lucent wcdma guide

Making W-CDMA simpleA guide to UMTS networks

into W-CDMA but discovered youreallergic to jargon? Our expert guide feeds

you the facts and skips the migraine.

1Making W-CDMA simple

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UMTS represents an incredibleopportunity for the wireless industry.However we cant pretend that thesimultaneous introduction of a newservice environment and unfamiliartechnologies represents anythingother than an enormous challengefor the operator community.

Dealing with the marketimplications of a new and complexservice environment must be theGSM operators first priority. Theyshould not be worrying about thetechnical issues associated withdeploying a spread spectrumtechnology for the first time. Theirconcern should be how best to usethe in-depth understanding theynow have of their customers toeducate the consumer market aboutthe value of new packet services.They should be developingstrategies to convince the enterprisemarket that mobile operators merita significant share of business ITbudgets.

In addition, to leverage maximumvalue from data service portfoliosoperators need to be able to exploitGSMs roaming advantage; theyshould be focusing on negotiatinginterworking agreements with theirmain roaming partners and urgingterminal vendors to adoptminimum option standards thatfacilitate interoperability.

Meanwhile their infrastructurevendor should be taking care ofdeployment challenges.

Making 3G simple

The problem with trustinginfrastructure vendors with thetechnical burden is that few havefield experience of this type ofaccess technology. Commonfeatures of CDMA and W-CDMAlike cell breathing and pilotpollution simply do not appear inTDMA systems like GSM.

Making Communications Simple


Understanding these aspects ofW-CDMA is critical for efficient andtimely deployment. In addition, itsnot enough simply to deliverW-CDMA systems. The newnetworks also need to be optimizedand cost effective.

In fact there are over 200parameters that impactperformance in spread spectrumtechnology. Knowing how to varythose parameters is key to gettinggood performance out of spreadspectrum networks. This is whereLucent has an advantage over allother infrastructure vendors.Lucent wrote the book on spreadspectrum deployment and has builtmore spread spectrum networksthan any other vendor. And all thelessons learned from CDMA arenow being applied to UMTS.

Developing next generationwireless solutions is a challenge forthe entire industry. But thesolution is to ensure 3Gdevelopment is a genuinepartnership between the operatorand the right vendor. Operatorsneed to be able to concentrate onbuilding new markets and securingthe market share critical for successin the new service environment.For this they need a vendor withfield experience of spread spectrumtechnology thats able and willingto shoulder the full deploymentburden.

In short, its up to the vendor tomake the new technology easy foroperators so the latter can get onwith the serious business ofeducating the market about newservices, satisfying the needs ofcustomers and generating newrevenue fast.

We hope Making W-CDMA Simplewill play a small part in bringingthe 3G vision into focus. Ourobjective is to provide thenon-technicians amongst ourcustomers, journalists, analysts andthe financial community with aconcise and accessible overview ofthis important new technology.

The intention is not just to presentthe technical detail but also tomake it clear W-CDMA has thepotential to transform the world tothe same degree second generationwireless technology revolutionizedthe way the world communicates.

No one should underestimate thechallenges that lie ahead. ButLucent Technologies has theresources, skill sets and experienceto turn vision into reality andensure its customers succeed in the3G marketplace.


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Coming to terms with 3G

Like every technical industry thewireless business is littered withconfusing abbreviations andacronyms. In this guide wed like tobe able to do away with themaltogether but its just not possible.Instead well avoid them when wecan and try to make sense of themwherever they occur.

Any attempt to explain W-CDMAmust first tackle a question thatbothers people whether theyre partof the wireless industry or not. IsW-CDMA the same as 3G and doeither or both terms mean the sameas UMTS?

Unfortunately the answerto this very reasonablequery is slightly long-winded but important forunderstanding whatfollows.

First a bit of history.Throughout the 1980s theworlds wireless operators

used second generation (2G) mobiletechnologies to build thefoundations of todays mobilenetworks. All these technologieshave been defined by standardswith complex specifications that inmost cases must be applied rightacross the network. This period ofwireless development wasinnovative and exciting but it soonbecame clear to operators, vendorsand standards bodies that 2Gtechnology had its limitations.

The astonishing growth of theglobal wireless market was one of

the most significanttechnological andcommercial developmentsof the previous century.This is why theInternationalTelecommunicationUnion (ITU) launched anInternational MobileTelecommunications(IMT) initiative known asIMT-2000. The idea was

What is the ITU? The International TelecommunicationsUnion is a United Nationsorganization responsible for co-ordinating global telecommunicationsactivities, particularly in the areas ofstandards setting, radio spectrumallocation and regulation.


to ensure a clearly defined butflexible approach to future wirelesstechnology development that wouldprepare the ground for moreadvanced mobile services.

This was a far-sighted move on thepart of the ITU as it pre-empted thegrowing importance of mobile dataservices to every operatorsbusiness.

Today mobile technology is nolonger just about voice. Literallybillions of short messages (texts) aresent and received every month andsophisticated services like emailon-the-move and picture messagingare beginning to find a market.After a couple of false starts themobile internet era is finally uponus, but once mobile data movesbeyond the transmission of simpletext messages, the speed andcapacity of mobile networksbecome critical issues.

IMT-2000

Back in the early 1990s the ITUanticipated such developments and

IMT-2000 was its vision of the kindof advanced networks needed tohandle enhanced mobile services.

According to the ITU, the definingcharacteristics of IMT-2000 wouldbe: high quality networks, services

and terminals; a high degree of commonality in

design; global roaming capabilities; compatibility of services within

IMT-2000 and fixed networks; multimedia and advanced

data-service capabilities.

At the World Administrative RadioConference (1992) it was decided toallocate radio spectrum globally inthe 2GHz frequency band for whatwould become the IMT-2000 familyof technologies. And because thesetechnologies would supersedesecond generation or 2Gtechnologies they have becomeknown as third generation or 3Gtechnologies.

So the IMT-2000 vision could alsobe described as a 3G vision butwhat were the actual technologies

Today, thecommercialsuccess of earlymobile servicescan be difficult to understand

Definition Whatis IMT-2000?IMT-2000 is ageneral term fortechnologiesplanned to beincluded in theITUs worldstandards forthird generation(3G) mobilecommunication.

5Coming to terms with 3G Making W-CDMA simple

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that would turn this vision intoreality?

This is where the acronyms reallystart to get out of hand. TheEuropean TelecommunicationsStandards Institute (ETSI)developed a set of standards thataddressed the IMT-2000 concept. Itcalled the result the UniversalMobile Telephone Service(UMTS) and later concluded that

the air interface or accesstechnology best suited to deliveringthe UMTS standard would bewideband-CDMA (W-CDMA).

The ITU accepted UMTS as anofficial standard for the realizationof its 3G vision and also agreed twoother main standards CDMA2000and Chinas TD-SCDMA.

So there you have it. 3G is thegeneric term for next generationmobile networks and services;UMTS is ETSIs 3G standarddeveloped within the ITUsIMT-2000 framework; andW-CDMA is the most widelyselected technology designed toturn next generation networks fromvision to reality.

It may not be pretty but it makes akind of sense.

Fact In the interests of completenessits worth mentioning that theGSM Association believes that becauseW-CDMA is the 3G technology ofchoice of the worlds GSM operators, itwould make sense for W-CDMA to beknown as 3GSM. It remains to be seenwhether the rest of the industryadopts this approach.

Fact At last countW-CDMA hadbeen selected by80 per cent ofthe worldsoperators thatintend buildingnext generationnetworks.

Fact Air interfaceor accesstechnology is thepart of wirelessnetworkarchitecture thatprovides the linkbetween a usersphone (or othermobile device)and the corenetwork.

An early versionof the mobilevision, courtesyof Bell Labs


How cellular networks work

When thinking about how mobiletechnologies work, its important tokeep in mind that wirelessspectrum is a very scarcecommodity. And in todays worldscarce means expensive. To put thisin perspective, in the UK andGermany operators paid an averagein excess of US$7billion(e5.7 billion) just for the privilegeof using a chunk of the radiofrequency set aside for 3Gnetworks. This was before theydspent a penny actually building thenetworks.

So the conservation and efficientuse of spectrum is a majorpreoccupation of wireless operatorsand the engineers that designnetworks. Inefficient use ofspectrum means networks carry lesstraffic; less traffic means fewercustomers and a poor return oninvestment.

Network capacity is becoming aserious problem for many

operators, especially in Europe. Infact according to a recent report byanalysts Stearns International,while wireless operators cancontinue to build capacity byadding carriers and other features,ultimately there are limits to howmuch capacity can be added. Thebenefits are also likely to beshort-lived. 2G simply won't beable to keep up with growing voiceand data demands of new mobilephones on the market.

One of the main reasons W-CDMAhas been selected by so manyoperators for 3G networks is that itwill very significantly increase anoperators capacity and help makethe most of the scarce spectrumtheyve been allocated.

To understand the characteristics ofW-CDMA we first need to thinkabout how cellular networks gottheir name.

Rather than using a few extremely


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powerful radio transmitters thatcould provide mobile services to avery limited number of customersover a large area, cellularcommunications divide areas into alarge number of cells served by lesspowerful transmitters andcontrollers called base stations.

This cellular arrangement enablesoperators to reuse their expensivefrequency allocation according tothe number of cells they create ontheir networks. The manner of thatreuse is one of the factors thatdifferentiate the various type ofcellular technology.

The key takeaway here is that acellular approach to network designenables operators to provide moremobile services to more people.

Access technologies

Operators want networktechnology to maximize capacityand guarantee the best possiblestandards of call quality. To a largemeasure, both of these factorsdepend on the amount of spectrumthat has been allocated, the amountof traffic expected on the networkand the way the access or airinterface technology handles callsor data transmissions. There are three main cellular accesstechnologies and each uses radiofrequency in a significantly

different way. The technologies arecalled: frequency division multiple access

(FDMA); time division multiple access

(TDMA); and code division multiple access

(CDMA).

What is FDMA accesstechnology?

In FDMA (Frequency DivisionMultiple Access), each user isassigned a slice (channel) of theavailable radio spectrum for theduration of the call. ConventionalFDMA is used for the firstgeneration of mobile wirelessservices. Without additionalfeatures, it is not an efficient meansof sharing radio spectrum, and it iseasy to see why.

Conventional FDMA splits the radiospectrum into 30kHz channels. In

Fact Analoguecalls aresignificantly lessefficient thandigital calls.Analogue signalsare verysusceptible todistortion, whichis why analoguephones needmuch morepower to achieveacceptable callquality thandigital phones.

What is analogue? Analogue is a transmission method forvoice, video and data using signals (such as electricity orsound waves) that are continuously variable rather thandiscrete units as in digital transmissions. Analogue refers tosignals that can represent an infinite range of numbers (asopposed to digital signals that can only represent distinctwhole numbers). In the context of wireless communications,analogue refers to transmission networks built in the 1980sand that use analogue technology rather than digital.


order to avoid radio interferencebetween subscribers, each cell isallowed only a handful of widelyspaced 30KHz channels that cannotbe re-used by neighboring cells.Since each user requires one 30KHzchannel for the full duration of thecall, this strategy means that thenumber of calls that can be handledby each cell is severely limited.

In other words, conventionalFDMA commits the cardinal sin ofwasting valuable spectrum. It is theleast efficient of todays accesstechnologies.

Because of its rather basic approachto handling calls, as an accesstechnology FDMA has really had itsday. However understanding how itworks makes it easier to grasp thevalue of subsequent developments.

What is TDMA accesstechnology?

As we have seen, in FDMA systemsonly one traffic channel can bepresent on a given frequency in agiven geographic area. This is alsotrue of TDMA systems, but becauseTDMA has been designed to usedigital rather than analoguetransmissions it can be significantlymore efficient than FDMA.

The advantage of TDMA technologyis that it takes a frequency channeland breaks it up into timeslots sothat multiple users can share thatfrequency. In other words, TDMAassigns each call a certain portion oftime on a particular frequency which is why its called Time

Power

Frequencyf1 f2 f3 f4 f5 f6 f7

In FDMA systems, only one traffic channel can be on agiven frequency in a geographic area. In TDMA systems, a frequency is split into timeslots and shared amongmultiple users. In both cases, if the frequency is also beingused by the next cell, the interference will ruin the call.

f6f5

f7f1f4

f2f3

Technical stuffTDMA requiresstrict signallingand timeslotsynchronization.A digital controlchannel providessynchronizationfunctionality aswell as addingvoice mail andmessagenotification.

What is digital? In a digital network, voice is converted to aseries of closely spaced samples that are used to reconstructthe original speech (the original analogue signal) at thereceiver. The samples are encoded in a way that makes themresistant to transmission errors such as signal distortion; forexample, each value can be represented by a series of zeroesand ones. These two possibilities are sufficiently simple andsufficiently different to make it unlikely that fluctuationsincurred in transmission will change the way the informationis interpreted when received; in other words, even a badlydistorted one can still be recognized as a one anddistinguished from a zero. Correct interpretation of all thezeroes and ones allows a full, high-fidelity reconstruction ofspeech. Data (text messages, files, etc) can be transmittedsimilarly.

9How cellular networks work Making W-CDMA simple

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Division Multiple Access. Handsetsand devices using a TDMA networksend bursts of data that arereassembled at the receiving end.

By comparison with FDMAsystems, TDMA technology meansmore calls, more users on thenetwork and better call quality.However there is a limit to thenumber of people that can use thefrequency, depending on the waythe air interface is structured andthat is of course dictated by thestandards. Like FDMA systems, aTDMA system cannot employ the

same frequency in an adjacent cellto one that is already being used.The global system for mobilecommunications (GSM) used byover 1 billion people worldwide isbased on an elaborated version ofTDMA technology.

What is CDMA accesstechnology?

This brings us to CDMA, whichshares many of the characteristics ofW-CDMA and works in a completelydifferent way to FDMA and TDMA.

After digitizing data, CDMA uses atechnique called direct sequencespread spectrum. CDMA takesdata and spreads it across awideband CDMA radio channel.This channel is much wider than wefind in FDMA or TDMA systems;however, a large number of userssimultaneously occupy this samewideband channel. Within thechannel, each user is distinguishedby a unique code.

The wideband signals are resistantto interference, yielding excellent

What is GSM? The global system for mobilecommunications (GSM) is a TDMA-based technology with anelaborated standards platform originally developed for theEuropean market. The GSM implementation of TDMA is nowused by more than one in ten of the worlds population.GSM is used to describe the entire communication systemrather than just the access technology. GSM has evolved toinclude a range of communications platforms that consists ofcircuit switched GSM, general packet radio service (GPRS),enhanced data rates for GSM evolution (EDGE) and 3G GSMthat employs W-CDMA technology (referred to as 3GSM bythe GSM Association).

Technical stuffWhat is directsequence spreadspectrumtechnology?This is a spreadspectrumtechnique usedby W-CDMA thatspreads its signalcontinuouslyover a widefrequency band.The idea is that adata signal at thesending station ismapped into ahigher data ratebit sequenceusing somethingknown as achipping code.The chippingcode introducesprotection thatallows datarecovery ifcertain bit errorsoccur duringtransmission.

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Making W-CDMA simple

call quality in spite of the largenumber of users thatsimultaneously occupy the channel.The ability to share the channelamong many users makes CDMAfar more spectrally efficient thanconventional FDMA or TDMA ie.CDMA can accommodate far moreusers per chunk of radio spectrum.

Another benefit of CDMA is that byusing a very wide radio frequencychannel, CDMA technologyprovides a larger pipe for carryingdata. The result of this is that themaximum achievable data rate overa wideband CDMA frequencychannel is much greater than canbe found on any of the widelydeployed TDMA systems currentlyin use.

From the points of view of bothoperators and their customers,CDMA clearly has a great dealgoing for it. Nevertheless even thisquick overview should show that,in spite of its advantages, theCDMA approach to handling dataand frequencies is considerablymore complex than either of theother systems outlined.

A bit later well look at the mainadvantages and problems associatedwith W-CDMA as an accesstechnology. For the moment, sufficeit to say that if CDMA is complex,then W-CDMA significantly adds tothat complexity.

How is a 3G network organized?

We will be looking more closely atthe benefits and complexities ofCDMA technology when we talkabout the access layer of the 3Gnetwork. For the moment, letsmove on and run through the basicstructure of a mobile network sowe can understand where theaccess layer sits in relation to therest of the network.

As you can see from the diagram,right, a 3G network is made up ofthree main layers.

The access layer is made up ofbase stations (or Node Bs as theyare known in a UMTS network Lucents 3G solution is known asthe Flexent OneBTS) and various radio network controllersthat analyse and control radiotraffic.

The core network has two mainroles. The first deals with directingor routing where voice and data aresent. This essentially means usingswitching systems to routeinformation through a number ofdifferent servers around thenetwork. The second part of thecore is known as the backbone anddeals with such critical functions ashandling access to other packet datanetworks, providing an interface tothe internet and sorting out billinginformation and security.

Technical stuffBandwidthshould not beconfused withthe term band eg, a Samsungphone thatoperates on the900MHz band.Bandwidth isabout the spaceit occupies onthat band. Therelativeimportance ofbandwidth inwirelesscommunicationsis that the size,or bandwidth, of a channel will impacttransmissionspeed. In otherwords, a greatdeal of dataflowing througha narrow channeltakes longer thanthe same amountthrough abroader channel.

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How cellular networks work Making W-CDMA simple

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Finally, the service layer controlsuser preferences and profiles andbasically enables access to theenhanced service portfolios thatmake 3G such an excitingproposition.

Before we move on to look at thecharacteristics of each of these threelayers, a quick word about one ofthe ways in which 3G networksdiffer from 2G networks.

You might remember we explainedthat previous generations ofwireless technologies establishedstandards right across the network.This time around, thestandardization process splits theradio access network and the corenetwork.

The point here is that IMT-2000 hasbeen conceived as a global visionand the idea is that different radiotechnologies should all be able toaccess a common core network. The implication of this radicalstance on standardization is thatalthough different technologies (ie,CDMA2000, TD-SCDMA andW-CDMA) are prevalent in differentparts of the world, this approachenables operators to choose theirown migration path to 3G.

Fact CDMAsignals areencoded using apseudo-randomsequence eachof whichcorresponds to adifferentcommunicationchannel thatthe receiver alsoknows and canuse to decodethe receivedsignal.

Node BNode B

RNC RNC

BTS

BSC

GERAN UTRAN

Applications

Access network

Services andapplications

2G/3Gcore network

Services BearerControl

IP/ATM

GGSNMSC

HLR

SGSN

PDNPSTN

The 3G network comprises three main layers

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There are two main reasons whyGSM operators need to upgrade toW-CDMA.

First while mobile data servicesare crucial to an operators businessmodel, they also consume significantamounts of network resources. Thiscoupled with escalating demand forvoice services means operators needto use a more efficient technologythat helps them make best use ofavailable capacity.

Second many of the customersthat operators expect to use theirnew data services are familiar withsimilar applications over the fixedline internet. This important targetmarket expects mobile technologyto deliver the high data speeds theyhave experienced on their desktopPCs. And they certainly wont paymore for less. For example, researchshows business users expectminimum speeds of 100Kbps beforetheyll commit to using mobile dataon a regular basis. So operators

need networks that can deliver dataspeeds that are considerably fasterthan todays GSM systems can offer.

Even a sophisticated, enhancedtime division technology like GSMcant offer the kind of performancetodays users are starting to demand.However basic GSM can be mademore efficient with the introduction

Packet evolution

What is WAP? Wireless Application Protocol (WAP) is thetechnology that deals with how data content is viewed on amobile device. WAP uses a micro-browser based on a newlanguage called wireless mark-up language (WML) that is aderivative of HTML, the language of the internet. WMLconsumes little in the way of ROM, RAM and CPU resources,which means that even low-end terminals can make use ofWAP.

The advantage of browser technology is that it enables theterminal to decide how to display the information providedby the server. In practice, WAP tailors the informationaccessed from the internet to suit the narrowband bearertechnology and limited display capabilities inherent inwireless communications.

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of packet technology. Its importantto understand the significance of thisapproach to network design becauseit involves a first crucial step on thepath to 3G networks.

Until the arrival of general packetradio service (GPRS) technologyGSM networks had beenbuilt exclusively with whatis known as circuit-switched technology.

The circuit-switchedapproach means that whena call is set up a dedicatedcircuit is establishedbetween caller and called.The drawback with thistechnique is that most ofthe network resourcesassociated with that circuitpath are unavailable toanyone else for theduration of the call. This isfine for voice-centricactivity as there are notmany silent (unused)periods in the course of aconversation. However,circuit-switched technology isunacceptably inefficient for handlingmobile data applications.

Although during a voice call thereare obviously a few quiet periods, ifthe call is being used for data trafficthe typically bursty nature of suchtraffic and the manner in which it isused mean there will be considerable

periods of idle activity. For example,if data has been downloaded from ahost computer to a user eg, whilesurfing the internet the user ofteninteracts with that downloaded databefore responding with other data.

The period between the userreceiving and sending datais idle network time thatcould be used for othernetwork traffic.

By contrast, packet-switching technologyoperates by splitting traffic be it voice or data intoa set of containers calledpackets. These packets arethen transmitted with otherusers packets over acommon circuit before beingseparated and re-assembledat their destinations.

This sharing of resources,along with the ability touse common networkprotocols andinfrastructure, leads to a

more cost-effective transmissionsystem and improved user experience.

Packet technology offers users abetter experience because it allowsthe kind of always-on connectionpeople are used to with desktopinternet usage. Once a connection isinitiated, users have a permanentvirtual link into the network,

What is GPRS? The general packetradio service (GPRS) is the packet dataupgrade for a circuit-switched GSMnetwork. GPRS is known as 2.5G GSMand works by concatenating or joiningtogether multiple speech channels toprovide higher bandwidth dataconnections for GPRS data users. Inother words, although the radiobandwidth remains the same, it isshared between the voice users andthe data users. The network operatorhas the choice of prioritizing one orthe other. The arrival of GPRS alsomeans that for the first time GSM cansupport IP and X.25 capability andaccess a wide range of public andprivate data networks.

Technical stuff A 2G circuit-switched GSMradio accessnetwork istypicallyconnected to themobile switchingcentre (MSC), andthen on to thepublic switchedtelephonenetwork (PSTN).The radio accessnetwork consistsof a number ofbase transceiverstations (BTS)and base stationcontrollers (BSC).Adding GPRSrequires softwareupgrades to thebase stations andBSCs, and theaddition of apacket datanetwork. From a usersperspective,customers needGPRS-capableterminals andPC-interfacecards.

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which therefore responds quicklywhen there is data to be sent.

Because it uses more efficientpacket-switched techniques GPRSoffers faster data speeds than thoseavailable over circuit-switchednetworks which is just as well,because basic GSM can onlymanage data speeds of 9.6Kbps. Inpractical terms, GSM operators withGPRS networks can now deliverdata rates of around 20 to 35Kbpswith some speed bursts dependingon network activity and otherfactors. This is useful as an interimsolution but way short of the 200-400Kbps that users will experienceusing W-CDMA networks.

Like GPRS, W-CDMA uses packetdata techniques that provide analways-on connection to thenetwork but in other respects this

code division system is aconsiderably more sophisticatedtechnology.

Its worth mentioning a challengefacing operators that attempt to runservices over a combination ofW-CDMA and GPRS networks.Many companies are planning toconcentrate W-CDMA in highlypopulated areas in the first instancebefore developing morecomprehensive 3G coverage. Theproblem arises when a customerusing services over a high-speedW-CDMA connection moves into amuch slower GPRS zone.

This hand back issue will oftenmean a significant deterioration ofservice quality and customersexpectations will need to be carefullymanaged until comprehensive 3Gcoverage becomes available.

RememberPacket-switchednetwork: Acommunicationsnetwork thatuses sharedfacilities to routedata packetsfrom and todifferent users.Unlike acircuit-switchednetwork, apacket-switchednetwork doesnot set updedicated circuitsfor each session.

RememberCircuit-switchednetwork: Acommunicationnetwork thatuses a type ofconnection thatestablishes acontinuous linkbetween callingand called usersfor theirexclusive useuntil theconnection isreleased.

BTS BTS

BTS

PSTN

BSS

MSC

Short messagingservice platform

Intelligentnetworking

Gateway mobilelocation centre Voicemail

Application layer

Access layer

BSC

BTS BTS

BTS

PSTN

BSS

MSC

Short messagingservice platform

Intelligentnetworking

Gateway mobilelocation centre Voicemail

Application layer

Access layer

PDN

IP backbonenetwork

GGSN

SGSNBSC

A basic 2G GSM network (left) and a 2.5G GSM/GPRS network

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Having seen how the introductionof always-on packet datatechnology has evolved GSMnetworks, lets move on anddescribe each layer (see diagram,page 16) of a fully evolved UMTS3G network. Well start with theradio access network, which inUMTS networks is also called theUMTS terrestrial radio accessnetwork (UTRAN).

The access network is the part ofthe 3G network that includescustomer access devices likephones, base stations (known asNode Bs in UMTS networks) andradio network controllers (RNCs).

To understand how all this fitstogether, think back on howcellular systems work. Predictablyenough the basic geographic unit ofa cellular system is known as acell. Coverage areas are dividedinto small cells, each of whichcontains a radio ransmitter/receiveror base station. The cells can vary in

size depending on terrain and otherfactors like population density anduser demand.

By controlling the transmissionpower and the frequencies assignedfrom one cell to another, networktechnology transfers (or hands off)calls to other cells and radiofrequencies as users move around.

Base stations are usually the mostconspicuous parts of a mobilenetwork. Youll see them on poles,fixed to high buildings, anywherewith a good elevation above thearea to be covered. A base station issimply a transmission and receptionstation that handles network traffic.Its a collection of software andhardware that usually includes oneor more receive/transmit antenna,microwave dish, and electroniccircuitry.

As the name implies, radio networkcontrollers (RNCs) control the radioelements in a network. This means

The access network

Fact If the accesstechnology or airinterface isregarded as thepipe thatconnects mobiledevices tonetworks, it isthe width ofthis pipe thatdetermines howmuch data can besent and receivedat any givenmoment. Forexample, aW-CDMA pipe is considerablywider than a GSM or cdmaOne pipe.

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the RNC has the overall control ofthe logical resources of its Node Bsand it is also responsible for thehandover decisions (from one cellto another) that require signallingto the users handset or device.

These elements are all critical partsof network architecture. However,its the air interface used in UMTSnetworks that radically impactstheir design and performance.

The air interface

As we have seen, the W-CDMA airinterface is the technology thatconnects the user device to basestations. More precisely, the airinterface specifies the characteristicsof the radio transmission between abase station and mobile device. Itdefines the frequencies or thebandwidth of the radio channels,and the encoding methods used in this case W-CDMAs code divisionscheme.

By now it should be clear thatspread spectrum W-CDMA accesstechnology is significantly morecomplex than that employed in 2Gsystems. This complexity translatesinto increased network costs and itsworth noting that the radio accesslayer of a network will oftenamount to around 70 per cent of anoperators total capital expenditureon network infrastructure.

To keep costs to a minimum itsclearly important to get theplanning and set up of the newnetworks right first time, but theinherent complexities of W-CDMA

Node BNode B

RNC RNC

BTS

BSC

GERAN UTRAN

Applications

Access network


2G/3Gcore network


IP/ATM

GGSNMSC

HLR

SGSN

PDNPSTN

The access layer in the 3G networkFact What is the GERAN? The3GPP release 5specified thesecondgeneration GSM/EDGE radioaccess network(GERAN) that canconnect througha 3G corenetwork througha Iu interface.

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The access network Making W-CDMA simple

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technology dont make it that easy.Previous experience of spreadspectrum technology is certainly apowerful advantage.

But if using W-CDMA makes it sodifficult to plan and roll outnetworks, why not use a differentsystem? The answer comes down toa combination of the technologysefficiencies, the high data speeds onoffer and the advantages andeconomies of scale that kick inwhen a particular approach isadopted by 80 per cent of themarket.

As we have seen, othertechnologies do not allow the use ofa given block of radio frequenciesas efficiently as CDMA-basedsystems. Code division schemeshave been selected for 3G becausethey will allow operators to offerthe most capacity from scarce andexpensive radio spectrum.

On the plus side

Before dealing with the challengespresented by W-CDMA, lets firstconsider the very considerableadvantages of the spread spectrumapproach.

The highly efficient re-use of radiospectrum possible with CDMA-based networks removes therestriction that each cell uses a

fixed, limited number of channels.In fact even W-CDMA users onadjacent cells can all use the samewideband frequency channel.

Because each channel is encodedusing a different spreading code itcan co-exist with many others yetstill be separated when required.In addition, the choice of codes foreach channel is set up in such away that minimizes the co-channelinterference between users,allowing easier recovery of theindividual channels.

The disadvantage of such acomplex scheme is that cellcapacity is not as easily quantifiedas in time division multiplexedsystems like GSM. On a W-CDMAnetwork, determining cell capacityis a calculation dependent on thenumber of concurrent users andthe average level of interferencebetween users. This characteristicmakes the planning andoptimization of W-CDMAnetworks extremely demanding.

The spread spectrum concept usedwithin W-CDMA has certainlyproved its worth in earlier CDMA(ANSI-95) deployments aroundthe world. The technology hascreated very cost-effectivenetworks with high capacities,while at the same timemaintaining a high standard ofvoice quality.

Interference on time divisionnetworks Time division technologieslike GSM divide the available spectruminto narrowband channels that aretime-shared among users. In order tolimit co-channel interference betweenadjacent cells, each cell is restricted tothe use of selected channels. Othercells can only reuse these channels ifthere is a significant distance betweenthe cells in question. Such restrictionslimit each cell to the use of a smallsubset of the available radio spectrum.The major disadvantage of thistechnique is therefore a decrease inradio spectrum efficiency. In addition,handoffs between cells have to behard, since the mobile device mustdrop one distinct radio channel beforeswitching to another (see page 21).

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W-CDMA takes the technology astage further and employs verysimilar core principles tocdmaOne (ANSI-95), but alsoincludes major codingimprovements as well as using awideband carrier. In this way, theW-CDMA standard provides evenmore capacity in a given slice ofradio spectrum than the currentCDMA standard.

The challenges

So what are the extra complexitiesof a W-CDMA solution? Well, thesefall into three main areas: universal re-use of the same

wideband channel increasescapacity in a given bandwidth,but requires that co-channelinterference be properlymanaged;

What is cell breathing? Cell breathing is one of the best-knowncharacteristics of spread spectrumtechnology. Understanding itsimplications offers a good insight intowhy W-CDMA networksare so tough to planand optimize.

Lets consider theuplink, which is thesignal that moves fromthe mobile device to the base station.And lets say you are making a call andtwo other people join you in your celland start using their mobile devices.Because of the way CDMA works, theadditional traffic generated by the otherusers causes increased interference. Thismeans that to maintain your call qualityit is necessary for your mobile device toincrease its power level. And if youincrease your power level, the other pairof users in your cell will also experienceadditional interference. So they can thenup their power levels and Youre right

identifying the operating range in whichyou have stability for your power controlalgorithms is paramount to operating aCDMA system in an efficient manner.

This is where cell breathing comes in tothe story. Lets return to the scenario inwhich multiple users are making calls ina cell and that your mobile device mustincrease its power to maintainperformance. Suppose before the othercallers arrived your mobile device wastransmitting at maximum power level.Since it is impossible for your mobile toincrease its power level, the onlysolution is to get closer to the basestation which of course is impossiblein real time.

So the coverage experienced by mobileusers can vary as other users access anddrop off the system. Which is whyCDMA cells are said to breathe.Addressing this effect via design andcustomized software is an importantpart of W-CDMA planning.

this seems to be moving towardssome kind of infinite loop.

In fact there is a stable range in whichinterference is handled. Certainly at

lower levels of cell loading thesituation is quite

manageable with thepower controlalgorithms that have

been created for CDMA.However, as cell loading becomes

greater, the difference in the power levelfor all of the users must increase. Inother words, as you approach thegreatest possible cell loading, a situationarises in which mobile devices musttransmit infinite power in order toachieve what is called the pole capacity.

Of course, this is impossible becausemobile devices can never transmitinfinite power. Instead, it is necessary toback off the capacity for a given radiochannel until it reaches a manageablelevel. Calculating that level and

19


>>

the gain in usability inherent insoft handover (see page 21)increases the effective cellcoverage area and decreases therequired cell count when traffic islow, but can only be realised ifhandover thresholds are correctlyestablished;

W-CDMA performance isdescribed as interference-limiteddue to the presence of manyencoded but simultaneoustransmissions on the same carrier.Optimum performance demandstight control of transmit powerlevels to minimize interference(just enough is the correctlevel!), which therefore requiresthe use of advanced algorithmsfor fast power control. Variable-rate speech compression isanother feature used to guaranteea high level of voice quality underthese varying conditions.

To understand how all this affectsthe planning and implementationof W-CDMA networks, letsconsider these complexities in alittle more detail.

Capacity planning

The use of a constant number ofnarrowband channels in 2G GSMdictates a fixed cell capacity. Thingsare much less certain in theW-CDMA world.

W-CDMA cell capacity varies witha number of factors. These includethe average level of interferencegenerated by surrounding cells,along with the location, speed oftravel, signal fading and speechpatterns of users. For example, acentral cell in a network canachieve higher-than-average loadswhen the surrounding cells arelightly loaded. This is because sucha situation lowers the averageinterference background that usersin the central cell must combat.

In addition, capacity can be higherfor a universe of users with certaincharacteristics for example, zeromotion, or groupings that aregenerously distributed deep withinthe cell interior (and thereforecloser to the base station). Thisbrings about a condition in whichthe lower transmitted powerneeded per user allows more trafficto be packed within the CDMAwideband channel.

On the other hand, capacity can belower under a variety of otherconditions for example, asituation in which users tend tocluster at cell edges or wheresurrounding cells are highly loaded.

The bottom line here is that effectiveW-CDMA capacity planning requiresa comprehensive understanding ofthe nature and impact of thesefactors on the access network.

Definition Whatis an algorithm?An algorithm isjust a formal andrigorous set ofinstructions orprocedures forsolving aproblem.

Fact Spreadspectrumtechniques arealso used in theglobal positioningsystem (GPS) thathas revolutionizednavigation overland, sea and air.

20


Soft handover capabilities

W-CDMA call handling is morecomplex than GSM because of acharacteristic known as soft handoffor soft handover capability (seeopposite). This is another featurethat, although it makes W-CDMAnetworks more reliable, also makesthem much more difficult to build.

Soft handover allows a singlemobile to be supportedsimultaneously by multiple cells.The result of this is that the linksbetween users and network are lesssusceptible to fading, which in turnenlarges the effective cell coveragearea. In essence, the techniquemeans that the total number of cellsrequired is reduced because eachcell is used more efficiently. The use of soft handover alsomakes the transfer of traffic fromone cell to the next more reliable,because the mobile device entersinto communication with the new(target) cell well before the old(host) cell is dropped.

The benefits of soft handover areclear. But making sure softhandover makes good use ofnetwork resources is criticallydependent on setting handoffthresholds correctly. If thresholdsare too low, soft handover linksthat are not really needed for callsupport will be added. This leads to

increased co-channel interferenceand excessive call processing loads.

If thresholds are set too high, onthe other hand, mobiles that dorequire soft handover links tomaintain voice quality will becompromised.

For cost-effective and efficientW-CDMA network deployment,field experience with soft handoveris essential in the selection ofthresholds that are optimal tonetwork topology, subscriberdistributions and the radiofrequency (RF) environment.

Co-channel interference

With W-CDMA systems, all usersmake use of the same widebandchannel and the result is thateveryone interferes with everyoneelses signals. Co-channelinterference is simply the term thatdescribes the interference betweenmobile terminals on the same oradjacent frequencies.

A key design factor in planning acellular system is to avoid orminimize co-channel interference. With 2G GSM networks co-channelinterference is not a major issuebecause frequency channels areonly re-used within distant cells. InW-CDMA, on the other hand,

Fact Softhandover oftentakes place if amobile device isroughly midwaybetween cells oron the dividingline betweensectors. Thefeature permitscalls to continueeven throughregions wherethe signal fromany one cellwould not bestrong enough tokeep the call up.

21


>

co-channel interference from allsurrounding cells is an intrinsiccharacteristic of the system.Although its part of an approachthat helps to maximize spectrumefficiency and enables soft handover,it must be controlled and minimized.

Although successful strategies formanaging such interference can becomplex, co-channel effects can bereduced by a variety ofoptimization measures. Manysuch techniques have beensuccessfully employed in thecontext of CDMA networks andthey include antenna orientation,cell power adjustments and thecreation of cell-specific informationdownloaded to mobiles.

Field experience of such techniqueswill be essential in the planning anddeployment of efficient W-CDMAnetworks.

Now that weve looked at howtransmissions are handled to andfrom a users handset or device,were going to move on to see how3G networks hook up with othernetworks and services.

Hard and soft handoverLets consider the most challenging problem tackled by anycellular technology a handover of a live call where thesignals are weakest ie, at the boundary between one celland another.

On an FDMA or TDMA network, adjacent cells transmit ondifferent frequencies. As a mobile user in the vicinity of thebase station at cell-1 moves away, towards cell-2, the signalat the mobile device becomes steadily weaker. (The same istrue at the base station of course, where the users signal isreceived.) As the mobile reaches the cells operational edge,the signal strength from cell-1 has dropped to the pointwhere it becomes possible to measure comparable signalstrengths from cell-2. It is in this region that the systemattempts to conduct what is known as a hard handover ofthe call from one cell to another. (And statistically, thisis where the largest number of calls are dropped!)

Fortunately, CDMA technology has many advantagesthat make the handover process considerably moreeffective. Since CDMA can use the same radiofrequency in adjacent cells simultaneously, it is possible for amobile device to communicate with multiple cells at thesame time this enables a much more controlled processknown as a soft handover. This makes it far more likely thatthe mobile will get at least one good signal at anygiven time, thereby greatly increasing the reliability ofthe call as it moves through the handover region.

Soft handover is unique to CDMA networks becausethey utilize two key elements not found in alternativetechnologies allowed use of the same frequency withinadjacent cells, and rake receivers (a radio receptiontechnology building block). The combination of theseelements allows the mobile device to listen to two signals atthe same time, even if they are on the same frequency, andtake the most appropriate action.

Hard handover region

Freq 1

Cell 1

Freq 2

Cell 2

Soft handover region

Freq 1

Freq 1

22


The core network is theintelligence of the mobile system.As youll see from the 3G networkdiagram, right, this part of thenetwork provides the technologythat manages communications withother networks ie, to publicswitched telephone networks(PSTNs) and public data networks(PDNs) and helps organize accessto services and applications. Welllook at how voice and data areactually transported a little later.First well see how the corenetwork is set up.

The work of the core network canbe split into two main areas theswitching and backbone functions.

Switching functions

The switching element of the corenetwork is essential for routing ordirecting voice and data traffic toother parts of the network andbeyond. As we have seen, there are

The W-CDMA core network

3GGGSN

3GMSC

3GSGSN

HLR

Node BNode B

Node B

RNCUTRAN

PSTN

Core

Other UMTSUMSCs

ATM Core

ATM or IPNetwork Backbone

IP Core

PDN

IP

lu

pscs

ATM or IP

3G network overview

23


>>

two different types of switchingused within the mobile world circuit-switched and packet-switched.

Until the arrival of the GPRS dataoverlay, GSM voice networks wereconstructed exclusively withcircuit-switched technology ie,when a call is set up, a dedicatedcircuit is established for the relevantparties. With the growingimportance of data services formobile operators, it was soon clearthe circuit-switched approach wasno longer an efficient use ofnetwork resources.

Packet-switching technologyoperates by splitting data into a setof containers called packets. Thesepackets are then transmitted withother users packets over a common

circuit before being separated andre-assembled at their destinations.This sharing of resources results ina more cost-effective transmissionsystem. This in turn means lowerinstallation and operating costs. Formore detail, see pages 12-14.

Switching functions in the corenetwork are handled by the mobileswitching centre (MSC), whichco-ordinates the routing of callsand connects base stations andmobile devices to other networks.

Within the switching part of anetwork, the ability to offervalue-added, operator specific,differentiated products andservices is made possible by theuse of technology calledapplication programmableinterfaces (APIs).

APIs allow operators to programswitches so they perform avariety of functions that can betailored to the operators targetmarket or existing customer base.This will be of great advantage asthe next generation W-CDMAbased mobile networks are rolledout and greater bandwidth tocustomers will allow feature-rich,multimedia applications to beserved (see pages 31-39).

Another key element of the corenetwork is the home locationregister (HLR). HLRs are databases

WirelessAccess

Gateway

UTRAN

MSC Feature Server

IPswitch

MediaServer

TrunkAccess

Gateway

Bearer plane

Control plane

PSTN

Logical architecture of MSC solution

Lucent FlexentMSC

24


to which subscriber identity isassigned for record and billingpurposes. It includes subscriberinformation such as directorynumber, electronic serial number ofthe subscribers equipment, and theservices/features the subscriber isassigned.

Backbone functions

Because todays networks now needto handle a cocktail of voice, mobiledata and multimedia applications,the backbone of the mobileinfrastructure needs to keep pacewith demands from other parts ofthe network. The move to packettechnology has already had asignificant impact on networkarchitecture.

Some of the main networkelements affected by the packetrevolution are the GPRS supportnodes (GSNs). Although as its nameimplies the GSN was invented for2.5G networks, it will also beimplemented in next generationnetworks. In the move to 3G,however, this part of infrastructuretechnology will undergo significantupgrades.

There are two types of GSN withinthe core network a gateway GSN(GGSN) and a serving GSN (SGSN).The GGSN looks after connectionsto other networks; the SGSN is

responsible for what is known asmobility management.The main function of a GGSN is toprovide the interface between themobile network and other externalpacket data networks forexample, the internet, corporateintranets and other wirelessnetwork domains. The GGSN alsomanages the routing of data packetsto the appropriate SGSN andcollates billing information for thecharging gateway.

The GGSN works by converting theGPRS packets coming from theSGSN into the appropriate packetdata protocol (PDP) format (forexample, internet protocol or X.25)and sends them out on thecorresponding packet data network.In the other direction, PDPaddresses of incoming data packetsare converted to the GSM addressof the destination user. There-addressed packets are sent to theresponsible SGSN. For this purpose,the GGSN stores the current SGSNaddress of the user and his or herprofile in its location register.

One (or more) GGSN may beprovided to support multipleSGSNs.

The SGSN can be viewed as apacket-switched mobile switchingcentre. The main role of the SGSNis to provide mobility management.This is an essential core network

Technical stuffWhat is X.25?X.25 is an earlystandard protocolfor packet-switched datanetworks thatspecifies theinterfacesbetween dataterminalequipment andthe packet-switchednetwork, andhow data isassembled intopackets.

25

The W-CDMA core network Making W-CDMA simple

>>

function because it ensuresthat the mobile user is able touse the wireless networkwherever they are located. Thefirst thing that happens whena mobile user turns on his or

her mobile device is that itsregistered to the nearest orstrongest base transceiver station(BTS). This will happen regardlessof which operator owns thenetwork from which the user iscalling. The BTS thencommunicates with the operatorsnetwork via the SGSN. The SGSNensures the network recognizes theuser, updates their location orrouting table so the network willknow how to contact that user and provides the user with updatedinformation about the services thatare available.

SGSN functionality is essential forthe operation of the wirelessnetwork. However, it is also criticalfor people who want to use servicesand applications that depend on thenetwork knowing where that useris located. For example, location

based services (LBS) is a generalname given to a range ofapplications and services that offerlocation-specific services to a mobileuser.

An inherent functionality of thecellular network is that it alwaysknows the location of everyterminal within its coverage. Untilrecently, this capability had notbeen fully exploited but now thereis growing interest in using suchinformation to develop locationbased services. These could be assimple as knowing the location ofthe nearest hotel or restaurant, ormore critically knowing where theuser is located in case of emergency.

There are a number of technologiessuch as GPS that can locate aparticular handset with an accuracyof a few metres. However, theCell ID technology which isalready part of the GSM networkwill locate a user in a city centre forexample, with an accuracy of a fewhundred metres, sufficient for allbut the most demanding

Lucent FlexentOneBTSMacrocell (indoor variant)

26


application. All phones are able towork with Cell ID whereas withother location technologies therewould be a need to build up apopulation of suitably enabledphones before services could belaunched.

The first wave of location basedservices might include services thathelp businesses keep track of fieldworkers and find a friend typeofferings where users can see if anypersonal friends or work colleaguesare within their immediategeographical area. Otherapplications could offer Yellow Pagestype information predicated on theusers location. Theres no doubtlocation based services offertremendous potential forinnovation and the prospect of newrevenue streams for operators. Infact, a recent report by In-Stat/MDRpredicts that by 2006 the totaladdressable market for LBS will top1.3 billion subscribers.

Finally, the SGSN also controlswhat is known as sessionmanagement. Like LBS, this isanother general term thatencompasses many essential aspectsof the operation of a mobilenetwork and one of the mostimportant of these concerns issecurity. Security is a criticalconsideration for operators andusers alike and the SGSN isimportant in this context because it

helps control access to networkresources. Those who do not haveaccess rights to the network as awhole or to specific applicationsand services are identified as partof SGSN operations. The SGSNperforms authentication and ciphersetting procedures based on thesame algorithms, keys, and criteriaas in existing GSM. GPRS uses aciphering algorithm optimized forpacket data transmission.

Transport technology inW-CDMA networks

The move to 3G means faster datarates and increasingly sophisticatedservices and applications for

IP

ATM

SDHDWDM

GGSN

MSC

DNS, DHCP andFirewall

HLRRNC

SGSN

Netw

ork

man

ag

em

en

t via

IP

Core network protocol

Fact Enhancedobserved timedifference E-OTDis an alternativelocationtechnology thatworks bycomparing timedifferencesbetween signalsreceived at theusers handsetand a fixedmeasuring pointknown as thelocationmeasurementunit.

27


>>

customers. But this comes at theprice of additional capacity requiredin the core network and greatercomplexity in the transportsolutions. Lets see what this meansin practice.

There are many diverse elementsthat make up the transport elementof next generation wirelessnetworks. However, for the purposeof this overview we will considerjust three distinct types IP, ATM,optical and microwave.

Strictly speaking these distinctionsare not technically accurate. For astart, IP and ATM are bothprotocols, while optical andmicrowave provide genericcommunications links. However,this simplified approach makes theirrole in the transport story mucheasier to explain.

It should be clear that theintroduction of W-CDMA basednetworks means a big change inboth architecture and elements.Many network elements will eitherbe introduced into theinfrastructure or evolved to providecompatibility for the nextgeneration networks, applicationsand services.

The arrival of packet technology(see pages 12-14), heralds theintroduction of: packet-switching and

internet protocol (IP) into thenetwork operational layer.

Packet-switching technology hasbeen adopted by the entiretelecommunications industry as thefuture of voice and datacommunications. As we have seen,unlike circuit-switching solutionspacket switching means that voiceand data traffic is bundled intostandard IP packets and distributedacross a standard, harmonizedinfrastructure.

Internet protocol

Using an industry-standard protocollike IP means that the infrastructurethat supports the wireless networkis cost-effective to build. This isbecause a network that uses thisstandard only needs one type of

What is IP? Internet protocols were first developed in themid-1970s when the Defense Advanced Research ProjectsAgency (DARPA) started looking for ways to establish apacket-switched network to facilitate communicationbetween dissimilar computer systems.

The Internet Protocol (IP) is a network layer protocol thatcontains addressing information and some controlinformation so that packets can be routed. There are twodistinct parts to IP. Input extracts the data payload from adatagram, processes header information and takes theappropriate action. Output encapsulates transport layersegments, multiplexes higher level input streams andcompiles header information based on payload.

28


router, switch and firewall ie, onethat supports IP.

Another major benefit of using IP isthat the development communityhas already adopted IP as itsstandard protocol. IP is the protocolon which the internet has beenbuilt and it is IP that makesdifferent sorts of databases, billingengines and bespoke applicationscompatible with one another.

It is the convergence of wirelessand the internet where thestandardization of IP has had mostbenefit. When the internet wasconceived and developed, itrequired specific types of IP-basedservers and services to ensure itworked correctly. Now with thearrival of the mobile internet thesesame products can be adapted withlittle or no redevelopment. Productsthat are common to both worldsinclude domain name servers,dynamic host configurationprotocol servers, caching servers,firewalls and internet routers.

All these products were developedto be used in IP-based networksbefore the emergence of the mobileinternet and are now ready for thenext generation wireless networks.Such familiarity speeds updevelopment timelines and savesmoney.

Other IP-based network elements

include the GGSN, SGSN (see pages24-25), and network managementservices that are IP-based rightacross the network.

Asynchronous transfer mode

Another existingtechnology thathas beenadopted by thewirelesscommunity isasynchronoustransfer mode(ATM). Like IP,ATM technologyhas been used in the widercommunicationsenvironment formany years.However, it hasonly recentlybeen associatedwith wirelessnetworks and isincluded in the3G standardspecifications asthe preferred method ofconnectivity between variousnetwork elements.

ATM has been proposed for use onthe lu interface, which is used toconnect the radio access networkwith the core network. It also maybe used on the Gn interface which

What is ATM? Asynchronous transfermode (ATM) is a cell-orientedswitching and multiplexing technologythat employs fixed length packets tocarry different types of data traffic forlocal-area and wide-area networks.Call data is broken up into 53-bytecells in order to multiplex it with othercalls; this increases overall linkefficiency. As a result, ATM facilitatesflexible allocation of availablebandwidth for data, voice, images andvideo. The technologys scalablearchitecture means it is easy toupgrade; it allows a virtually unlimitednumber of users to have dedicated,high-speed connections with highperformance network servers.

Defininition An IP address is aunique 32-bitnumber specifiedas four 8-bitnumbers(represented asintegers), calledoctets. Thenumbers must be in the range0-255. Users areassigned an IPaddress whenthey access theinternet and itserves to identifythe computer ordevice on aTCP/IP network.An example of a IP address is1.163.10.220.

29


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provides connection to otherGGSNs and SSGNs for wide areanetworking. ATM is also importantbecause it can offer virtual privatenetworks to 3G enterpriseend-users, providing securetunnelling of wireless trafficbetween two or more points. In thiscontext, ATM can be used for eithervoice or data VPNs.

There are many key networkelements within W-CDMAnetworks that rely on ATM forconnectivity. They include thehome location register, the mobileswitching centre, the radio networkcontroller and the base stationtransceiver. As with IP, ATMproducts are standard networkingelements and require little or nore-development to be used in awireless environment.

Optical and microwave

The sort of technology crossoverweve seen with IP and ATM alsorelates to optical and microwaveproducts. These traditionally high-speed, high-bandwidth technologieshave long been used in specialistenvironments and applications butnow they are appearing as bearerservices for the next generationwireless networks.

What are virtual private networks?As well as the core functions we haveidentified there are specific applicationsthat are closely associated with, andwork alongside, core networkfunctionality. One such application is theability to offer virtual private networks(VPNs).

The use of VPNs is not new within thewider network arena. However, the useof wireless VPNs within the mobilesector has been brought about by theincrease of bandwidth that will beavailable to the end-user with theintroduction of W-CDMA basednetworks. Extra bandwidth means thearrival of mobile office applications andwireless VPNs have the ability to extendthe reach of corporate networks beyondthe constraints of fixed networks.

Just as wireline enterprises have beenable to leverage the value proposition of

a VPN for voice communications ie, enabling remote users to link tovoicemail and forwarded messages wireless VPNs facilitate database access,messaging and provide least-costrouting across wireless and traditionalwireline transport infrastructures.

Today, increasingly, mobile workforcesand the growth in the use of laptopsand handheld devices are driving theuse of wireless VPNs. Within mostcorporate environments, wireless datahas been positioned as an isolatedtechnology, independent of existingnetworked systems.

However, increased bandwidth coupledwith the standardization of internetprotocol (IP) as a transport mechanismthroughout the internet, data andmobile industries, wireless VPNs start to become a reality for both voice, byusing Voice over IP (VoIP) and data.

30


If next generation wirelesscustomers are to reap the fullbenefits of the 384Kbps bandwidthdelivered to their mobile devices as opposed to currently 9.6Kbpsavailable with 2G then operatorsneed to offer customers new, higherlevels of service quality. This iswhere optical and microwavetechnologies come into their own.

Although its possible to simulatespeed gains through cached dataand with greater use ofcompression technologies,ultimately it is the deliverymechanism that makes a significantdifference. In this context opticaland microwave products are usedbecause they are reliable, fast andvery efficient ways of deliveringhigh bandwidth connectivity.

Another important advantage ofthese technologies is their ability tooffer bandwidth-on-demand.This is important, for example,when the network needs to provideadditional resources to a cell thatmay be temporarily overloaded dueto a sudden increase in traffic. Oncethe load on the cell decreases and itreverts to its normal loadconditions, the additionalbandwidth that served that cell canbe utilized elsewhere.

Having looked at the intelligence ofthe 3G network, were now goingto consider the applications andservices that will create newrevenues for W-CDMA operators.

What is Voice over IP? VoIP is voice that is transportedapplying the same techniques that are used in thetransportation of data traffic. What this means in practice isthat voice traffic, which traditionally used circuit-switchingtechnology from source to destination, is transported in IPdata packets, and sent to a recipient using the samenetworks and infrastructure as data traffic. As with non-voicedata, the data packets containing voice are re-assembled andplayed to the recipient.

By using VoIP, savings can be made by utilizing the same IPinfrastructure as used by data traffic, thus presenting ascalable cost-efficient network scenario for an operator. VoIPhas been specified by the 3GPP working group for use inW-CDMA networks.

Fact The 3rdGenerationPartnershipProject (3GPP) isa co-operation of standardsorganizations(ARIB, CWTS,ETSI, T1, TTA andTTC) throughoutthe world that isdeveloping thetechnicalspecifications for IMT-2000.

31


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The third layer of the 3G networkdiagram represents the enhancedservice and application portfoliosfrom which operators will generatenew revenues in the months andyears ahead.

The big question now facingW-CDMA operators is what servicesto offer to maximize revenuefrom their new networks. Its worthremembering only greenfieldoperators will move straight to aW-CDMA network. Incumbentoperators will have migrated to 3Gfrom basic 2G and 2.5G GPRSnetworks. This means that by thetime they begin to roll out theirW-CDMA networks, many GSMoperators will have already offereda limited range of data services,some over packet networks.

So the question about what servicesmight be depicted in theapplications layer is really moreabout the evolution of acomprehensive service strategy.

After the usual device challengesand technical delays that have heldup much W-CDMA rollout to date,a number of commentators havestarted to question whether 3Gdeferment is really such a problem.Since the firstwave ofenhanced dataservices isalready up andrunning, theyargue, does thewireless industryreally need 3GW-CDMA rightnow?

UMTS drivers

The answer is an unqualified Yes!And to see why we should forgetabout operators licence rolloutcommitments for the moment andfocus on the commercialimperatives that drive the 3Gbusiness case.

W-CDMA applications and services

No other standard comes

close to the speeds and

capacity offered by 3GSM

underpinned by W-CDMA.

Rob Conway, CEO, GSM Association

32


This means going back to basics.What were the original drivers forUMTS development? Those withlong memories will recall that fromthe start IMT-2000 was always asmuch about network capacity asany specific service proposition.This particular detail seems to havebeen lost in the pursuit of killerapplications. In fact for a while iteven became fashionable to arguethat few 2.5G services come close tothreatening the capacity of existingnetworks.

This is not actually true.

Even relatively simple data serviceslike picture messaging or any formof MMS require network overlaysthat consume a significant amountof network resources. Remember:many GSM operators are betting onthese services to rescue averagerevenue per user (APRU) decline inconsumer markets, so mass markettake-up is imperative. This is whythe GSM Association, most analystsand growing numbers of networkengineers now agree that as morepeople start using these services,

Node BNode B

RNC RNC

BTS

BSC

GERAN UTRAN

Applications

Access network


2G/3Gcore network


IP/ATM

GGSNMSC

HLR

SGSN

PDNPSTN

The applications and services layer in the 3G network

We need to get people used to using data applications. We aregoing down the path of promoting applications that are excitingand which work better if theres more bandwidth.

Nikesh Arora, T-Mobile

33

W-CDMA applications and services Making W-CDMA simple

>>

the strain on 2G network capacitywill very soon become acute formany GSM operators.

Under these circumstances thecrunch question for operatorsbecomes: Do I put in more 2Gradios to extend GPRS services ordo I actually switch these serviceson to a W-CDMA network?

Rather than running to stand stillwith GPRS, it makes more senseto move forward with UMTS.

And as we have seen, one of themain reasons W-CDMA wasselected by the ITU for 3Gnetworks is that this spreadspectrum technology willsignificantly increase an operatorscapacity and help make the mostof the valuable spectrum theyvebeen allocated.

So dull, unglamorous butessential capacity will be one ofthe main drivers for UMTS.Another will be the commercialneed to enhance user experiencefor consumer services.

Operators are developing simplemobile data services over GPRS atthe same time as cable andbroadband take-up is finallyescalating in many key markets.GPRS simply cant deliver theperformance that the target marketfor mobile data has already startedto demand. Mobile service offeringshave to match what consumers willincreasingly come to consider thenorm for consumer applications.

Offering these services or enhancedversions of them over W-CDMAwill be about improving the userexperience and continuing to drivetake-up by matching desktopexperience over mobile.

However, the need to resolve issuesthat include market education,interworking and deviceinteroperability means that GSMoperators cant rely on theconsumer market to drive newrevenues at the speed theinvestment community is likely todemand. So the question is how dowe take current market conditionsand develop a business model that

While 2003 saw MMS terminals become a mass-market phenomenon in some markets, lowpenetration of terminals with integrated cameras prevented person-to-person MMS from becoming a mass-market service. MMS is fuelled by content and this needs to be generated either by usersthemselves with camera phones, or by operators or other third-party players. Analysts Northstream

Definition What is MMS?Multimediamessagingservice is similarto short messageservice (SMS),but in addition totext contentMMS can containimages, graphics,voice, and audioclips. MMSstandards aredefined by 3GPPand the openmobile alliance(OMA).

34


integrates voice and data andenables operators to diversify theirexisting revenue base? What willdrive UMTS revenues right now?

The enterprise market

Lucents research makes it clear thatmobile professionals represent ahuge untapped marketopportunity for GSM operators but as well see, its an opportunitythat can only be addressed via 3Gnetworks.

The arguments for such anapproach arequitestraightforward.First, theres realdemonstrablepent-updemand.Second, there isan actual end-user pool thatdoesnt neededucating.Business peopleknow they needhigh-speed dataon the moveand they knowhow to use theapplications.Why? Because

the applications in question are nodifferent from the ones they usetoday on their laptops.

By focusing on the enterprise spaceUMTS operators can launch 3Gwith a huge advantage: they dontneed to convince users about thevalue of the product. Mobileprofessionals know they needremote access to corporate datawith high levels of security. Andtheir companies dont take too longto recognize that theres verysignificant productivity gains fromaddressing the access requirementsof a mobile workforce.

But from an operators perspective,the value of winning market sharein the enterprise space is wellestablished. While today 20 percent of an operators subscriberscome from the enterprise sector, inmany cases somewhere between 40and 60 per cent of actual profitcomes from this segment.Furthermore, enterprises are loyal churn is lower with businesscustomers.

Finally, launching high-speed datato enterprises gets around theproblems relating to handsetavailability. The target marketalready has laptops and PDAs they just need PCMCIA cards toturn them into 3G devices.

But why take a chance? Why notsit back and see how the 2.5Gmarket pans out? Well, Lucentbelieve theres real first-moveradvantage for operators that get

Fact Wireless telematics areapplications that involve a wirelessexchange of data between people,systems and devices. The introductionof packet data moves cellularcommunications away from beingexclusively person-to-person. Packetdata enables machine to machine andman to machine communicationsusing just a few bits of packet data.Some potential applications currentlybeing developed include vendingmachine communications, vehicletelematics and remote appliancecontrol.

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into the enterprise space ahead ofthe crowd.

And, if you want to attractsignificant numbers of enterprisecustomers 2.5G data speeds justarent good enough. Theressufficient independent research outthere to show that businesses aredemanding 100Kbps in Europe and64Kbps in North America as a

minimum throughput speed.Anything less is not a seriousoption. Were not talking aboutpeak 3G speeds here just theminimum speeds that the enterprise

market demands as a prerequisitefor adoption.

Lets be clear about the kind ofsectors were talking about. In thestudies Lucent has carried out, therehas been very significant interestfrom groups like real estate agents,financial services people, insuranceagents, the health care industry andall types of road warriors prettymuch any place where mobility iscritical to the business model. Theseare very valuable, lucrative marketsthat provide access to new revenuestreams.

To date, most operators haventmanaged to access corporate ITbudgets. So these are customerstheyll want to capture and keep.But be warned its important to befirst or second into this market orrisk losing market share for theforeseeable future.

Accessing the enterprise marketwith UMTS is all about choosingthe right partner. So another keydriver for UMTS success will be foroperators to partner the right

Visiongain believes that superior content will be one of the main reasons thatsubscribers will switch to 3G networks. In time it will be one of the reasons thatsubscribers switch between 3G operators. Once 3G markets mature, the retentionof subscribers in 3G networks will be determined by the quality and range ofcontent and services provided by the operator. Analysts Visiongain

In the report Top Five Mobile and Wireless Technologies forBusiness, Deloitte Consulting identified PDAs as one of thetechnologies that corporations need to deploy to enhanceproductivity and return on investment in the years ahead.The authors maintain that the mobile-enabled PDA hasrecently emerged as an elegant, efficient, integrated devicethat will be a major conduit for mobile data applications.They note that a significant benefit of PDAs is that they makemobile data applications easier to use than on a standardmobile phone interface. This in turn enhances theproductivity and effectiveness of the mobile workforce.

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vendors and integrators that canfacilitate access to large enterprisesand the accompanying newrevenue streams.

The need to increase network speedand capacity for data services plusuntapped potential in the enterprisespace are two key drivers for UMTSoperators. But how can operatorsaccess the mass consumer marketsthat will ultimately determine thelong term success of 3G? Beyondvariants on messaging applications,what are the services that will drivesignificant consumer usage?

The consumer market

The problem here is that theres nosuch thing as a single consumermarket but a diversity of marketsegments that are often tough toreach and predict. Initially theanswer might once again lie inleveraging success in the enterprisespace.

Penetrating the enterprise marketin the first instance allows operators

to engage mobile professionals whoare also target consumer users.Lucents recent consumer researchshows that a significant proportionare attracted by a remote accessservice, allowing them to accesstheir companys network. Thosemost interested are a segment calledcharacterized as convenienceseekers.

Convenience seekers havedeveloped purchasing patternsdriven by the desire to make theirlives simpler, often with the help oftechnology theyve become familiarwith at work. These consumersseek security, speed and control. Asthis segment is driven more byneeds than by wants, it is likely thatsuch people will be early adoptersof 3G provided it provides high-speed internet/intranet access froma variety of locations. The initialrevenue potential from this group issignificant as they are willing to paythe price for remote access,although they are less likely tomove on and adopt a wide range ofadditional mobile services.So convenience seekers could

I find it impossible to believe a service like m-commerce wont be successful. Just think about micro-payments the ability to pay parking costs, taxi fares, theatre tickets and small change transactionsvia a mobile device. Once this service begins to be adopted and universally available I think it willbe one of these things that well ask ourselves how we did without it. In terms of investment anddevelopment, it does take a leap of faith and I think this is why its taken so long to get there.

Bill Best, CTO, GSM Association

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represent the first trickle-downfrom enterprise to consumermarket. But how should operatorsdevelop mass-market servicestrategies from a core business ofenterprise customers?

Lucents extensive two yearresearch programme paints apicture of the consumer market forthe main ten UMTS services. Theseservice concepts were developedusing consumer inputs from focusgroups:

Finding places on the move Voice control Mobile phone replaces fixed line Personal organizer Video-clip messaging News, sports, leisure clips on

demand Video-clip alerts for news, sports,

leisure Remote access to company

network Gaming Gambling

Control, privacy and reliability werethe essential prerequisites

consumers identified before theywould consider a 3G solution.

By conducting follow-onquantitative research in tencountries Lucent has produced afull mass-market segmentation,with a detailed understanding ofneeds and demographics.

After convenience seekers, the nextimportant consumer target could bedescribed as internet lovers. Theseconsumers are less involved withaccessing intranets and tend to usethe internet more for generalinformation gathering andentertainment.

This is a group that places a highvalue on facilitation. Internet loverswill be attracted to the possibilitiesof improved time management andproducts and services that can domore to help them organize theirlives. While members of thissegment are not completely needdriven, they do express manycharacteristics that make them anattractive target for 3G. This groupis technology savvy and will find

UMTS capabilities offer significant benefits totodays so-called road warriors business peopleon the move who want access to office files anddatabases anytime, anywhere. UMTS Forum

Fact A 2003survey* foundthat 32 per centof wireless usersand 38 per centof wirelessinternet userswere willing topay a monthlyfee for locationbased services.The majority ofthose willing topay would spendup to US$5 toUS$10 per monthto receive suchservices, on topof normalmonthly servicechanges.

*In-Stat/MDR

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services such as finding places andpersonal organizer appealing.

Given the high levels ofweb-browsing usage, there isstrong revenue potential from theinternet lover segment as their 3Gactivity levels are likely to be high.In addition, they show stronginterest in the value-added servicesthat replicate the services currentlyavailable today via a fixed internetconnection finding places on themove, video-clip messaging andvideo-clip alerts/on demand.

The communicators segmentshould be considered next asmaintaining and developing voicerevenues is an important strand ofthe 3G business case. The ability tooffer low-cost voice means thatfixed line revenues can be attacked both domestic and PBXoriginated.

Communicators are a group thatuses the internet frequently, butthese consumers are more limitedin their internet locations, relyingprimarily on home access for

internet usage. However,communicators travel away fromtheir home/office frequently andshow a need to stay in touch,taking their PDAs with them whenon the road.

Like convenience seekers,communicators believe newfeatures and technologies will helpsimplify their lives. This is asegment of users that appearalmost desperate in their search forbetter communications solutionsand thus have very high interest infeatures that appear to meet theirneeds. In particular, 95 per centwould like to see their mobilephone completely replace theexisting fixed line. They also havevery high interest in findingplaces, voice control, andpersonal organizer.

Our final segment can becharacterised as fun lovers. This isthe group that will in the firstinstance be avid picture-messageusers and who will go on to beattracted to products and servicesthat are exciting, flashy and

Ideally people will buy just one device that willprovide total seamless mobile access to the office.

Chris Friel, GSM Association

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innovative. They can be temptedby a wide variety of entertainmentand fun services such as video-clipsand gambling. However for themost part take-up will bepredicated on low cost. Since thesegment is also a small one, in theshort term the revenue potentialfrom this group is not significant,but they can be targeted to provideincremental revenue, once thenetwork is well established andnew revenue streams are required.

The take away here is that to winover the consumer market,operators should start withconvenience applications andfollow up with fun applications.Needs not wants will drive theadoption of 3G technology in thissector.

Making it happen

It should be clear that to kick-startthe new revenues required tomake 3G a success, operators needto focus on secure mobile datasolutions for the enterprise. This is

an easier sell than attempting toaddress fragmented consumersegments. Data cards can be usedto launch the technology. Roll outwill be more concentrated, startingwith a small number of largeenterprises with large mobileworkforces. These organizationshave a high willingness to pay forproducts that enhance workforceproductivity, generate revenue andincrease customer satisfaction.

The enterprise market is awaiting asolution UMTS can deliver today.

In the past, the wireless industryhas tended to create technology inthe hope that someone,somewhere might want it. Thistime around the demand for high-speed data has built up in themarket mostly as a result ofchanges in the internet world andin social and working practices while the industry has busied itselfwith interim solutions.

Key drivers are already in place forUMTS success. Now its up to thewireless industry to deliver.

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The adoption into the UMTSstandard of W-CDMA radio accesstechnology has created a solutionthat promises operators enormousscope for the development of new,high bandwidth applications andservices, not to mention hugeefficiencies.

In order fully to realize thosebenefits, however, acomprehensive understandingof CDMA technology is crucial. Aswe have seen, experience in thisfield goes back to the early days ofCDMA, with the deployment andoptimization of IS95, the secondgeneration of CDMA systems. ForLucent this laid the foundationsfor the companys understandingof the characteristics of spreadspectrum technology. Thecompany installed and tested IS95more widely than any othervendor in the world, and wasresponsible for a very largeproportion of the entire globaldeployment of the technology.

Today that experience is beingfurther extended. Lucent hasrolled out spread spectrumnetworks in Europe, Asia, and theAmericas, including 90,000CDMA base stations (morethan one third of the globaldeployed base), more than half ofwhich have the 3G featuresactivated. Almost thirty customersare already using, or havecontracted to deploy, LucentsCDMA2000-1X systems.

These are more than justinteresting statistics, however.This experience is feedingthrough into Lucents W-CDMAactivities, impacting its range ofproducts for the W-CDMAmarket, influencing the way thecompany deploys UMTS, andenhancing the optimization toolsit uses in the process.

Lucent after all, has 340 trainedspread spectrum engineers,many with UMTS experience.

Experience pays dividends

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Optimizing networks

The common features of CDMAand W-CDMA, which includecharacteristics of behavior in spreadspectrum networks such as cellbreathing and pilot pollution, donot appear in technologies such asGSM. Understanding these aspectsof the technology is critical forefficient cost-effectivedeployment.

Lucents suite of CDMAoptimization tools has beenmodified and enhanced forW-CDMA networks. This suite canbe used throughout the design andoptimization process forpre-optimization of the RF network;initial optimization for installingand integrating sites; and forongoing analysis of network data,identifying trends and troubleshooting to maintain networkquality and

lucent wcdma guide

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