Out of these, the commercial success

story is/was GSM(Global System for Mobile communications) and its adaptations:GSM has clearly exceeded all the expectations set, both technically and

commercially.

The third generation, 3G, is expected to complete the globalisation process of the

mobile communication. Again there are national interests involved. Also some

difficulties can be foreseen. Several 3G solutions were standardised, such as UMTS(Universal Mobile Telecommunications System), cdma2000, and UWC-136

(Universal Wireless Communication).

The 3G system UMTSis mostly be based on GSM technical solutions due to tworeasons. Firstly, the GSM as technology dominates the market, and secondly,

investments made to GSM should be utilised as much as possible. Based on this, the

specification bodies created a vision about how mobile telecommunication willdevelop within the next decade. Through this vision, some requirements for UMTS

were short-listed as follows:

The system to be developed must be fully specified (like GSM). The

specifications generated should be valid world-wide.

The system must bring clear added value when comparing to the GSM in allaspects. However, in the beginning phase(s) the system must be backward

compatible at least with GSM and ISDN.

Multimedia and all of its components must be supported throughout the

system.

The radio access of the 3G must be generic.

The services for the end users must be independent: Radio access and the

network infrastructure must not limit the services to be generated. That is, the


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technology platform is one issue and the services using the platform totally

another issue.

In order to appreciate the work in creating standards like UMTS, it is helpful tounderstand the history and background of wireless communications in general, as

well as GSM and CDMA. A timeline of significant GSM and CDMA events is

contained in the following table.

Table 1. Significant events

Year Event

1900 In December, the first human voice transmission via radio wasaccomplished by Reginald Fessenden.

1906 First radio broadcast (also Reginald Fessenden).

1948 John Pierce writes a memo describing CDMA multiplexing.

1949 Claude Shannon and John Pierce describe major CDMA effects.

1956 Antimultipath RAKE receiver patented.

1970s CDMA used in several military communication and navigationsystems.

1980s Studies for narrowband CDMA for mobile cellular systems.

1981 Nokia introduces Nordic Mobile Telephone System (NMT).

1982 CEPT established Groupe Spciale Mobile by the joint proposal ofthe Nordic countries and the Netherlands.

1983 Advanced Mobile Phone System (AMPS) introduced.

1985 ITU starts studies for Future Public Land MobileTelecommunication Systems (FPLMTS).

A decision made on GSM time schedule and action plan.

1986 Eight experimental GSM systems are tested in Paris.

1987 Memorandum of Understanding (MoU); the services of the GSMsystem will be offered in all of western Europe.

A decision on system parameters and preparation of draftrecommendations.

1989 Final GSM recommendations and specifications.

1990s Studies for wideband ~5 MHz CDMA for mobile cellular systems.

1991 First official GSM call in the world was made on January 7thusing

Nokia equipment.

1992 GSM system ready in capitals and international airports. DCS1800 start-up implementation.

In February, the World Administrative Radio Conference allocatesinitial global radio spectrum for 3

rdgeneration mobile systems in

the 1885 2025 and 2110 2200 MHz frequency ranges.


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Year Event

1993 Major European urban areas have GSM coverage.

2nd

generation mobile system using narrowband CDMAstandardised in USA; it is called IS-95 (Intermediate Standard).

1994 ARIB in Japan forms a special group for FPLMTS radio interfacedevelopment.

1995 GSM covers main transportation links between major urban areas.

1996 UMTS Forum formed to raise market awareness.

In December, ETSI SMG2 forms study group for UTRA.

1997 ITU changes FPLMTS name to International MobileTelecommunications 2000 (IMT-2000) during WARC-97.

ITU requests proposals of Candidate Radio TransmissionTechnologies (RTTs) for IMT-2000 Radio Interface.

1998 In June, ITU receives 10 proposals for terrestrial RTTs and five for

satellite RTTs. These include CDMA2000 from the USA, ARIBW-CDMA from Japan, and UTRA from Europe.

3GPP formed to co-ordinate the development of a joint 3rd

generation system based on evolved GSM core and UTRA airinterface.

1999 ETSI start UMTS project to co-ordinate European 3rd

generationnetwork development.

In January, four operators are given 3rd

generation mobile networkoperating licenses in Finland.

2003 Commercial use of WCDMA systems.

2005 First commercial launch of HSDPA network.

2.1 Specification process for UMTS

As the 3G system is expected to be global, world-wide and generic, the specificationbodies related are also global ones (see the following list). In addition to the


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specification bodies, the specification process includes co-operation of operators and

manufacturers.

3GPP - Third Generation Partnership Project

ARIB- Association of Radio Industries andBusinesses

CWTS- China Wireless TelecommunicationStandard group

ETSI- European TelecommunicationsStandards Institute

T1- Standards Committee T1 Telecommunications

TTA- Telecommunications Technology Association

TTC - Telecommunication Technology Committee

GSM - Global System for Mobile communications

UMTS - Universal Mobile TelecommunicationsSystem

IETF - Internet Engineering Task Force

ITU-R - International Telecommunication Union -Radiocommunication

ITU-T- International Telecommunication Union -Telecommunication Standardisation

Figure 1. 3G specification bodies

There are four international standardisation bodies acting as generators for

3G specification work:

ITU-T (International Telecommunication Union)

This organisation provides in practise all the telecommunication branchspecifications that are official in nature. Hence, these form all the guidelines required

by the manufacturers and country-specific authorities. ITU-T has finished its

development process for IMT2000, International Mobile Telephone 2000. IMT-

2000 represents a framework on how the network evolution from a second to a thirdgeneration mobile communication system shall take place. Even more important,

different radio interface scenarios were outlined for 3G systems (see figure below).


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Direct Spread(on pairedfrequency

spectrum)

CDMA

Multi Carrier(on pairedfrequency

spectrum)

Time Code(on unpaired

frequency

spectrum)

Single Carrier(on pairedfrequency

spectrum)

Time Code(on unpairedfrequency

spectrum)

TDMA FDMA

cdma2000 UWC-136(EDGE)

(DECT)

IMT-2000radio

interfaceoptions

3G systems

UMTSFDD mode TDD mode

Figure 2. IMT-2000 framework and resulting 3G standards

ETSI (European Telecommunication Standard Institute)

This organisational body has had a very strong role when GSM Specifications weredeveloped and enhanced. ETSI is divided into workgroups named SMG (number),

and every workgroup has a specific area to develop. Because of the GSMbackground, ETSI is in a relatively dominant role in this specification work.

ARIB (Alliance of Radio Industries and Business)

ARIB conducts studies and R&D, establishes standards, provides consultationservices for radio spectrum coordination, cooperates with other overseas

organizations and provides frequency change support services for the smooth

introduction of digital terrestrial television broadcasting. These activities areconducted in cooperation with and/or with participation by telecommunication

operators, broadcasters, radio equipment manufacturers and related

ANSI (American National Standard Institute)

ANSI is the American specification body that has issued a license for a subgroup to

define telecommunication-related issues in that part of the world. Because of somepolitical points of view, ANSIs role is relatively small as far as UMTS concerned.

The ANSI subgroupis mainly concentrating on a competing 3G air interface

technology selection called cdma2000.

In order to maintain globalisation and complete control of the UMTS specifications,

a separate specification body called 3GPP(3rd

Generation Partnership Project) was

established to take care of the specification work in co-operation with the previouslylisted institutes. The outcome of the 3GPP work is a complete set of specifications

defining the 3G network functionality, procedures, and service aspects.


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3G.IP

OHG

UMTS

Figure 3. 3rd

Generation Partnership Project (3GPP) standardisation bodyfor UMTS

Because there are some political desires involved, the issue is not as simple asdescribed; global system means global business and this is why there has been a lot

of pressure to select or emphasise certain solutions more than others. This political

debate actually delayed the specification work remarkably, and finally anorganisation was established to take care of the harmonisation issues. This

organisation, OHG (Operator Harmonisation Group) aims to find a common

understanding concerning the global issues. The results of this organisation are usedas inputs in 3GPP work as well as in 3G future implementations. The OHG made its

maybe the most remarkable decision in April-May 1999, when it decided thecommon-for-all-variants code word (chip) rate in the 3G WCDMA air interface.

This issue has a direct effect on the system capacity and implementation and it wasmaybe the biggest delaying factor concerning the UMTS specifications.

The aim of the OHG work is to affect the specifications so that all radio accessvariants are compatible with all the variants meant for switching; this will ensure

true globalisation for 3G systems.

The first UMTS release was frozen in December 1999. This release is called UMTS

Release 99. In UMTS Release 99, the specification body 3GPP concentrated on twomain aspects:

Inauguration of a new radio interface solution. A new 3G radio interface

solution must use the radio interface resources more efficient than it is thecase with 2G radio interface solution. In addition to that, it must be very

flexible in terms of data rates to allow a wide range of applications to beserved.

The UMTS radio interface solutions are based on the multiple access


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principle CDMA. CDMA stands for Code Division Multiple Access. In

UMTS Release 99, CDMA is applied on 5 MHz carrier frequency bands.

This is the reason, why in some areas of the world, UMTS is calledWideband CDMA (WCDMA).

Two radio interface solutions were specified with UMTS Release 99:

The FDD-modecombines CDMA with frequency division duplex, i.e.uplink and downlink transmission are realised on separate 5 MHz frequency

carriers

The TDD-modecombines CDMA with time division duplex, i.e. uplink anddownlink are made available of the same 5 MHz frequency carrier, separated

by time.

Network evolution: GSM is nowadays the dominating mobilecommunications technology. In order to protect the investment of a large

number of mobile operators, network evolution guarantees the re-use of the

existing core network and service infrastructure in UMTS. This was

archived in UMTS Release 99 by adopting an enhanced GSM core networksolution for the UMTS core network.

The next version of the 3GPP Specifications is Release 4, which was frozen March2001, and Release 5, which was frozen in March/June 2002. In Release 4 and 5, the

upgrades in the radio access and radio access network were minor. The main focus

lay on the core network and the service infrastructure. UMTS Release 4 included aspecification of the Multimedia Messaging Service (MMS), a new radio interface

solution for China called low chip rate TDD mode (or TD-SCDMA). While in

UMTS Release 4 the first steps toward a 3G All IP could be found, this was fully

specified in UMTS Release 5, including the IP Multimedia Subsystem (IMS).

2.2 UMTS network structure

The obvious lack of GSM systems is the bandwidth offered to the end user. In the

beginning the bandwidth offered to the end user was reasonable, but as the technologydeveloped, the end user requirements increased. New services (such as the Internet)

became more common, so the bandwidth became inadequate. This was the main

reason for starting the specification for the next generation cellular networks. As

mentioned earlier in this document, one of the requirement points was that the airinterface of the 3G should be generic. Roughly, this means that the radio part of the

network should be even more functionally separated than in the GSM. To clarify andspecify this, the call establishment related parts of the 3G network are expressed as

follows:


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WCDMA

ATM

Iu

NMSNMS

CNCNRANRAN

O&M

Uu

UEUE

UE = User Equipment

RAN = Radio Acces Network

CN = Core Network

NMS = Network Management System

Service

Platform

Service

Platform

Figure 4. 3G network principle diagram

The multiple access method used between the User Equipment (UE) and the RAN

(Radio Access Network) is called Wideband Code Division Multiple Access(WCDMA). The 3GPP is aiming to specify open interfaces also within the RAN in

order to guarantee multivendor scenarios. Despite this, it is reasonable to believe thatoperators will not select a large number of suppliers for the RAN, nor for the Core

Network (CN) implementation.

In GSM, we use TDM (Time Division Multiplexing) as the transmission method

between the different network elements. For UMTS, ATM (Asynchronous Transfer

Mode) has been chosen as the transmission method in the radio access network. Thebasic difference between TDM and ATM is that in TDM, we use timeslots for

conveying information between network elements. In ATM, on the other hand, the

data is transmitted in cells (packets) of fixed size across the network. (An ATM cellhas 48 octets of payload, 5 octets of headers.)

Also the interfaces within the CN and between the CN and the other networks can be

considered as open, but there may be several national limitations / enhancements /extensions present. The 3G network can also be presented as a collection of

management layers, which cover certain parts of the network.


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Mobility Management (MM)

Session Management (SM)

Communication Management (CM)

Radio Resource Management (RRM)

UE RAN CN

Figure 5. 3G network management layers

The radio resource management (RRM) is completely covered between the RAN and

the user equipment (UE) and it involves managing how the channels are allocated.

The core network (CN) domains control the mobility management (MM), session

management (SM) and call control layers. The functions depend on whether the corenetwork domain is the CS (circuit switched) or PS (packet switched). The higher-layer functions performed between the UE and CN are often called communication

management (CM). The CM entity covers the topics like call control (CC),

supplementary services (SS) and short message service (SMS). In the module UMTS

Traffic Management, these management layers are further explained.

The added value that the WCDMA brings into the 3G network is the wideband radioaccess, thus enabling a situation, in which the operator is able to offer completely

new services to the end users. The planned access rates to be offered with WCDMA

are roughly presented in Figure 6. In 3G networks, the user access rate will vary as afunction of the speed. It should be noted that the bit rates presented here are mainly

points of interest when data services are in question. The very basic circuit-switched

services, such as a plain voice calls, do not require these bit rates, but when the userchooses to use e.g. fast Internet or video phone services, the bit rates face the limits

as expressed in Figure 6.

The 3GPP Specifications have been designed to divide the service platformfrom

the physical platform. This means that the services are independent from the

physical network. In GSM, we use traffic channels to carry data from the terminal to

the core network. In UMTS, the physical network routes a bearer between theterminal and the core network. The bearer is variable in terms of speed and quality,

and it is allocated depending on the services the subscriber wishes to use. The

subscriber may also be using different bearers for different services simultaneously.


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Pedestrian & Office (


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3 Network evolution

How can GSM as a system be converted or upgraded further on to face the increased

requirements set by the cellular operators and their subscribers? When studying this

matter, it is relatively easy to realise that there are several steps as to how things willbe implemented. On the other hand, there are several "clans" being either for oragainst certain technical development step(s).

The majority of networks will support UMTS by evolving from GSM backbones.

Several public authorities have announced that it is not necessary to implement every

single step described here, but, by experience, a complicated technical concept must

be done in phases in order to guarantee final quality and better working equipment.

3.1 Starting with the basic GSM

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

Figure 7. Basic GSM network principle diagram


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3.1.1 GSM network elements

The GSM radio access network called BSS (Base Station Subsystem) consists of the

following elements:

BSC(Base Station Controller) is responsible for radio path and radio resource

management.

BTS(Base Transceiver Station) is the network radio terminal forming the air

interface that the MSs (Mobile Stations) use for network access andcommunication purposes.

TCSM(Transcoding and Sub-Multiplexer Unit) is the channel codingconverter making it possible to use more effective channel coding within the

BSS (transcoding), and thus enables saving in transmission costs (through

sub-multiplexing).

NSS (Network Switching (Sub) system), the switching part of the GSM network,

contains the following elements:

MSC(Mobile Switching Centre) performs the traffic path connections and isresponsible for the majority of the connection management related entities.

VLR(Visitor Location Register) contains subscription and securityinformation of the active subscribers located in the radio network part. The

nature of the data the VLR contains is not stable: when the subscribers changetheir location(s), the VLR data changes respectively.

HLR(Home Location Register) is the static data storage of the subscription

information. The HLR also contains the subscriber location information, butthe accuracy of this information is on the VLR level.

AC(Authentication Centre) maintains security information of thesubscriptions.

EIR(Equipment Identity Register) maintains security information related tothe mobile equipment, not to the subscription.

Figure 7 presents a very basic GSM network made strictly according to

specifications. That is, all possible open and proprietary interfaces are included. Thenetwork described above is always the first step when a new/old operator is starting

its GSM cellular business. The subscribers in this kind of network have all the basic

services available:

Speech, circuit switched data up to 9.6 kb/s, Facsimile Call forwarding, call barring, in-call services (Wait, Hold, Multi-Party)


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3.2 Adding value to GSM networks

The GSM Technical Specifications define certain interfaces, which make it possible

to add some value to the system. Through these interfaces, the operators connect the

Value Added Service (VAS) platform(s) into use.A typical VAS platform consists of two elements: Short Message Service Centre

(SMSC) and Voice Mail System (VMS). In other respects the GSM network is the

same as in the previous phase.

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

Value AddedService Platform(s):

SMSC, VMS

Figure 8. GSM & Value Added Services

The Short Message Service (SMS) has proven its potential in commercial use.Originally, the SMS was not seriously considered as a service at all and thus it was

very cheap to use. However (and partly surprisingly), the subscribers adopted thisservice and nowadays a remarkable share of the traffic in the GSM networks is SMS

based.

Another issue is the capacity offered. In this phase the capacity of the network is

(normally) drastically increased, and a clear difference between the analogue anddigital technology in this respect becomes evident.


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3.3 Adding value with GSM phase2+ and IN services

The control of the services provided by the basic GSM is relatively good. However,

these services are not very flexible. In other words, the basic GSM offers mass

service for mass subscribers. To change the situation, the IN (Intelligent Network)is integrated to the cellular network. The IN platform provides the operator the tools

for creating completely new services, as well as full access to modify existing ones,

even on a subscriber basis.

Value Added

Service Platform(s):

SMSC, VMS

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

IN

Figure 9. GSM Intelligent Network included

3.3.1 IN services

Fraud management is a very essential issue for the operators. For this purpose, the

basic GSM has two registers: AuC and EIR. However, these registers cannotguarantee that the subscribers pay their bills.

IN is maybe the most common and flexible way to create a service calledPrepaid,

where the prepaid customers have their own account (paid in advance) with a call

credit balance. During each call the account balance is regularly checked. When thebalance is 0 it is not possible to establish any calls. Naturally, the subscribers are

able to buy more airtime, thus increasing their account balances.

The Intelligent Network has the following advantages:

Possibility to differentiate and compete with services. Customer segmentation from the operators point of view.

Better utilisation of the service platform: VAS (Value Added Service)

components used in IN services.


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3.4 Increasing data transfer in existing GSM networks

The data transfer rate of the basic GSM is low. Thus, new concepts to tackle this

issue are introduced. The first one is HSCSD(High Speed Circuit Switched Data),

with its more effective channel coding. The enhancements allow the end user to havedata calls with bit rates like 40 60 kb/s. These enhancements require only very

limited changes in the existing network elements.

Value Added


SMSC, VMS

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

IN

IP Networks

HW/SW

Figure 10. Enhancing GSM High Speed Data

3.4.1 Benefits of faster data and services

HSCSD increases data transfer capability. Hereby, physical radio channels areallocated to the HSCSD subscriber on demand only one physical channel is

guaranteed to the subscriber. The operator can therefore optimise the radio interface

usage given the demand of normal GSM subscribers and HSCSD subscribers. A set

of coding schemes allows a dynamic adjustment of the amount of redundancy addedto the user information. This is done to maximise the throughput via the radio

interface.

Mobile phones usually have small screens. Therefore http-pages cannot be presented

in a satisfying way. WAP (Wireless Application Protocol) was introduced to

overcome this problem. This is a uniform way to browse the Internet from themobile station without any accessory equipment. Roughly, the WAP changes the

nature of the mobile equipment from pure mobile towards data terminal; the mobileable to use WAP is actually an ASCII based Internet browser.


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3.5 Evolving GSM to packet core

GPRS(General Packet Radio Service) is the way to transfer packet data over the

GSM air interface. This requires HW/SW changes in the existing network elements,

and some new elements as well. The termIP backbonerefers to the part of thenetwork handling packet switching and connections to the Internet and other data

networks. The basic packet switched data core consists of two major elements:

SGSN(Serving GPRS Support Node) and GGSN(Gateway GPRS Support Node).In addition to these, the IP backbone contains other routers, firewall servers, and

DNS(Domain Name Server).

Value Added


SMSC, VMS

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

IN

IP Networks

HW/SW

SGSN

GGSNIP Networks

Figure 11. GSM and packet switched data core

The traffic through the packet core is not equal when comparing to the MSC side:the packet core traffic uses free air interface slots and thus the capacity of the packet

connection varies all the time. This is the basic reason why the 2G packet traffic

does not have exact QoS (Quality of Service) classification in use; it is said that 2Gpacket connection QoS is best effort.

From the operator point of view, the packet connections increase traffic anyway andthe time slots not used by circuit switched services are in effective use.

Fast, wireless access to the Internet is enabled; theoretically, bit rates of

150 kb/sin optimal circumstances are possible. A subscriber can expect nowadays data rates

of about 30 to 40 kb/s. Packet data transfer does not waste the capacity (as the

HSCSD does on one physical channel). WAP and SMS will be utilised veryeffectively in the context of different services either provided by the operator or a 3rd

party.


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3.6 Increasing speed with EDGE

Within the existing knowledge and technology, it is possible to further enhance the

transferred bit rates up to the level of 384 kb/s for circuit switched services, and to a

level of up to 473 kb/s for packet switched services. This is achieved by introducinga new modulation scheme (8PSK), combined with sophisticated coding methods

over the air interface. These methods are backward compatible with the existing

GSM methods, and they form a concept called EDGE(Enhanced Data rates in GSMEnvironment). Please note that issues like availability of timeslots, and transmission

quality, affect the bit rates that can be obtained.

Value Added


SMSC, VMS

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

IN

IP Networks

HW/SW

Changes

SGSN

GGSN

IP Networks

TRX Change & TransmissionUpgrade

Figure 12. GSM - EDGE

This step will probably be the end point for several operators due to the licensingpolicy (country-specific regulations). On the other hand, some operators may skip

this phase and move on to the next step in this development path. EDGE utilises

everything built in the GSM, including the multiple access method used in the air

interface (TDMA, Time Division Multiple Access).

Because the channel coding methods experience remarkable changes in this step, the

spectral efficiencydoes not change: same kinds of time slots are still in use, carrying

traffic like they have been carrying in a normal GSM. Also from the network

planning point of view, the use of radio frequencies will not change. The changes in

the system are related to transmission and multiple time slot allocation required inPSTN connections.


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3.7 Evolving towards to the universal mobile network(Service platform)

3G has a completely new way to approach the termservice: all the services offered

should be independent from the technology platform. This really opens the windowsfor free, 3

rdparty service development. There will be several services, and the

majority of those will be based on the Internet in one form or another. In addition,

imaging (picture transfer) and video phoning will be interesting services.

Value Added

Service Platform(s):SMSC, VMS

MSC&VLR

HLR & AC & EIR

BSC

BSC

BTS

BTS

TCSM

TCSM

PSTN

ISDN

IN

IP Networks

HW/SW Changes

SGSN

GGSN

IP Networks

RNCBTSMGW

Figure 13. UMTS New radio access introduced: UMTS network architecture

If there is a possibility (as well as requirements and license), the operator may move

to a completely new level in service offering. This phase introduces new wideband

radio access technology, which, in the beginning, roughly equals the bit rates theEDGE concept is able to provide. The new radio access require new network

elements in the radio network: RNC(Radio Network Controller) and BS(Base

Station) The BS is referred to as Node B in the 3GPP specifications.

The new radio access introduced in this phase is, however, utilising the frequency

spectrum more efficiently; the data flow and its bit rate is not dependent on timeslots any more. When the radio access method was planned, the packet type of trafficwas especially considered.


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3.7.1 UMTS development

UMTS will be developed in releases like GSM. When the technology is more

mature, the services will be more sophisticated and involved in every area of life.

The structure of the network will change considerably. There will be several radioaccess technologies in use in parallel. The wideband communication has changed thestructure of the network equipment and transmission.

The trend is that packet switched traffic volume soon will dominate over circuit

switched. It is expected that circuit switched traffic is used only in special cases,

such as for real time services that have high Quality of Service (QoS) requirements.

3.7.2 Service potential in the mobile information society

The UMTS cellular network is tightly integrated to the society, and some other items

(like digital signature) are widely used. This offers the possibility to combine many

items together. For instance, banking and business can be done almost completelywirelessly. The 3G terminal is far more than a phone, it may act as a social security

card, passport, purse, etc.

The business model will change, too. In an ordinary 2G network the operator

provides most of the services. In UMTS network the operator can be considered as a

carrier provider. Some service providers use carrier provider resources to deliver

the service and the content of the service is provided to the service providers bycontent providers. This structure will create a lot of challenges to be sorted out when

integrating UMTS to the other networks and technologies.

3.8 3G end-to-end IP solutions

With UMTS Release 99, a radio interface solution was introduced to allow the

transport of a wide range of multimedia services. The transmission network solution


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of the UMTS radio access network is based on ATM (and an alternative

specification of IP transport partly exists), which guarantees flexible bearer

establishment in the radio access network. But the UMTS CN solution is still rootedin GSM, and this may impose limitations for multimedia applications. In UMTS Rel.

4 and 5, call-processing server solutions combined with media gateways were

specified for circuit and packet switched services to allow flexible bearerestablishment also in the core network. The specifications explicitly mention IP and

ATM as potential transmission solutions for the core network.

This means a core network evolution.

P S T N

I S D N

Figure 14. 3G IP Majority of the traffic over IP

The majority of the traffic is expected to be packet switched data transfer over IP

(its more mature variant(s)). That is, the IP is expected to fully support mobilitymanagement (if expressed in telecommunication terms). Additionally, in this kind of

environment the IP must fully support QoS (Quality of Service) thinking. These two

conditions are essential if cellular IP terminals are going to be used.


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4 Basics of the air interface and the path toWCDMA

Air interface is a very complicated part of the UMTS network, especially incomparison to actual 2G networks (such as GSM).

The following sections give a basic understanding of the air interface, which in turnhelps to gain a better understanding of the issues and properties of the WCDMA

interface.

4.1 Wireless principles

4.1.1 Duplex transmission

There are three ways to accomplish communications:

Simplex

Half-duplex

Duplex

Simplex has been used since the early 1900s. It is communication in a one-way

direction, such as AM and FM broadcast stations. Simplex uses one frequencybroadcast to one or multiple receivers.

Half duplex is communication in a two-way direction. However, only one person

may talk at a time, since half duplex uses only one frequency. Half duplex is oftenreferred to as push-to-talk (PTT).

Duplex is communication in a two-way direction on two frequencies. One frequencyis used to talk and the other one to listen. This is the modern way of cellular

communication.

There are two common ways to realise duplex transmission:

Frequency Division Duplex (FDD)In this case, frequency resources are allocated to the mobile communicationsystem. Some of the frequency bands are allocated to uplink communication

only, while other frequency bands are used for downlink communication. In

other words duplex transmission is enabled by using different frequency

bands, meaning that uplink and downlink are separated by frequency. Time Division Duplex (TDD)

In this case, one carrier frequency band is used for uplink and downlink

communication. The transmission is organised in time frames. Within in


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each time frame, some time resources are used for uplink transmission,

while the remaining ones are used for downlink transmission.

Frequency Division Duplex Time Division Duplex

frequency

tim

e

frequency

tim

e

Uplink

Uplink

Uplink

UplinkDownlin

k

Downlink

Downlink

Downlink

Figure 15. FDD and TDD

4.1.2 Radio communication

There are two basic formats used in the radio communication: analogue and digital.The commercially available analogue format has been used since 1900, while the

commercially available digital format was introduced in 1990. The differencebetween the analogue and the digital format is that when using analogue, a persons

voice signal is transmitted over the air, while the digital format uses a string of 1s

and 0s to represent the voice signal (Figure 16). If someone would lock on to the

frequency used for an analogue conversation, he/she could actually hear the users

voices. For that same situation in the digital format the observer would need todecode the 1s and 0s before hearing the conversation.

There are four basic air interface technologies used for communication:

Frequency Division Multiple Access (FDMA)

Space Division Multiple Access (SDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)

Both FDMA and SDMA were introduced in the analogue format. TDMA andCDMA technologies are based on the digital format.


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So you see bla, bla, bla, yada, yada110000110101100011101110001

Analogue

Digital

Figure 16. The difference between analogue and digital

4.1.2.1 Frequency Division Multiple Access (FDMA)

In December 1900, Reginald Fessenden accomplished the first human voice

transmission via radio. This first link was over a mile long. Six years later he

transmitted the first radio broadcast. Soon afterwards, Frequency Division Multiple

Access (FDMA) technology was used. Different broadcasts in the same geographicalregion could be heard by using different radio frequencies. That is the idea behind

the FDMA; the frequency range is broken down into unique bandwidths and

distributed to the users. FDMA is used in cellular communications. One frequency to

speak on and one to listen on; thus we have duplex communications. That waymultiple users can operate in a particular frequency spectrum.


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frequency

tim

e

mobile

pho

ne1

mobile

pho

ne4

mobile

pho

ne2

mobile

pho

ne3

carrier band

Figure 17. With FDMA, users transmit simultaneously using separatefrequencies

Early cellular systems (1940s - 1960s) used higher power and lower frequencies

compared to todays cellular systems.

4.1.2.2 Space Division Multiple Access (SDMA)

In 1946, Bell Telephone System planners started submitting proposals for a large-scale system that would satisfy the growing customer demand for more wireless

access. The idea behind the proposals was to break a huge geographical region intosmaller areas called cells. Each cell would use a frequency different than those of

its nearest neighbours to prevent any interference.

That is the idea behind the Space Division Multiple Access (SDMA), the same

frequency can be used multiple times in the same geographical region.

The advantage to this technology is increased network capacity. The easiest way forFDMA broadcasters to increase their coverage area is to increase their transmitting

power. However, increased power causes interference problems and increases the

distance before a frequency can be reused. SDMA can increase coverage by adding

more cells. Modern cellular uses higher frequencies and lower power. This causesless interference and reduces the frequency reuse distance. This technology emerged

with the offering of Advanced Mobile Phone System (AMPS) in the early 1980s.

Although this was a big capacity improvement, it soon ran into its limits. The

network planners made a few modifications to this design to increase capacity. Onesolution was to reduce the cell size even further and to add more cells to fill in the

newly created uncovered areas. A second alternative was to add another frequency to


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the existing cell, so that two calls could be placed from the same cell. Both of these

solutions, however, did not overcome the basic limit of one call per frequency.

Figure 18. Space Division Multiple Access

4.1.2.3 Time Division Multiple Access (TDMA)

The next step in providing greater network capacity was not only to divide

frequencies into different cells, but also to divide this frequency into different slices

of time. Originally, the frequency could only carry one conversation, but with the

Time Division Multiple Access (TDMA) technology, multiple users could carry onconversations using the same frequency in the same cell or space.

That is the idea behind TDMA; dividing the frequency into multiple time slices so

that multiple users can access the same frequency at the same time.

The commercially available products associated with this new technology are Digital

Advanced Mobile Phone Service (D-AMPS) and Global System for Mobile

Communication (GSM). D-AMPS was introduced in the late 1980s, and GSMbecame available in 1990. These two products are not compatible. D-AMPS is a

digital overlay to the existing analogue system AMPS for the purpose of increasingcapacity. GSM is standalone product with a digital format at its core.


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f1

f2

f3

f4

f5

f6

f7

f1

f3

f2

Figure 19. Time Division Multiple Access

TDMA frame

frequency

tim

e

TDMA frame

Mobile Phone 1

Mobile Phone 1

Mobile Phone 1

Mobile Phone 2

Mobile Phone 2

Mobile Phone 2

Mobile Phone 3

Mobile Phone 3

Mobile Phone 3

Mobile Phone 4

Mobile Phone 4

carrier band

Figure 20. TDMA divides the frequency into multiple time slices


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4.1.2.4 Code Division Multiple Access (CDMA)

Code Division Multiple Access (CDMA) also uses digital format. In CDMAsystems, several transmissions via the radio interface take place simultaneously on

the same frequency bandwidth. The user data is combined at the transmitters side

with a code, then transmitted. On air, all transmission get mixed. At the receiversside, the same code is used as in the transmitters side. The code helps the receiver to

filter the user information of the transmitter from the incoming mixture of all

transmissions on the same frequency band and same time. This is often representedby layers, as can be seen in the figure below.

In contrast to classical FDMA and TDMA systems, the same carrier frequency bandcan be used in neighbouring cells. Frequency reuse factor in CDMA is one.

Figure 21. Code Division Multiple Access


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Codes

Power (P)

Time

Frequency

Figure 22. CDMA is digital and identifies each conversation by a code ratherthan frequency or time slice

4.2 CDMA background

Code Division Multiple Access (CDMA) is a type of spread-spectrum; a family ofdigital communication methods that the military has used for some time dating back

to World War II. It is particularly useful to the military for two reasons: It provides protection from enemy jamming, because the spread signal is

difficult to interfere with.

It can conceal that any communication is taking place.

Even though CDMA was hypothetically possible in the late 1940s, it was notavailable to the civilian market for another four decades. A primary reason for this

was that low cost, high-density digital integrated circuits had to be developed to keepthe cost and the weight of the units down.

4.3 Principles of CDMA

CDMA can be compared to a room with people speaking different languages.


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Let us imagine that a corporate CEO is hosting a large multinational gathering. Our

host, having mastered many languages, is primarily the one making the conversation.

Our host demands that his guests speak in their native tongues.Our host, a true mediator, is able to interpret the conversations between guests if

they wish to talk with each other; he can fluently follow several conversations at the

same time. He can understand different speakers, all talking at the same time,because they speak in different languages.

He occasionally has to tell some guests, who tend to get carried away, to speak a

little softer; and he has to ask the soft speakers to talk more loudly so that he can

hear them better.

The party starts to mature and many more guests arrive. The overall volume begins

to rise, because there are more people speaking at the same time. The host asks theguests nearest to him to speak more softly, while he asks the ones further away to

please speak up.

CDMA functions are much like our party. The CEO hosting the party is our BaseStation (BS) and the guests are the Mobile Stations (MS). The different languages

correspond to codes in a CDMA system. The BS can tell the mobiles apart, eventhough they are transmitting at the same time, by the codes that they use. Each MSuses a separate code.

Figure 23. The CDMA multinational gathering


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4.3.1 CDMA information, theory and codes

FrequencyBand

SpreadingFactor

Power

WCDMAOriginating Bit Received Bit

Figure 24. General transmission principle

In direct sequence CDMA, the transmission takes place continuously. If one user

data bit has to be transmitted from the transmitter (e.g. the mobile phone) to thereceiver (e.g. the base station), a certain amount of energy is required. The amount of

energy depends on the distance of the transmitter from the receiver, the obstacles in

the transmission path, etc. The energy can be represented like a box having

specific volume. The energy/volume is constant - but the dimensions of the box canbe change. As can be seen above, the boxs volume is made of the frequency band,

transmitter power, and time for the transmission. In UMTS, the frequency band is

constant. The other two dimensions, power and duration for the transmission, aresubject to change. A high data rates means many bits in one second, so the duration

for each information bit is short. Consequently, the output power for each bit must

be high to keep the boxs volume at a specific, constant level. If the data rate goesdown, less information bits are transmitted in one second, and therefore the durationof one information bit is longer. If the energy for the transmission of the information

bit has not changed, the volume of the box is the same. Consequently, less outputpower is required at the transmitters side.


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Codes

Power (P)

Time

Frequency

Figure 25. CDMA Code Division Multiple Access

In direct sequence CDMA technology based systems (like WCDMA), every user isassigned a code/codes varying per transaction, i.e. the different users use separate

codes. These codes are called spreading codes. It should be noted that one user may

also use several spreading codes in certain situations. The user data is directlymultiplied with his code. This processes is called spreading. Then the user data is

transmitted via the common frequency band.

If the originating bit rate is low, the power required for transmission is small.

This kind of case can be seen as a narrow layer in Figure 25.

If the originating bit rate is high, is higher. This kind of case can be seen as a

thick layer in Figure 25.

4.3.2 Spread spectrum and the principle of direct sequence CDMA

There are several spread spectrum system designs:

In direct sequence spread spectrumwe spread or code the message we want to

send by directly multiplying it with a large bandwidth user-specific code called thespreading sequence.

Frequency hopping spread spectrumutilises the large system bandwidth byperiodically changing the carrier frequency of the narrowband message according to

a user-specific sequence.

Time hopping spread spectrumuses a user-specific sequence to key the transmitteron and off at equal duration time segments. Unlike GSM, there is no user-specific

timeslot.


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The direct sequence (DS) spread spectrum method is used in both the 2nd generation

CDMA systems (that is, IS-95) and in the new 3rd generation Wideband CDMA

(WCDMA) (UMTS and cdma2000).

Let us visualise the spreading process. We have the information bits with some

power per bits. The spreading signal is like a monster truck driving over the bits. Thebits get squashed and spread over the ground. The power that previously defined

the height of the bits is also flattened. The power is spread over the spectrum, that is,the power per unit bandwidth is small. This is our goal. For someone not knowing

how the information was actually squashed, it is very difficult to detect the presence

of a spread spectrum user. All one would hear is an increased amount of noise.

ff

ff

User AUser A

User BUser B

DataData Data afterData after

spreadingspreading

PP

PP

TransmissionTransmissio n

over the airovertheair

DespreadDespread

User A signalUserA signal

at the receiverat thereceiver

ff

ff

ff ff

Figure 26. Spreading and sharing the same space

In a spread spectrum system all the users are in the same frequency band. The

frequency band is not divided in time to the users as in GSM. All users may send atthe same time at will. The users information is spread over the whole frequency

band with a user-specific pseudo-noise(PN) signal, the spreading code. The

transmitted signal occupies a much wider bandwidth than would be necessary to

send the information. The bits in the spreading code are called chips.

In a multiple access environment, we will have at the receiver our spread spectrum

signal summed with the other user signals. Our receiver will decode the original

message fine as long as the noise caused by the other signals present is not too high.This is why we can say that each user is sharing a pool of power in the system.


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4.4 Motives for using WCDMA in UMTS

The UMTS specifications include 3rd generation mobile services platforms. Being

able to deliver wideband multimedia services is going to require a higher

performance standard than the current wireless standards. UMTS will smooth theprogress of new wireless wideband multimedia applications, while fully supporting

both packet and circuit switched communications (e.g. Internet and traditional

landline telephone). From the outset, UMTS has been designed for high-speed dataservices and Internet based packet data offering up to 2 Mbps in stationary or office

environments and up to 384 Kbps in wide area or mobile environments.

In UMTS Release 99, there are two WCDMA modes:

FDD modeFDD stands for frequency division duplex. Two separate 5 MHz frequency

bands are used one for uplink transmission and another one for downlink

transmission.

TDD modeTDD stands for time division duplex. Hereby, one frequency band is usedboth for uplink and downlink transmission.

In the FDD mode a continuous transmission in one transmission direction can take

place. The TDD mode is more similar to GSM. Bursts are transmitted. The reasonfor that is routed in the fact, that uplink and downlink transmission must be managed

on the same frequency bands at different times. The FDD mode is seen as a very

good solution to get coverage. The TDD mode is especially efficient, when there is

asymmetric traffic. Because of this and its bursty nature, it use is seen mainly in thepico and micro cell environment.

Both in the FDD and TDD mode, direct sequence CDMA is applied. The radiointerface solution is called Wideband CDMA (WCDMA), because 5 MHz carriers

are used.

4.4.1 Features of WCDMA in UMTS

WCDMA for UMTS has several advantages, for example:

Efficient use of the radio frequency spectrum

Different technologies, which improve the spectrum usage, are easy to apply to

CDMA. E.g. in GSM, one physical channel is dedicated to one user for speech

transmission. If discontinuous transmission is applied, several timeslots of thephysical channels are not used. These timeslots cannot be used otherwise. In UMTS,

the transmission of several mobile phones takes place on the same frequency band atthe same time. Therefore, each transmission imposes interference to thetransmissions of other mobile phones on the same carrier frequency band. UMTS

supports discontinuous transmission via the radio interface. Consequently, if mobile

phones are silent, when there is nothing to transmit, the interference level is reduced


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and therefore the radio interface capacity increased. Another option allowed in

UMTS is the multiplexing of packet switched traffic with circuit switched traffic. If

there is no speech to transmit for a subscriber, the silent times are used for packetswitched traffic.

Limited frequency management

CDMA uses the same frequency in adjacent cells. There is no need for theFDMA/TDMA type of frequency assignment that can sometimes be difficult. This is

the main reason for increased radio interface efficiency of WCDMA

Low mobile station transmit power

With advanced receiver technologies, CDMA can improve the reception

performance. The required transmit power of a CDMA mobile phone can be reducedas compared to TDMA systems. In the FDD mode, where bursty transmission is

avoided, the peak power can be kept low. Continuous transmission also avoids the

electromagnetic emission problems caused by pulsed transmission to, for example,

hearing aids and hospital equipment.

Uplink and downlink resource utilisation independent

Different bit rates for uplink and downlink can be allocated to each user. CDMA

thus supports asymmetric communications such as TCP/IP access.

Wide variety of data rates

The wide bandwidth of WCDMA enables the provision of higher transmission rates.

Additionally, it provides low and high rate services in the same band.

Improvement of multipath resolution

The wide bandwidth of WCDMA makes it possible to resolve more multipathcomponents than in 2

ndgeneration CDMA, by using a so-called RAKE receiver. This

assists in lowering the transmit power required and lowers interference power at thesame time. The result is further improved spectrum efficiency.

Statistical multiplexing advantage

The wideband carrier of the WCDMA system allows more channels/users in onecarrier. The statistical multiplexing effect also increases the frequency usage

efficiency. This efficiency drops in narrowband systems with fast data

communications, because the number of the users on one carrier is limited.

Increased standby time from higher rate control channels

The wideband carrier can enhance the transmission of the control channels. The MSonly listens to the control channels part of the time, thereby increasing the standby

time.


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5 User Services

Subscribers are paying for value added services offered to them. Therefore mobile

operators are currently concentrating in broadening the services, offered to the

subscribers.

Access to a complete range of integrated, customer-friendly servicescustomised to their needs by operators and service providers. These services

will be available irrespective of the serving network and terminal, assuming

that similar capabilities are available. Where the capabilities are not available,

the user will be presented with a subset of the service.

Enhanced user service management covering the ability to customise and

configure the appearance and behaviour of user services and applications. This

management may include user interface customisation where the terminalsupports that capability.

Simplified service provisioning and service upgrades through the capability to

download new service applications with minimal customer interaction. Wireless personal Internet

information anywhere at

anytime.

Multimedia messaging

E-mail

Telecommuting

Improved quality of service

Support for video/audio clips

If the subscriber benefits from the UMTS introduction, so does the operator:

New service capabilities (means new business opportunity for operators)

Revenue opportunity with increased data/voice traffic

New frequency spectrum (new capacity)


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6 Review questions

Please take some time to answer the following questions.

1. Which of the following definitions for the abbreviation 3GPP is true?

a. It is a specification body organised by the manufactures to promote newtechnologies.

b. It is an EU organisation that specifies all the features that a 3G networkmust support.

c. It is an organisational body by the operators to promote theharmonisation of different 3G technologies.

d. It is the name of the interface between the RAN and the CN.

e. It is a specification body that takes care of the specification work in co-operation with many institutes.

2. Name the four subsystems in the UMTS network Release 99.

3. Which of the following elements is not part of the core network?

a. HLR

b. GGSN

c. RNC

d. EIR

4. Which of the following sentences about EDGE is true?

a. EDGE is needed to support IN prepaid services.

b. EDGE is using a more efficient coding and modulation technique than

in GSM to increase data throughput.

c. EDGE and GSM networks are incompatible.

d. EDGE will allow telephone calls to take place faster as people can talkfaster than in GSM.


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5. The SGSN is not needed to support 3G IP connections.

True False

6. List the four basic air interface technologies.

7. Which of the following is true (circle the correct answer)?

a. 1stgeneration networks are digital and 2ndgeneration networks areanalogue.

b. WCDMA is a 2ndgeneration technology.

c. TDMA and CDMA were introduced in 2ndgeneration networks.

d. Data, fax, and SMS services will first be introduced with WCDMA.

8. Describe the main difference between analogue and digital.

9. Which of the following are benefits of WCDMA (circle the correct answer)?

a. Improvement of Erlang capacity.

b. No frequency change allows imperceptible soft handovers.

c. New available frequency spectrum.

d. All of the above.

10. CDMA is an access technology, which was developed for high capacitycommercial mobile networks.


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True False

11. Which of the following are benefits or services for the end user?

a. Integrated services that may be customised per subscriber

b. Ability to download and activate new services at will

c. Multimedia messaging

d. Possibility for telecommuting

e. Improved quality of service

f. Videophony

g. Location-based services

h. Support for video/audio clips

i. All of the above.

Documents

01_Introduction to UMTS