Wireless communications in the new millennium and third generation wireless networks

Rochester Institute of Technology

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Theses

Thesis/Dissertation Collections

2000

Wireless communications in the new millennium

and third generation wireless networks

Oz Yakuphanogullarindan

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Recommended Citation

Wireless

Communications

in

the New Millennium

and

Third

Generation

Wireless

Networks

By

6z

Yakuphanogullarindan

Thesis

submitted

in

partial

fulfillment

of

the

requirements

for

the

Degree

of

Master

of

Science

in Information

Technology

Department

of

Information

Technology

Rochester Institute

of

Technology

Rochester Institute of Technology

Department of Information Technology

Master of Science in Information Technology

Thesis Approval Form

Student Name:

Oz

Yakuphanogullarindan

Student Number:

_

Thesis Title:

Wireless Communications in the New Millennium

and Third Generation Wireless Networks

Thesis Committee

Name

Prof. Rayno Niemi

Chair

Prof. Bruce Hartpence

Committee Member

Mr. Rolando Henrich

Committee Member

Signature

Date

Thesis Reproduction Permission Form

Rochester Institute of Technology

College of Applied Science and Technology

Wireless Communications in the New Millennium

and

Third Generation Wireless Networks

I,

Oz

Yakuphanogullarindan, hereby grant permission to the Wallace Library of

the Rochester Institute of Technology to reproduce my thesis in whole or in part.

Any reproduction must not be for commercial use or profit.

TableofContents

Abstract

1. Introduction

1.1

Why

Third Generation?

1.2 Mobile Growth Forecast

1.3 CurrentandtheFuture UseofMobile Data Applications (The

Industry

convergenceto

IP)

2. Mobile Evolution

2.1 1st Generation Wireless

(

AMPS, TACS,

NMT,C450)

2.1.1 A Few ofthe

Analog

Cellular Systems in Detail

2.1.1.1 The Advanced Mobile Phone Service

(AMPS)

2.1.1.2 NMT (Nordic Mobile

Telephony)

2.1.1.3 TACS (Total Access Communications

System)

andOthers

2.2 2ndGenerationWirelessNetworks

2.2.1 GSM

2.2.1.1 GSM Services

2.2. 1.2 ComponentsoftheGSM Networks

2.2.1.2.1 MS (Mobile

Station)

2.2.1.2.2 BSS (Base Station

Subsystem)

2.2.1.2.3 Network Subsystem 2.2.1.3 Air Interface

2.2.1.4 Data in GSM

2.2.2 CDMA

2.2.2.1 Technical Characteristics

2.2.2.2 Spectral

Efficiency

Comparisonwith GSM

2.2.3 TDMA

3. FurtherStepsto3rd Generation :

HSCSD, GPRS, EDGE,

WAP

3.1

Why

The Need ForIntermediate Solutions? 3.2 HSCSD (High SpeedCircuit-Switched

Data)

3.3 GPRS

3.3.1 GPRS Characteristics 3.3.1.1 DataRates

3.3.1.2 Services

3.3.1.3

Quality

ofService

(QoS)

3.3.1.4 AllocationofRadio Resources 3.3.2 Interfaces : Air& Terrestrial

3.3.2.1

Gb, Gn,

Gi Interfaces

3.3.2.3 Air Interface

3.3.2.4 Physical & Logical Channels

3.3.2.5 Channel

Coding

Schemes 3.3.2.6 Allocation ofResources

3.3.2.7

Mobility

Management States

3.3.3

Internetworking

3.3.4 GPRSImplementationPath

3.4 _{EDGE (Enhanced Data Rates for GSM}

Evolution)

3.5 WAP (Wireless Application

Protocol)

3.5.1 WAP ApplicationDevelopment

3.5.2 WAP Model

3.5.3 WAPArchitecture

4. 3rd

Generation Wireless Networks

4. 1 3G Aims andObjectives

4.2

Terminology

4.3 Political Issues

4.4 Network Architecture

4.5

Mobility

Management States for 3G/UMTS

4.6 Air Interface

4.6.1 Physical & Logical Channels

4.6.2 Performance Improvements

4.6.2.1 Rake Receiver

4.6.2.2 Soft Handover

4.6.2.3 PowerControl

4.6.3 W-CDMA , TD-CDMA Comparison

4.6.4 Comparison oftheW-CDMAand cdma2000

4.6.5 Upgrade Path For CDMA Based2nd Generation Networks

4.7 Spectrum Allocation

4.8 Elements ofthe 3rdGeneration : Mobile

Station,

Software &

Security,

USIM

4.8.1 Mobile Station

4.8.2 Software

4.8.3 SIM Cards &

Security

- UMTS Subscriber

Identity

Module

(USIM)

4.9 Beyond 3G: Issuesand

Enabling

Technologies

4.10 Mobile Services offered

by

3r

generation

5. Conclusion : Upgrade

Paths,

Possible ProblemsandTime Scale

6. References

Abstract

-.th

Attheend ofthe20 century, and atthe

beginning

ofthis _one, wireless communications

are_{making large}advances. The newtechnologiesareonthe _waytoprovidea

high-speed,

high-quality

informationexchangebetween_{handheld terminals,} andinformation

repositories.Thesocalled 2,5 generation_{networks,using}the techniqueslikethe

HSCSD1, GPRS2, EDGE3,

andthe 3r generation wireless systems will

help

thewireless

worldtoreach thosegoals. InthisthesisIwill startfromthefirst andsecond-generation

wireless networks, andthen look intothe2,5 generation and 3rd

generation wireless

communications morein detail. The latestadvances inthe wireless world arethemain

focus ofthispaper although a short

history

ofwirelesscommunications isalso given.The

various aspects relatedto3rdgeneration systems will beexploredinthis_{thesis, for}

exampletheairinterface

discussions,

its time scale,itselements likethemobile

equipment,softwareandsecurity,

USLM4,

servicesthat willbe offered, etc. In_addition,

the technical factorsand

key

technologies that are

likely

to shapethewirelessnetwork

environmentofthefuture willbeexplored. Thispartisexpectedto

help

usto seebeyond

the3r generation.

1 _{HSCSD: High Speed Circuit Switched Data}

2_{GPRS: General Packet Radio Service}

3_{EDGE: Enhanced Data Rates for GSM Evolution}

4_{USIM: UserServiceIdentityModule isan}application_residingontheIC-Cardusedfor accessing UMTS

1.

Introduction

Developments in wireless communications attheend ofthe_{last century}andatthe

beginning

ofthis newmillennium are _{very important issues.}

They

arenot_onlyimportant

forthe _manymillions of people_{working in}thetelecommunicationsindustries butas well

forthe _manymillion userswho will profit out ofthenewwireless services willbe

offered.

Discussing

the so called2,5 generation_solutions,which are_{already starting}tobe

implemented

by

somewireless operatorsjust beforethe3rdgeneration networks _may

appear, is also_{very important in}

building

acompletepicture ofthe world of mobile

communications. The 2,5 generationsolutions arethe

GPRS, EDGE,

HSDSCD and

others,which aresimplerto start withforthewireless network operators andmuch

known today.

Following

thesepointsthe mostimportantpartto look into is the3rd

generation network standardization effortsandhow

they

_{may look like in}thefuture. The

new services,new

hardware,

new softwareandairinterfaces areimportantpointsto

checkout.

Discussing

the technicalissuesliketheair_{interface equally}withthenew

servicesthe3rdgeneration wireless networks will

bring,

isimportanttoseehowthe

subscribers willbe served. One ofthegoals ofthis thesisis to_equipthereader with

enough informationthathecan guesstheevolution oftheworldwide mobile

communication services andthenewfeatures itwillbe offeringoverthenextten years.

Oneoftheimportantmobile services will bethemobile multimediaservices, whose

evolutionwillbe influenced

by

theconvergence ofthe communicationstoIP and

by

the

evolutionofthenetworked multimedia servicesliketheones

heavily

usedthrough the

Thenew 3r

generation systemswilldeliver_{voice, graphics,}video and otherbroadband

information directto theuser, regardless of

location,

network orterminal.Thisnew

generation willrequirethe convergence ofthe_existingandfuturefixedand mobile

networks and_networkingprotocols. It is thought thattheunifiedairinterface frequencies

and standardization of allthe possible aspects will create atrustinthe systemsandwill

makeitattractivetoinvest inthemforthe_manyusers and operators.

3r

generation systems are expectedto

bring

lotsofbenefits like improvements in

quality,security, incorporationofbroadbandandnetworkedmultimediaservices,

flexibility

in servicecreation and ubiquitousservice portability. Inparticularthe

networked multimedia whichincludesservices suchas video- _and

audio-on-demand,

interactiveentertainment, educational andinformation services, and communication

services suchas _{video-telephony}and

fast,

large file transfersare expectedto usethemost

ofthe traffic_capacityavailable

by

thesystem.

1.1

Why

Third

Generation?

Inrecent yearsthere were_manyimprovementsmadeto the_existingmobile

phones andmobile networks.

Now,

there are_easyto_carryphones,voice_{quality is}

improvedand call dropouts happen less frequently. Howeverallthosesystems arestill

applicationslikethe _{audio, video,}real-time

videoconferencing

_{orhigh-speed Internet}

connection.

Another importantpointis thecomplicatedmobile standardsnowinusein

differentcountries and regions aroundtheworld. Dueto the_{increased mobility}of people

wedonowneed much morethaneverbefore a single global standardformobile

communications.

Usually,

whenwe travelaroundthecontinents ourmobile phonesdo

not always workbecausethe mobile networksfunction atdifferent frequencies anduse

differentprotocols.Ifwe wouldliketobereachable worldwide weneedtohave different

mobile phonesorwehaveto usephones which are abletooperate _{in many different}

frequencies5.

The oldergenerations ofmobilesystems were not designedtobeglobal systems

butrather national orregional.

So,

it is muchharderto

try

tostandardize theolderand

widely deployedsystems than

defining

thenextgenerationthat will solveallthose

incompatibility

problems.This is whattheorganizations like ITUandUMTS Forumor

ETSIare

trying

todo. Thenew generation,developed withthecooperationofallpossible

mobile

industry

_members, isexpectedtosolvetheproblem ofincompatible standards.

Those incompatibilities makethe life harderfortheequipment_producers,network

operators,managers oftheradio

frequency

spectrum, and

finally

forthe users, which

keep

thisbusiness running.

[2]

5_{Anexample ofthisistheTribandmobile phone of theMotorolaCompany,}whichoperates at 900, 1 800

1.2

Mobile Growth Forecast

Growthforecasts abouttheMobilecommunications are_{very important because}

thesenumbers show us _whythemobile communicationsis importantnowand _{why it}will

even get moreimportantwiththe3rdgeneration mobile systems.Anexample oftheir

importancecanbeseen

by

Figure.l,

which shows theknownand expected numberof

mobile subscribersbetween 1995-2010 in EU (European

Union)

countries [1]. The

Worldwidediagram aboutthenumber of mobile subscribersiseven moreimpressiveas

seeninFigure.2.

[1]

As it showsthenumberof subscribersis expectedtoreachto

nearly 2 billionworldwidein 2010.

[image:11.502.276.446.367.615.2] [image:11.502.55.233.368.619.2]

IMS 2D00 JQOi itMO

Figure. 1: European Union

Countries'

Mobile Subscribers

*[1]

D-;:-ft

:ccc Mi 501 D

Figure.2: World Mobile

As itcanbe seenfromthe

Figure.2,

takenfromtheUMTS Forum's

Report,

the

number of users ofterrestrialmobile servicesiscalculatedto bemorethan400million at

themoment. Thisnumberisexpected toincreaseto 940million

by

2005 andtomore

than 1.7 billionusers

by

2010. Thetotal_{number of users worldwideis derived}

by

_the

following

figures ofthedifferentregions.IntheNorth Americanumber of users willbe

around 190million

by

2005 and220million

by

_{2010. Thenumber of usersin Asia}

Pacificwill be 400million

by

2005,

and850 million

by

_{2010. In Western Europethis}

numberis expectedtobe 200million

by

2005 and260 million

by

2010. Intherest ofthe

world, therewillbe 150_{million physical mobile users}

by

_{2005 and400million}

by

2010.

Thepercentage ofthemultimedia usersin thosenumbers will_{be relatively}small

atthestartbuttheamountoftraffic

they

are_creatingwillbe huge. Forexamplein

Western Europethere will_{be nearly 32}million mobile multimediausers andthisnumber

isexpectedto increaseto90 million

by

2010.

Other importantmeasuresforthemarkets arethe financialmeasuresandthelevel

oftraffic. This kindofdatashowthata 104billionEURO6

per year mobilemarketis

forecasted forwesternEurope

by

2005,

whiletheamount oftotal trafficwillreach6,300

millionMbytes/month. Numberofmobile multimediauserswill_{be relatively}smallbut

thepercentage ofthemobilemultimedia within thefinancialfigures andtraffic volumeis

expectedtobe high. In theWestern European market mobile multimediatrafficis

expectedto be worth24billion EUROperyearin 2005 andit willbe usingthe3,800

6_{European Union'sunit of}

millionMbytes/monthoutofthe totalexpectedtrafficvolumeof6,300million

Mbytes/month.

[1]

Anotherpart ofthemobile marketistheSatelliteCommunication market.This is

animportantservicebecause itcan support theworldwide_coverage, which cannotbe

satisfied

by

terrestrial mobile services alone. UMTS Forum's forecasts show thatthe

world marketforphysicalusers ofmobile satellite services

(MSS)

(including

multimedia

MSS)

willbe 11.5 million

by

the year

2005,

_risingto 18.5 millionusers

by

2010.

They

expect 1 million MSSusersin Europe

by

2005,

_risingto 1.6million

by

2010.Ofthese

0.4million users areexpectedto bemultimediaMSS usersin

2005,

_rising to0.7 million

multimediaMSS users in Europe

by

2010. Totaltrafficlevels (multimedia +

non-multimedia)fortheEuropean MSS market will reach22millionMbytes/month in

2005,

risingto 40million Mbytes/month in 2010.

[1]

Thesenumbers _are, not_{surprisingly,}low

becausethe terrestrialconnectionsare_{in very}goodin shapein Europecomparedto the

rest oftheworld. Ofcourse, theproblemscaused

by

Iridiumcase7_has

restrained growth

of mobile satellite service usersbut it is

likely

to _{have only}ashorttermeffect andthe

expectednumbersin theEuropeanmarkets arestill asmentionedabove.

7_{Satellite Mobile Network}"Iridium"

could not gainenough subscribersa_longtime to_paytheirhigh

operationalcosts, that's theway company isplanedtobecloseddownandthesatellitesare plannedtobe deorbited. Iridium LLCannouncedthatitwasterminatingcommercialservice after 1 1:59p.m._(EST-USA)

March17, 2000,andthatitwas_beginningtheprocess ofliquidatingitsassets.Motorolais

looking

for

1.3

Today

& Future

Use

of

Mobile

Data

Applications

(Industries'

Convergence

to

IP)

An important issue forthegrowth ofthemobile networks willbe thedata

applications available withthe3rdgeneration mobile _networks, whichtodatewere not

veryuseful becauseofthe

failing

bandwidth and

technology

ofthe 2ndgeneration mobile

networks. Mobilecustomers wanttocontinue_makingvoice calls asusualbut

they

also

wantto be abletouse thee-mail, accessthecorporate

Intranets,

use e-commerce

solutions,use information services anduse allkindof_messagingservices.

They

would

liketoaccessthe

Internet,

make video_conferencingthrough theirmobile equipment with

onlyreasonabledelaysto runthe applicationseffectively.

Today,

theGSM network revenuesforthe mobiledata is around5% orlessofthe

totalGSMrevenues inmost ofthecountries. This isdueto the

following

reasons:

ExpensivePCcards, whichwere_proprietary for_connectingPC's totelephone

lines,

wereneeded.

Twophone lineswere needediftheuse ofdataand voiceisplannedonthe same

time.

Having

onlya 9.6or14.4Kbit/sec

(kbps)

transfer rate,which makesthedata

connections

boringly

slow andcostly.

All thesedisadvantagesarosedueto themissingconvergenceof communications

long

delays,

wecan still read our_e-mails,access theCorporate

Intranets,

sendSMS

messages. Howeverpoorbandwidth stillletsus down. Aswe allknowtheunbelievable

growth oftheInternet and multimediatechnologiesare_pushingthemobile worldtooffer

far bettersolutions as soon as possible.

Forthe nearfuture thereis nokillerapplication forwirelessdataexcept that

people wouldliketobereachable at all times.

They

wouldliketo

keep

theinformationin

the office or ontheroad_up todate. Ofcourse all theother multimedia services

mentioned above arenice tohavetoo. Companies inthemobile

industry

are awareof

thoseexpectations ofthehugeuser_groups, and_{manymergers, acquisitions,} and

partnershipsare

happening

to offerthe technologies ofthe

future,

which can meetthose

expectations.Wesee voicetraffic or_anyotherkindoftraffic _{is getting}convertedinto IP

trafficnowadays. This pointsthe_wayto theconvergence of relatedindustries intotheIP

technology. Butthe

industry

stillhasweaknesses which preventthis

being

arealsolution.

These deficienciesare thevoicegateways, endto endcontrol ofthe_{traffic, QoS}

(Quality

of

Service)8,

and network managementfacilities.Howeversolutions to theseproblems

are ontheir_wayandsoonthe

industry

we willbeable toofferallthoseandthe

industry

willconverge voice withtheIP

technology

anddatanetworks.Thiswillremove theneed

of

having

twodifferentnetworksforvoice anddata intheclosefuture.

8

QualityofService:thecollectiveeffect ofservice performancesthatdeterminethedegreeof satisfaction of a user of aservice.It ischaracterized

by

thecombined aspectsofperformancefactorsapplicabletoall

services,such as: serviceoperabilityperformance,serviceaccessibility performance,service_{retainability}

2.

Mobile Evolution

Oneneeds to understandtheevolution ofthe_{mobile networkstobeableto} understandthecurrent situationin thewireless communicationsworld.Forthispurpose,

a short section on the 1stGeneration Wireless

(AMPS, TACS, NMT, C450)

_{and a}

slightly

longersection on the2nd_{Generation Wireless Networksareincluded. This is because}

the

2n

Generation Wireless Networks are stillinplace all aroundtheworld and

they

_provide, formostofthewireless_operators, a_gatewayinto the3rd_{generation wireless networks.} Mostofthe operators will _probablyprefertoupgrade their2ndgeneration networks and

followtheintermediate stepsinsteadof_replacing thecomplete network with

3rd

generation hardwareand software. Below isa_summaryofthedifferentwireless systems

usedaround theworld.

Table. 1: The Tangleof2G Cellularand Cordless Standards *

[27]

Americas

Europe,

Africa

MiddleEast

Asia-Pacific

Japan

Others

Analogue

AMPS NMT JTAC NMT

CT1 TACS TACS

CT1 AMPS

Digital D-AMPS GSM PDC _GSM

PCS 1900 DCS 1800 CDMA CDMA

CDMA DECT,CT2 PHS CT2

[image:16.502.30.476.482.618.2]

2.1

1st

Generation

Wireless

(AMPS,

TACS, NMT,

C450)

Inthe_early

1980s,

developedcountries startedtointroducethe so-calledFirst

Generation Systems. Anexample ofthosecanbe seenwiththeAMPS in the

US,

TACS

inthe

UK,

andNMT inthe Scandinaviancountries.Thosesystemswere all_analogue,

offeringnational coverage and_{very limited}services. There were noreal concernsyetfor

aworldwide mobilesolution. Ashorthistorical outlookofsomeofthoseAnalogue

Cellularsystems couldbe listedas

following

[24]:

C-Netz- 450MHz

(C-450)

1981 Nordic Mobile Telephone

(NMT)

450- 450 MHz

1983 Advanced Mobile Phone Systems

(AMPS)

- 800MHz

Narrowband

Analog

Mobile Phone Service

(NAMPS)

1985 Total Access CommunicationsSystems

(TACS)

-by

Motorola,

900MHz

1985 Radiocom 2000

(RC2000)

1986 Nordic Mobile

Telephony (NMT)

900 - 900MHz

The

following

table aboutthe

Analog

Cellular Systems listsall ofthem. Someofthem

willbe discussedabitmorein detail lateron.

Mobile TX/ Base

TX(MHz)

Numberof

Channels

AMPS 824- _849/869-_{894 30}

832

USA,

Australia

TACS 890- _915/935-_{960 25 1000 Europe}

ETACS

872- _905/917-_{950 25 1240 UK}

NMT450 453- _457.5/463-_{467.5 25 180 Europe}

NMT900 890-_915/935- _{960 12.5 1999 Europe}

C-450 450- _{455.74/ 460-465.74 10 573}

Germany,

Portugal

RIMS 450- _455/460-_{465 25 200 ltalv}

NTT 925- _940/870-_{885 6.25 2400 Japan}

JTACS 915- _925/860- _{870 12.5 800 Japan}

2.1.1 A

Few

of

the

Analog

Cellular

Systems

in Detail

2.1.1.1

The

Advanced Mobile Phone

Service

(AMPS)

Oneofthose systems 'The Advanced Mobile Phone

Service'

(AMPS)

was

releasedin 1983. Itusedthe 800-MHzto900-MHz

frequency

bandandthe 30-kHz

bandwidthforeach channel asa

fully

automatedmobiletelephoneservice. It startedtobe

usedinthecitiesfirstandthenexpandedto therural areas.

[23]

AMPS,

wasusedthroughout theworld and wasparticularlypopularinthe United

States,

were_{revolutionary for its}time. Despitethis there arelimitations oftheAMPS aswith all

theother_analog systems. Thoselimitationsare:

Low calling capacityalthoughthe

frequency

reuseis implied

by

smaller

cells9-Limitedspectrum&no roomforspectrum growth.

Poor datacommunications possibilities.

Minimal privacyand security.

Tosolvetheproblem of_{low calling capacity 'Narrowband}

Analog

Mobile

PhoneService'

(NAMPS)

wasdeveloped lateron.NAMPS was anU.S. cellularradio

systemthatcombined_existingvoice_processing withdigital signaling,

tripling

the

capacityofAMPS systems. The NAMPS concept uses

frequency

divisiontoget3

channelsin the AMPS' 30-kHz single channelbandwidth. NAMPSprovides 3usersin an AMPSchannel

by dividing

the 30-kHz AMPS bandwidth intothree 10-kHzchannels. Of

course, smallerchannelsincreasethe_possibilityofinterference becausechannel

bandwidth isreduced.

[23]

2.1.1.2

NMT (Nordic Mobile

Telephony)

NMTis an _analogcellular standarddeveloped

by

Ericsson andusedin over40

countries aroundtheworld. Itoperates on two

frequencies,

450 MHz and900 MHz.

NMT 450i is justanimproved version ofNMT450. When itwasdeployed it hadagreat

opportunityof

being

able tousethe450 MHzand900 MHz systems,usingthesame

exchange and cell sites.

[25]

2.1.1.3

TACS (Total Access Communications

System)

and

Others

TACS started itscommercialcellularservicein UK in

January

1985. Aroundthe

sametime the

following

services wereintroduced: Nordic Mobile Telephone

(NMT),

C-450 in

Germany,

Radiocom 2000 in

France,

NTT in JapanandRadio Telephone Mobile

Systemin Italy.

2.2

2nd

Generation

Wireless Networks

GSM is themost common secondgenerationmobilesystem aroundtheworld. It

wasdesigned withthejointefforts ofthemanufacturers, regulators and service suppliers

mostlywithinEurope. Forthisreasonit firstbecame aEuropean standardandthenlater

was acceptedthrough theworld. CDMA technologies,which are collected underthe

name cdmaOne,aretheothersecond-generationsystems aftertheGSM. CDMAwas

launched laterthanGSM andalthough thereare_manyargumentsthatit isbetterasthe

Comparedto thefirst_generation,the secondgenerationsystems offeropen _standards,

digital

technology,

national coverage_roaming10, combinedvoice and data transmission,

and some_{supplementary} services11.Alloftheseare_{revolutionary}comparedtothefirst

generation networksbutstillnotenoughto havea worldwide standardized mobile

communication system.

2.2.1

GSM

Global System for Mobile Communications

(GSM)

is thewinner ofthe2nd

generation mobile worldfromthepoint ofview ofmarketshare. Itis usedin 120

countries aroundtheworld. An importantfeaturethatcauses GSMtobethe winneruntil

nowwasit's open architecture. Thisarchitecture allows operators tobe flexiblewith

equipmentselection andallowsthemto_{easily integrate}the latest

technology

advancements. The Global System for Mobile Communications

(GSM)

definesa

complete andintegrated digital cellularnetwork system. The developmentofGSM

startedin 1982 toovercome the_{difficulties arising from}theoperation of numerous

incompatible analogue cellular systemsthroughouttheEurope. Atthe starttheGSM

10_Roaming:the

ability fora user or mobileequipmenttofunction ina_servingnetwork. 1 1

Supplementaryservice: isa service whichmodifiesor supplements abasic telecommunicationservice. Consequently,itcannotbeofferedtoacustomeras astandaloneservice.Itmustbeofferedtogetherwith or inassociation withabasictelecommunicationservice.Thesamesupplementaryservice_maybecommonto

acronym stoodfor "Groupe Special

Mobile",

which wasthe _group

developing

the

standard.Butlateronthis waschangedtoGlobal System for Mobile Communications.

GSM is designedtooperatein the_primaryspectrum rangeof890-915MHz and

935-960MHz. The standard was releasedin

January

1990 andthe firstcommercial systems

werelaunched inthemiddleof 1992. Afterthe launchofGSM standard, theUnited

Kingdomrequested a specificationbasedonGSM but for higheruserdensitieswith

low-powermobile_stations, and_operatingat 1.8 GHz. The specificationsforthis system,

calledDigitalCellular System

(DCS1800)

werepublished 1991.

[20]

GSMnetworks _presentlyoperateinthreedifferent

frequency

ranges.These are[19]:

GSM 900 (alsocalled

GSM)

-operatesinthe900 MHz

frequency

range andisthe

most commonin Europeandthe world.

GSM 1800 (alsocalledPCN (Personal Communication

Network),

andDCS

1800)

-operates inthe 1800MHz

frequency

range. Itis available

by

_manycountriesin the

Europe.

GSM 1900 (alsocalledPCS (Personal Communication

Services),

PCS

1900,

and

DCS

1900)

- the

only

frequency

usedintheUnitedStatesandCanada for GSM.

GSMoffers_voice,

data, fax,

_{SMS (Short Message}

Service)

and some

supplementary

services, which are provided on

top

ofteleservices12

orbearer13 services.

Someofthemare call

forward,

call barring14 of_outgoingor

incoming

_calls, caller

identification,

call_waiting,

multi-partyconversations etc.

The dataservices offered

by

theGSMnetworks are _onlycircuit switched_services, and

they

are _onlylow speed. Thenewerapplications developed_{mostly for}multimedia

services15

cannotberun overthe lowspeed_{transmission links.}

2.2.1.2

Components

of

the

GSM Networks

Experts usually dividethe componentsoftheGSMnetworks into 3main

networkinggroups.

They

aredepicted inthe

following

figure.

[21]

12_{Teleservice:isatypeoftelecommunicationservicethatprovidesthe}

complete_capability,

including

terminalequipment_functions, forcommunicationbetweenusers_accordingtostandardizedprotocols and

transmissioncapabilities established

by

agreementbetweenoperators.

13

Bearerservice:isatypeoftelecommunicationservicethatprovidesthe_capabilityoftransmissionof

signalsbetweenaccess points.

14

Call Barring: Thisallowstoprevent_outgoingcallstocertainsets of_{destinations,} basedonthenumber

dialedand whethertheuserisroaming.InUMTS,it isproposedthatthisservice allowstoblock_outgoing

callsbasedon a wider range of parametersthatcouldincludefactorssuch asthe timeof_day,dayofweek,

location,typeof callrequested,cost oftheservice and/ordestination. It is invoked

during

theinitial outgoingcall_set-upprocedureand allowsthecalltobe blockedpriorto

incurring

_anycharges.This Servicecanbeappliedto_anyteleservicefor bothconnection-orientedandconnectionless-orientedservices. 15

Multimediaservice:Multimediaservices are servicesthathandleseveraltypesof media.Forsome

services,synchronizationbetweenthemediaisnecessary(e.g.synchronized audio and video).A

multimedia service_{may involve}multipleparties,multipleconnections,andtheaddition ordeletionof

SIM

ME

1 _BTS

Sj

ps

BTS

Um s

Mobile

Station EaseStationSubsystem NetworkSubsystem

[image:24.501.51.384.50.243.2]

SIM SubscriberIdentityModule BSC Base Station Controller MSC MobileservicesSwitchingCenter ME Mobile Equipment HLR HomeLocationRegister EIR EquipmentIdentityRegister BTS Ba3e Transceiver Station VLR Visitor Location Register AuC Authentication Center

Figure. 3: Components ofGSM Networks

*[21]

But toexaminethemmore_closelyone coulddraw the

following

Figure.4and explain

the components asthefoliowings:

Figure. 4: Detailed Components ofGSM Networks

[image:24.501.49.344.371.558.2]

Inthe definitionoftheMSthereis Mobile Equipment

(ME)

and asmart card

called theSubscriber

Identity

Module (SIM).The SIM inserted intomobileequipment

provides theuser's

identity

independentofthemobile device. SIMsupportsUser

identification,

Location

Information,

Security

and_{ciphering functions. The SIM}card

containsthe International Mobile Subscriber

Identity

(EVISI)

usedto

identify

the

subscriberto the system,a secret

key

forauthentication16

and otherinformation. The

mobileequipmentisthephysicalhardwareofthemobile phone.The International

MobileEquipment

Identity

(IMEI)

is usedtodefinethe

identity

of_{any ME.}

2.2.1.2.2

Base Station Subsystem

The Base Station Subsystem

(BSS)

has theBaseTransceiverStation

(BTS),

the

Base Station Controller

(BSC),

andtheTranscoder

(XCDR)

orTranscoder andRate

AdapterUnit(TRAU). The standardizedAbisinterfacein BSSallows operationbetween

components made

by

differentsuppliers. It linkstheBSCanda

BTS,

and allowscontrol

oftheradioequipment and radio

frequency

allocationintheBTS.BSS takes the

responsibility forall radio aspects of

GSM,

removingthesefunctions fromtheMobile

Switching

Center (MSC). Inmobiledevicecrowdedareas_{many BTSs} are needed. BSC

manages theradio resources forone or moreBTSs.Itsmainfunction is thecontrol of

radios and_switchingfunctions. BTS istheactualbase station,whichcontainstheradios

thatcommunicatewith mobilephones, anantennasystem and_{supporting hardware}and

16_{Authentication: a}

propertybywhichthecorrectidentityof anentityorparty isestablished with a

software. TRAUortheXCDR is theinterfacebetween theMSC andthe BSS. The

speech withinthePSTN or

MSC,

whichis 64

Kbit/s,

isreducedto 13 Kbit/s atTRAU for

transmissionovertheairinterface.

[52]

2.2.1.2.3

Network Subsystem

TheMobile Services

Switching

Center

(MSC)

istheheartofthefixed

infrastructureand_{it is effectively}atelephoneexchangefor GSMmobile calls. Itmakes

theappropriate connectionsto establish_{telephone calls,} links theGSMnetworkintothe

PSTN,

handles the

billing,

fulfilsthefunctions likeregistration, authentication, location

updating,handovers and call_routingtoa_roaming subscriber.

The Home Location Register

(HLR)

andVisitor Location Register

(VLR),

together

withthe

MSC,

providethe_call-routingand_roamingcapabilitiesofGSM. The HLR

provides apermanent recordof all subscribers who

belong

to thehomenetwork.There is

onelogical HLRper networkbut it may be implementedasadistributed database.

The Visitor Location Register

(VLR)

holdssubscriberdetails

temporarily

whilstauser

iswithin aparticulargeographicalarea. Thismeans VLRhas alimitedversionofthedata

HLRholds but it has data fromthesubscribers oftheothernetworkswhilst

they

arein its

region.

Usually

thereis oneVLRperMSC_covering

typically

the areaof a city.VLR

couldbebuiltas anindependentunitbut_usuallyallmanufacturersof_switching

equipmentimplementtheVLRtogetherwiththeMSC.

TheEquipment

Identity

Register

(EIR)

isconcernedwiththe _{security features}ofthe

mobile equipment.It

basically

keeps adatabase thatcontains alist of all valid mobile

equipment onthe network. Asweknow itsInternational Mobile Equipment

Identity

(IMEI)

identifies each mobile equipment.An IMEI ismarkedasinvalid if it has been

reported stolen orisnottypeapproved. Thistypeofdevicesmightbe preventedfrom

accessing thenetwork. The devices arelisted inthreegroups fromtheIMErspoint of

view.The first group istheWhite-listed devices. Thoseareallowedto connectto the

network.Thesecondis theGrey-listeddevicesgroup.Those areunder observation from

thenetworkforpossibleproblems. Thethird_{group is}theBlack-listed devices. Those

haveeitherbeen reportedstolen, or are nottypeapproved(thecorrecttypeofterminalfor

aGSMnetwork). Because ofthosereasonsthese types ofdevicesarenot allowedto

connectto thenetwork.

[22]

The Authentication Center

(AuC)

isconcerned with _securityandciphering. It is

basically

aprotecteddatabasethatstores a_copyofthe secret

key

storedineach

subscriber's SIMcard whichis usedforauthentication and encryption overtheradio

channel.

Echo Canceller

(EC)

providescancellation of_upto68milliseconds of

delay

and

Internetworking

Function

(IWF)

provides an_{interface betweenGSM and other}

networksinvolvedinthetransportof userdata.

Operations

and

Maintenance

_Center

(OMC)

_{isacentralized}

control pointfromwhich

performance ofthe network can_{be remotelymonitored and controlled.}

There is normally

oneOMCper regional area on thenetwork.

Network Management Center

(NMC)

sits atthe

top

ofthemanagementhierarchical

treeandhasoverall_{responsibility}forthenetwork.

2.2.1.3

Air

Interface

GSM divides theavailable25 MHz bandwidth into 124carrierfrequencies spaced

200 kHzapartfrom each other.

[50]

It assigns oneormorecarrierfrequencies toeach

basestation. Then it divides thosecarrierfrequencies in time, usingaTime Division

MultipleAccess

(TDMA)

scheme.There are26 frames usedin its trafficchannels

(TCH). The length of a26-frame multiframeis 120ms. Out ofthe26

frames,

24are used

fortraffic, 1 isusedforthe Slow Associated Control Channel

(SACCH)

and 1 is

currently unused.TCHs forthe uplinkanddownlink are separatedintime

by

3 burst

periods,sothatthe mobile station doesnothaveto transmitand receive_{simultaneously,}

An importantpointforthe airinterfaceis interference. Electromagnetic

interference might cause errorsforwireless communications.Toprotect againstthose

errorsGSMuses convolutionalencoding17

andblockinterleaving18to protectitsradio

interface. Ofcoursethere are other problems asthereflected signalsbounceoff

everything likethe

buildings, hills,

_{cars, airplanes, trains,}etc.Becauseofthisreason

manyreflectedsignals,each withadifferent_phase,can reach an antenna. GSMuses

Multipathequalizationtoextractthedesiredsignalfromthe unwanted reflections.

Multipathequalization findsouthowaknowntransmittedsignalis modified

by

multipath

fading,

and

basically

constructs aninversefiltertoextracttherestofthedesired signal.

2.2.1.4

Data in GSM

Up

until nowdata

by

GSMnetworks were

basically

handledasdepicted inthe

following

Figure.5.

17_{Errorprotectioncode}

encoding data bits inacontinuous stream.Anerror correctioncodeinwhich each m-bitinformationsymboltobeencodedistransformedintoan n-bitsymbol_(n>m)wherethe

transformationisafunctionofthelast kinformationsymbols,andk isreferredtoastheconstraintlength ofthecode.Convolutionalcodes are often usedto improve theperformanceoftheradioand satellitelinks. [60]

[image:30.501.63.374.48.235.2]

Figure. 5: Data

by

GSMNetworks

A moredetailedpicture ofthisdatacommunicationmethod shows usthe

following

elements andinformationasinFigure. 6.

DTE

12 Kbit/secMl PCMCIA

12(22.8)Kbit/sec (33.8)K bit/sec

BTS

MODEM IWF

9.6 Kbit/sec

Rate Adapter

12(16) Kbit/sec

BSC

12(64) Kbit/sec

MSC

12(64) Kbit/sec

12(16) Kbit/sec

[image:30.501.60.445.340.549.2]

TRAU

Figure.6 : Data Communication Details in GSM

Here betweentheNotebookandtheGSMphonewehave 9.6 Kbit/secconnection

usedforthe data. Therearesome control signals used andthe actualbitrateis 12

error correction andtransmission andthevalueof22.8 Kbit/sec is reached whenthedata

ison theair. Ofcourse thereis another_waytoincrease thisvalue abitmore

by

leaving

theerror correctiontotheapplication level. Ifthenetworkis allowing this optionthenwe

canreach to 33.8 Kbit/secas seen inthefigure. But thisis notthepointwe shouldbe

really interested in. Themoreimportantpointisto seethe limitationsoftheGSM forthe

datatransfer.

By

looking

intothe_{way GSM data flows in} the

figure,

itcan_{easily be}seen

that the error correctionbitsare removed attheBSS

(BTS/BSC),

andthe 12 Kbit/sec data

whichisleft is sentto theTRAUat therates of16Kbit/sec.

TRAU,

adaptsthis to64

Kbit/sec

(padding)

to transfer toMSC. MSCrelaysthe signalsto theGSMnetwork_entity

knownas the

Internetworking

Function (IWF).

This,

which contains arate _adapter,will

removethe64 Kbit/secpadding,reconvertthe 12 Kbit/secinto original9.6 Kbit/sec data

plus thecontrol signals andfeedthatto themodem. This scenario_{is actually very}similar

when_connectingtothepacket networks liketheISDN. One difference isthat theDCEis

notamodembutanISDNconnector or aPacketAssembler/Disassembler(PAD). Butall

ofthose arestill intheIWFandtherate adoptionthrough theGSMnetworkis

unchanged.

GSMairinterfaceis thebottleneckofthedatatransferin GSMsystems. A single

timeslotcarries 22.8 Kbit/secor, withouttheerrorcorrection, 33.8 Kbit/sec. Butthiscan

beusedas9.6Kbit/secor 14.4 Kbit/secactual databecauseofthereasons explained

above. Round figureofthe_efficiencyofthe timeslotcouldbe calculated withthe

formula (data bits /all bitstransferred).Thismakes 9600 / 22800 =

0.4215,

_whichmeans

puncturingschemais changed, andmorebits are removedwith_{puncturing before data is}

ontheair. As seenin theFigure. 7 the290bitsaretransmittedon_{every 20ms}compared

to the240 bits sent

by

the9.6Kbit/sec case. 288 ofthosebitsareusedforthedataandthe

remaining 2are usedforthecontroldata. The airinterface isstill22.8 Kbit/sec asbefore.

GSMwith9.6 Kbit/sec datarate

240 bits

Block Code 240+4

244bits _1/2Rate Convolutional Code 488 bits Puncturing 488 32 % 456bits 22.8 Kbits/sec

GSMwith14.4 Kbit/sec datarate

290bits

BlockCode 290+4

294 bits 1/2 Rate Convolutional Code 588 bits Puncturing 588-132 456bits 22.8 Kbits/sec

Figure. 7: Channel

Coding

in GSM

Thereare several possibilitiestoreachto higherdatarates.One ofthemisto

reduce thecontrol signals_connectingtheDTE andDCE. _{Another possibility is}tousethe

errorprotectionbitsas data

bits,

andleavetheerror protectionto theapplicationlevel.

Anothersolution, which isusedin the

HSCSD,

iswhere several airinterfacetimeslots

canbe boundtogetherandthecompletebandwidth used.So ifallthe GSMtimeslotsare

used wecan reachto 8x22.8 Kbit/sec = 182.4Kbit/sec airinterfaceas a maximum.

CDMA is a"spreadspectrum"

technology, which spreadstheinformation

containedina particular signal ofinterestover a much greaterbandwidththan the

original signal. Itoffers, theoretically, 8to 10times_capacityofthe_{AMPS analog}system

and4to5 times thatof aGSMsystem. Itusesthe same

frequency

_{in every}sector of

everycell,enhances_privacyand supplies bandwidthondemand. The historicalevolution

ofthestandardisas seen

by

the

following

Figure. 8.

CDMA Celafar Concept Sin Diego CDMA demonstration KoiciS CDUAIS-95 standard S*ued Koreaselects COMA : PCSPriraeCe tans_up nationwide PCSttsnric*

in14cities

UJS. PCStsndsnl

Isteommercial COMftsyrtem

intHong Kib

Commercial

systems

"

100 UAcities

Japanselects COMA

CDMAsubstrings

re&ch overT2.5M

in38com* lies on5continents"

In Sept 41miton

ube<ribers, 50_operator), 2?nations wtcomsnrebl ysfems Morethan 65companies licensedto Midand *IIIS35 products

1989 1990 1993 1995 1996 1997 1998 1999

Figure. 8:

History

ofCDMA Standard

*[4]

2.2.2.1

Technical Characteristics

Sometechnical partofthe CDMAstandardcanbesummarized_{easily in} the table

belowwhich putstheCDMAchannelnumbertoCDMA

frequency

assignment

correspondencetogether.

Correspondence

*[26]

Transmitter CDMA

Channel

Number

Center

Frequency

of

CDMA Channelin

MHz

Bl

MobileStation

(800

MHz)

1 <=N<=₇₇₇

1013 <=N<= ₁₀₂₃

0.030 N+ 825.000

0.030

(N-1023)

+825.000

BaseStation

(800

MHz)

1 <= _N<=₇₇₇

1013<=N<= ₁₀₂₃

0.030 N +870.000

0.030(N-

1023)

_{+ 870.000}

Mobile Station

(1900

MHz)

0<=N<=1199 1850.000+0.050 N

BaseStation

(1900

MHz)

0<=N<=1199 1930.000+0.050 N

In CDMA anumberof users will haveaccessto the sameblockof spectrumatthe

sametime. Spread Spectrum Techniques asCDMA were usedin militaryapplications at

very startdueto the difficultiesof

intercepting

and

jamming

transmissions. Their

potential advantage ofhigh spectral_{efficiency led}to the_{company Qualcomm}

developing

aCDMAsystem which was_officiallyadoptedin 1993

by

theTelecommunications

Industry

Associationandbecome knownasInterimStandard

(IS)

95.

Themostimportanttechniquesusedin theSpread Spectrum Technologies arethe

Frequency Hopping

andDirect Sequence.

Frequency hopping

constantlychangesthe

transmission

frequency by

spreadingitacrossthe spectrum.It wasused

traditionally

for

of multipath propagation andfading. DirectSequenceas usedin IS95 spreadsthesignal

prior_{to modulation,} and produces a wide_{bandwidth baseband}andthenmodulates this

onto a single carrier.

In CDMAthe signals areburiedintothenoise.Thereforethe methodof_raising

them abovethenoiseis nota

frequency

filter buta code

filter,

becauseallthose signals

are onthesame

frequency

andinthenoise level.

Basically

priortomodulationthe

Modulo 2typeofdatasignal wewouldliketo transferis addedtoahigher bitrate code

as 1.2288 Mbpstoproduce a_{correspondingly}widerbandwidth signal. Atthe receiver

side we addto thecode again a modulo2signal andreproduce theoriginaldata. This

narrows and raisesthespectrum abovethebackgroundnoise suchthat_{it may be}

demodulated. Ofcourse

by

_using adifferentcodeforeachtransmissionwe can get_many

transmissions _occupyingthe sameblockof spectrum.Onthereceiversideall weneed is

touse theright codetopull theright signal out ofthatbackgroundnoise.

Thereareseveral

Spreading

andChannelization Codes usedinthe 1.2288 Mbps

code mentioned above.Thoseare added withtheModulo2makethe systemwork. One

ofthose codes isthe

Long

Code. Thiscodein IS95 is generatedfroma42-element shift

registerand_onlyrepeats once_{every 41 days. There is only}one

long

code defined in

IS95. Anotherone isthe

Long

Code Mask. This isa simple42-bitpattern usedto

modifythe

Long

Code. It is determined

by

theElectronic Serial Number

(ESN)

ofthe

mobileterminal andtherefore uniquetoeach mobileterminal. AnothercodeistheWalsh

means that_{if any}one sequenceiscomparedto _anyother sequencethen therewill be 32

bitsthatarethesame and32bitsthatwill_{be different.Theresultofthis is thatwhen}

looking

forone code _anyinterferencecaused

by

anotherWalsh Codeshouldproduce a

zero result.Walshcodes are usedto

identify

differentchannelsonthedownlink.

Thesimplifiedtransmitand receive process oftheCDMAcanbe shownasinthe

figure below. As seenthemodulo addition ofthe _spreadingcodes atbothtransmitterand

receiver providetheoriginaldataatthereceiver output. Inpracticethe transmitteris

much simplerthanthereceiver systemin CDMA. Receiver hasrakeand synchronization

components additionally. Spreading Code Digital Data _Digital Modulator Tx Radio Carrier W-CDMA Output Radio Modulator De-Spreading Code Digital Data Digital ; Demodulator Rx Radio Carrier Modulatec Carrier Radio Demodulator

Figure. 9:

Tx,

Rx Schema forthe CDMA

Somemorebasic characteristicsofthe CDMAsystemscanbeseeninthe tablebelow.

Multiple Access Schema Direct Sequence CDMA

Duplexing

Method FDD

Chip

Rate 3.84 Mcps

Bandwidth 5 MHz

Carrier

Spacing

200 kHz Raster

Frame Length 10ms

SlotsperFrame 15

InterCell Synchronization None

Spreading

Factor Variable

(4-512)

User Data Rate 8 -> 384 Kbps

2.2.2.2

Spectral

Efficiency

Comparison

with

GSM

CDMA is spectrallyefficient comparedto theGSM. AtasingleGSMcella200

kHzcarrierhasthe_abilityto_{carry up}to8 simultaneous calls.Thismeansthenet

bandwidthoccupied

by

each call is 25 kHz. Ata singleCDMAcell a 1.25 MHzcarrier

hasthe _abilityto_{carry 32}simultaneouscalls.This meansthenetbandwidth occupied

by

each callis 39 kHz. So it looks like CDMA is lessefficientusingthis comparison.But

when_considering a number of cellsin closeproximitythe situation changes. As known

GSMuses

frequency

re-use patterns andifweconsiderapatternof7 is usedthe

calculationchanges. 7x200KHz = 1.40MHz isusedcomparedto the 1.25 MHz ofthe

CDMAuses. Andthenetbandwidthoccupied

by

each call is still25 kHz. Thismeans in

the7 cells wecan _carry7x8=56calls atmaximum. ButtheCDMAcan use thesame 1.25

possiblewiththe CDMA systemandthe netbandwidth occupied

by

each callis 5.5kHz

comparedtothe25 kHzoftheGSM.

Butthespectral_efficiency doesnot mean unlimited number oftransmissionswillbe

possiblewiththe CDMAtechnology.

Soft

Blocking

Astherecanbealmostinfinitenumberof codesgeneratedit is

theoretically

possibletohave unlimited number oftransmissionson a singlecarrier.But in practice

thisisnot_{the situation,} becausethenoiselevel increases withthe additional number of

transmissionsandbecomesa

disturbing

backgroundnoise.This waythe_qualityofthe

callsdeteriorates dueto thebackgroundnoise. Soft

blocking

isatermusedtodescribe

customers

hanging

_{up due}to this

deteriorating

_qualityand_{creating kind}of a self

controlled_regulatingsystem.But in realitynetwork operators would not desiresuch a

situation andreal system parameters will _actuallycause a hard limitto thenumber of

calls on acarrier.

2.2.3

TDMA

TDMA isthemain_technologyused

by

the GSMsystems.There isno needtogo

greatexplanation becausethe GSMnetworks have already been coveredin moredetail

comparedto theCDMAnetworks andthe 1st

TDMArefers _actuallytoTime Division Multiple

Access,

whichis aparticular method for_{sending information}overthecommon airinterface. ButthenameTDMA isalso

commonlyusedtoreferto a

family

of mobiletelephone systems.

Considering

thedifferentdefinitions it ispossibleto _saythe

following

abouttheTDMA:

As an airinterface TDMAdividesthe available spectruminto a series of_very

tightly

definedradio_channels, and each channel is divided intotimeslots. Thetime slots are

groupedtogether toform frames. TDMAallows multiple userstosharethesame

radio channel

by

_assigningthedatapackets fromeachconversation toa particular

timeslot.

[3], [11], [14]

Fromthe pointoftheTDMA Based Mobile Phone systems,TDMAmeans abitmore.

Althoughthereare other particular names giventoTDMAbasedsystemssomeof

them, liketheAmericanDigital Cellular

(ADC),

werejustknown asTDMAphones.

Themostknown TDMA mobile phone systems are

IS-54,

and IS-136.

[11]

IS-54,

was thefirstAmericanDigital Cellularsystem. ThepredecessortoIS-54was

theAdvanced Mobile Phone System (AMPS).

AMPS,

is commonlyreferredtoas

analogcellular. In ordertoincreasethenumber of userssupportedin

AMPS,

IS-54

introduced digital voice channels.Through theuseof a vocoderitwaspossibleto

allow _upto three userstosharethesame voice channel. It is importanttonotethatthe

control channelin IS-54was still analog.

IS-136 is

basically

an interim

Standard,

which detailstheexact

functionality

ofthe

by

revisionA. Revision 0 introducedalotof new services andfeatures toAmerican

Digital Cellular. Thesenew_{features include: enhanceduser}

services,_sleepmode,

private systems and enhanced security.

[11]

Somecharacteristics oftheTDMA basedmobile networks and comparison ofthem

insidetheirown_categorycouldbe done asinthe

following

table.

Table. 5:

Characteristics

of

Contemporary

TDMA Systems

*[26]

Bandwidth

(carrier

spacing)

UpstreamSlots

perframe

Percent Payload'

in Time Slot

IS-_{54 48.6Kbps 30 kHz 6.7ms 3 (6with half-rate}

coder) YES 80%

GSM 270.8Kbps 200 kHz 0.577ms 8 (16withhalf-rate_coder) YES 73%

3.

Further

Steps

to

3rd

Generation

:

HSCSD,

GPRS,

EDGE,WAP

Theintermediatestepsbefore

implementing

the3rdgenerationnetworks are_really

importanttothe_operators, if

they

donotliketogive_uptheir_{existing infrastructure but}

followapath of_upgrading transitionally.Mostofthe operatorswouldliketoprotecttheir

currentinvestmentandfollow atransitionalphasefortheimplementation ofthe3rd

generation. The_{organizations,} like

ITU,

_working onthenew standards are aware ofthis

situation_verywellas most oftheirmembers are operatorsand equipment manufacturers.

Thismakes theorganizations sensitive to theneedtoprotectthe investment. Those

intermediate solutions are_already

being

implemented

by

some oftheoperators nowadays

and

they

are

becoming

more importantforallthenetwork operators andtherestofthe

telecommunicationsworld.

[2]

3.1

Why

The Need For

Intermediate

Solutions?

Theconsumeris

looking

beyondthe voice_onlymobileservices now

available. Thereishoweverstill some timebeforethe 3rd

generationmobile networksare

operational. Inaddition theamount ofinvestmentmadeinthe 2ndgeneration networksis

sohuge thatno operator canthrow themaway inone

day

andstart

building

a complete

new 3rd

waytoget useout ofthosenetworksfortheoperatorsandtheconsumers who areboth

focusedto deliverand usedataon an

increasing

scale.

GSM isabletodeliver 9.6 Kbits/secor 14.4_{Kbits/sec bandwidthfor}the datatransfers

today. This isnot enoughformost oftheapplications consumers wouldliketo beableto

usethrough themobile. Thesolutionslike

HSCSD, GPRS,

EDGE,

WAParethe answers

ofthe

industry

until abettersolution arrives (3rdgeneration). Thosetechnologiesmakeit

possibleforthemobile operatorsto

keep

theold network andmake no or_only some

changes andadditions totheirinfrastructureand offer someimproved bandwidthsand

newservicestotheirconsumers.

Afteranewserviceis releasedto consumers_{it usually}takesseveral yearstoreach

a volume of consumers thatcan beseen asthemass market. Becauseofthisreason

operators shouldstart _earlyenoughin the targetmarkets andbusinesses. Operatorsthat

become earlyadopters of mobiledatacangain a significant advantage overtheir

competitors,both interms of customer

loyalty

andin-houseexpertise.This isanother

importantreason forthe operatorstostart with thegenerationjust beforethe 3r

generation (socalledgeneration 2,5).

[17]

3.2

HSCSD (High Speed

Circuit-

Switched

Data)

Theconnectionsusedin thefixednetworksforspeechanddatawereCircuit

exists.It makes senseinthe case of a continuousdata streamtobe transmitted, likethe

video _{transmission, which requires a constantbitrate andtransmissiondelay. The}

HSCSD is still a circuit switcheddata_connection, which occupies severaltimeslots

together, but itwill offer morebandwidthforthe datacustomerswho needthose

bandwidthsnow.

High Speed CircuitSwitchedData

(HSCSD)

wasapproved and specified

by

ETSI

in

February

1997. The HSCSD bitrate, 57.6 Kbit/suncompressed,is comparabletoone

ISDN B-channel.

[17]

HSCSDoffersthemobileoperatorand subscriber anumberof

benefits. Theoperatorbenefits from

HSCSD'

shigher bitrates without

having

toredesign

itsGSMnetwork._{HSCSD is already commercially} available

by

_manyoperators around

theworldbefore General Packet Radio Service (GPRS). Butthemission ofthe HSCSD

willnotbe finisheduntil theGPRS and other enhanced services areintroduced dueto the

factthat thebandwidthofHSCSD isguaranteedandtherewill alwaysbe aneed for

connectionswithguaranteedbandwidth.

[17]

Someexamples of applicationsHSCSD couldbe usefulare:

E-mail downloadand upload.

Bandwidthguaranteedmobilehigh-speedLANaccess.

Filetransfers.

Vertical applications such as batch-typefieldsales infoordocumenttransfer.

Real-timeapplications

demanding

aconstantbitrateandtransmissiondelay.

Mobilevideophony.

[17]

Looking

deeperintohow HSCSD works we needtostart

looking

into_uplink,

downlinkstreams ofthe GSMmobile_{devices.Theuplink anddownlinkoftheGSM}

trafficis handledon_{different frequencies. Butthereisone restrictionHSCSD}

places

upon multipletimeslotlinks andthatis thatthe timeslots allocated mustbe consecutive.

This meansthe standard routineof_{receive,transmit,} monitor a neighbor shouldbeableto

run within an8 timeslotframe. Thismakestheuse of morethan 2channelstogether_very

hard as canbe seen

by

theFigures 10and11 below. When using 3 timeslotsitmight

look like thereis no probleminthefigure but dueto the

timing

advance appliedto the

uplinkthereis aproblem. But thisisthecaseforthesymmetrical use oftheuplinkand

downlinkchannels.

Mobile Rx

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

\

Measure

\

Measure

\

a Neighbour

\

a NfTighbour

Mobile

TX

\

/

\

/

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

2-timeslots

Data Rate : 28.8

Kbit/sec

Mobile Rx

0 1 2 3

\

X

5 6 7 0 1 2 3

I

4 5 6 7

Mobi eT

\

Measure

a Neighbour

Measj/re

a Neighbour

0 1 2 3 5 6 7 0 1 2 3 5 6 7

3-timeslots _a

Figure. 11 : HSCSDwith3 Timeslots

Becauseofthisreason we needtomake substantial hardwarechangesinthemobile

stationifwe wouldliketouse _{symmetrically 3}or more channelsforthe transmission and

reception (uplink-downlink). Butthereisanother solution to this additional hardware

requirement

by

_usingasymmetricaluplink anddownlinkchannels as seen

by

theFigure.

12 below. This ispossiblebecauseoftheusual nature ofthedatatraffic.Ifwe arenot

using

2-way

video or some similartypeofdataservice,usuallythe nature ofthedata

downloads areasymmetrical. This meansthat while wedownloadthingswe_{usually do}

notsendmuchdatato thehostwhile wedownloadthe

data,

butthehostkeeps sending

dataand needs much morebandwidth on onedirection. TCP/IP sessions areusually

typicalexamplesofthis scenario.Mostofthe datatransfergoesfromthehostto the

terminal.

Only

afractionofthe traffic goesintheoppositedirection. In_{this case,usually}

Mobile

Rx

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

\

Measure

\

Measure

\

a Neighbour

\

a Nejgnbour

Mobi

e Tx

\ /

\/

0 1 2 w- 6 7 0 1 2 3

UJ

5 6 7

Asymmetric

4 & 1 Timeslots Rx Data Rate : 57.6 Kbits/sec

Figure. 12: HSCSDwithAsymmetric

4-Rx,

1-Tx Timeslots

Thismeans we canputthe

following

Table. 6togethereasily. Butthe_{reality may look}a

little bit different becauseone

interesting

_point, whichcould causeproblemsforthe

HSCSD,

is thepossibleneedfornew mobiledevices iftheconsumerneedstouse more

than 3 timeslotsonthesametime. This is because ofthereasonthat_upto three

consecutive timeslotsinone framecanbeused

by

mobiledevices with_onlyone

transceiver.Ifmorethan three timeslots aretobe _{used, the}mobiledeviceneeds a

separate receiverformonitoring.Forthis reason, thefirst HSCSDcapable deviceswill

use_{symmetrically 2}channels fortransmitandreceiveor3 forthereceive and 1 for

transmitasymmetrically. Anotherpoint directsto this_{way is}thatifthe mobiledevice

usesmore thanonetransceiverforonetransmissiondirection the amount of_{energy it}will

use will increaseandthe batterieswillbemuch quicker_emptyagain.

HSCSD offersbothtransparentandnon-transparenttypes of service astheanswer

foras_manyapplications aspossible. Transparentbitrates meanHSCSDwill offer

requiring

aconstantbitrate as mentioned above.But forthis purposewe needtomakeit

sure that theused number oftimeslots must alwaysbeavailable. This isnotso_{easy if}the

mobile objectis _movingand_changingcells

continuously

_{becauseweneedto makesure}

that thereis a cleanHandoverthattakesplace andthatthenext cell willhaveenough

timeslots available to

keep

the linkup. Withthenon-transparent servicethereisno such

Handoverproblemifwehave atleastonefreetimeslotin thenext cell. Thenetworkwill

allocatetimeslots _accordingto_{availability,} so onefreetimeslotisenoughto make a

Handoveron a non-transparent connection.In such a casetheconsumerwillhave a

reducedbitrate aftertheHandover but atleastthe linkwillnotbe lost. Butcomparedto

thepacket switchedtechnologiesHSCSDwillloosethelink ifthereis notimeslot

availablein thenextcell.

Table. 6: Bitrates offered

by

Nokia HSCSD implementation

*[17]

1 9.6 Kbit/s 14.4 Kbit/s

2 19.2Kbit/s 28.8Kbit/s

3 28.8 Kbit/s 43.2 Kbit/s

4 38.4Kbit/s 57.6Kbit/s

As canbe seen inthe Figure. 12andTable. 6above,HSCSD allowsdatarates of

upto 57.6 Kbits/sec through theaggregationoffour GSMtraffic channelsinto aHSCSD

configuration. Itrequires_onlyasoftwareupgradeto the_existingnetwork. Thismeans

fullusage of severalGSMtimeslotsboundtogethermakesitsuitableforapplications

such as _{file transfer,}email andLAN-basedaccess.

But,

stillit isnotreal wide-band,and

becauseofthisreasonitmightbe seen

by

some operators as

being

a waste ofinvestment.

[10]

Thebiggest disadvantageoftheHSCSD is thecostto theuser. When a useris using

manychannelsboundtogetherhewill haveto_{pay for}all ofthem together. Becauseof

thatreasontheoperators

implementing

thiskindofnew services needtohave a good

price_policytoattract customers and, ontheother_side,generate enough revenue for

implementing

thenewertechnologies likethe 3rdgeneration. Ofcourse

they

should plan

this service_verywellso thatit does not

totally

usethe_{limited capacity}oftheGSM

networks andleave nothingmorefortheother_customers, who wouldjustliketouse the

voice services.Themainmarket_opportunityofHSCSDis between 1999-2000beforethe

GPRS gets _commercially

introduced,

and_commonlyused.However HSCSD isexpected

tocontinueto serve and growbeyond GPRS.

[17]

3.3

GPRS

(General Packet

Radio

Service)

GPRS is _actuallya set of newGSMbearerservicesthatprovides packet mode

transmissionwithinthePLMN (Public Land Mobile

Network)

and communicates with

theexternalnetworks.

During

theseactivities theuser still willbe abletouse theother

3.3.1

GPRS

Characteristics

GPRS offers a nominaldatarate of 114

Kbps,

withamaximum envisageddata

rate of171.2 Kbps. Itrequires newfunctionalentitiestobe installed inthe_{existing GSM}

network. Asseen intheFigure. 13

below,

thosearethe

Serving

GPRS Support Nodes

(SGSN)

and

Gateway

_{GPRS Support Nodes (GGSN). Its benefitcomesfrom}

being

_a

packet switched service. As we sawabove HSCSD was circuitswitched. GRPS is well

suitedforapplications thatrequirepoint-to-pointtransferof user

data,

including

IP data

andX.25 internetworking.

Besides,

GPRS allows theusertobecharged_accordingto

volume. Thismeans theactualtransmitteddataand notthe timeforwhich theuser

remains online. Thiskindof_accountingmakesitstariffstructure attractivefor

bursty

mobile applicationslike E-commerce. Thepoint weshould notforget isthatGPRS is

onlyan interimsolutiontill the 3rdgeneration wireless networks areimplementedwidely.

[image:50.502.37.439.52.320.2]

Figure. 13 : GPRS SpecificNetwork

Oneofthemain elementsin thefigure aboveisthe

Gateway

GPRSSupport Node

(GGSN). It canbe bestcomparedto_carryingout a similartask to thatofthe

Gateway

MSC and providesthe

functionality

oftheIWFaswehaveseen

by

theGSMnetworks.

Those functions canbe listed as [35]:

DynamicIP address allocation.

TransportLayer_routingprotocols support.

Routing

tablesand address mapping.

Screening.

The

Serving

GPRS Support Nodes

(SGSN)

offers similarfunctionstothatoftheMSC

in aGSMnetwork. Thosefunctionscanbelistedas [35]:

Mobility

management _Registersnew GPRSMobile Stations

(MS)

ontothenetwork

in thatparticular area.

Routing

-Routes datapacketsbetweentheMS'sandGGSN.

Ciphering19

GSMcircuit switchedinteractions.

BSS Queue management.

Datapacket counting.

A moredetailedschema oftheGPRS system canbeseenbelow atthe Figure. 14.

The MSCandVLRareutilizedfor initialregistration and_{contacting GPRS MS's but} are

notneeded when_{routing GPRS data. The HLR holds information} aboutthe subscription

detailsandtheAUC whichis requiredforauthenticationand ciphering. The EIRcanbe

usedfor authenticating MS hardware. There is also extra

functionality

required atthe

BSS,

as seeninthe

figure,

_namelyaPacket Control Unit

(PCU),

whichsupportsthe

packet _{switching between} theBSS andSGSN.

19_Ciphering:a

[image:52.502.31.446.50.379.2]

Figure. 14: GPRSNetwork

GPRS isplannedinphases as with theGSM. InthefirstphaseofGPRS

point-to-point

(PTP),

user

internetworking

for PTP and

TCP/IP,

X.28 from

GGSN,

X.25 from

GGSNtoexternalPDN'saresupportedbutthereisno support plannedforthe realtime

dataapplications whilst onthemove.This is dueto theimplementation ofthe

handovers,

3.3.1.1

Data Rates

Forthedatarates ofGPRS itwas_{already been}proventhattheairinterfacecanbe

increasedto a maximum of22.8 Kbps fromthe 9.6 Kbps. Butthere are4differentdata

ratesoffered. The higher datarates are achieved

basically by

_{using less} errorprotection.

Mostofthetime thiscanbe leftto theapplicationitselfanyway. GPRS utilizes the

differentdatarate options

dynamically

to suittheradioconditions atthe time. Ifhigh

levelsofinterferenceand noise are _{present, the}lowerrates areusedto provideabetter

error protection. Thedatarates ofGPRS are [35]:

CS-1 9.05kbps

CS-2 13.4kbps

CS-3 15.6kbps

CS-4 21.4kbps

Thismeans ifthecomplete 8 timeslotsare usedthe maximumrate willbe: <