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Third-generation TDMAChristofer Lindheimer, Sara Mazur, Johan Moino and Magnus WaleijBy adopting a common radio-access standard and a common core datanetworkstandard, TDMA and GSM systems can share a common solutionfor third-generation networks.The standardization of the first phase of EDGE is presently about to befinalized in the ETSI Special Mobile Group. Phase I of EDGE includes supportfor best-effort packet-data services with high data rates. Phase II,targeted for the end of 2000, will comprise support for real-time applications.Compared to present-day data services in GSM and TDMA systems,EDGE will provide significantly higher user bit rates and spectralefficiency. It can be introduced smoothly into these systems in existingfrequency bands, reusing the cell planning of previously deployed networks.In this article, the authors describe the concepts for introducing EDGEinto TDMA systems, and address performance issues by means of systemsimulations.IntroductionThe standardization of third-generationmobile communication systems is rapidlyprogressing in all regions of the world. Thework is based on the International TelecommunicationUnion's (ITU) recommendationsfor International Mobile Telecommunications-2000(IMT-2000). By offeringhigh data rates and multimedia capabilities,IMT-2000 systems will enhance the servicesprovided by second-generation systems.'GSM and TDMA (TIA/EIA-136) are twohighly successful second-generation cellularstandards:• more than 256 million people in morethan 120 countries subscribe to GSM; and• the family of TDMA systems (includingEIA-553 and IS-54) serves more than 115million subscribers in over 100 countries.The enhanced data rates for global evolution(EDGE) concept, which is a new timedivisionmultiplexing-basedradio-accesstechnology, gives GSM and TDMA an evolutionarypath for delivering thirdgenerationservices in the 400, 800, 900,1800 and 1900 MHz frequency bands. Theadvantages of EDGE include rapid availability,the reuse of existing GSM andTDMA infrastructure, and support for gradualintroduction. The excellent performanceof EDGE has been demonstrated in a numberof papers."BackgroundEDGE was first proposed to the EuropeanTelecommunications StandardsInstitute(ETSI) in 1997 as an evolution of GSM. Asubsequent feasibility study (completed andapproved by ETSI) paved the way for standardization.7 Although EDGE reuses theGSM carrier bandwidth and timeslot struc-BOX A, ABBREVIATIONS136HS8PSKACANSIARQBCCHBLERBSBSSBSSAP+BSSGPCDFCFCCH136 HighspeedEight-symbol phase-shift keyingAuthentication centerAmerican National StandardsInstituteAutomatic repeat requestBroadcast control channelBlock error rateBase stationBase station systemEnhanced BSS application partBSS GPRS protocolCumulative distribution functionCOMPACT frequency correctionchannelCarrier-to-interference ratioC/lCPAGCH COMPACT packet access grantchannelCPBCCH COMPACT packet broadcastcontrol channelCPCCCH COMPACT packet common controlCPPCHCPRACHCSCHDCCHECSDchannelCOMPACT packet paging channelCOMPACT packet random accesschannelCOMPACT synchronizationchannelDigital control channelEnhanced circuit-switched dataEDGEEGPRSEIAETSIFCCHGGSNGMSCGMSKGPRSGPSGSMEnhanced data rates for globalevolutionEnhanced GPRSElectronic Industries AssociationEuropean TelecommunicationsStandards InstituteFrequency correction channelGateway GPRS support nodeGateway MSCGaussian minimum-shift keyingGeneral packet radio serviceGlobal positioning systemGlobal system for mobilecommunicationHome location registerHLRIMT-2000 International mobileIRISITUIWMSCLALLCLQCMACMCMCSMSCtelecommunications-2000Incremental redundancyInterim standardInternational TelecommunicationUnionInterworking MSCLink adaptationLogical link controlLink quality controlMedia access controlMessage centerModulation and coding schemeMobile services switching centerMTMTPOTAFPACCHPBCCHPCCCHPDNPDTCHPTCCHQoSRLCRTTSCSCCPSGSNSMESMSTDMATETIATNTOMTSTU3UWCCVLRMobile terminalMessage transfer partOver-the-air activation functionPacket-associated control channelPacket broadcast control channelPacket common control channelPacket-data networkPacket-data traffic channelPacket timing advance controlchannelQuality of serviceRadio link controlRadio transmission technologyService centerSignaling connection control partServing GPRS support nodeSignaling message encryptionShort message serviceTime-division multiple accessTerminal equipmentTelecommunications IndustriesAssociationTimeslot numberTunneling of messagesTimeslotTypical urban 3 km/hUniversal Wireless CommunicationConsortiumVisitor location register68 Ericsson Review No. 2, 2000
ture, it is by no means restricted to use withinGSM cellular systems. Instead it can beseen as a generic air interface for efficientlyproviding high bit rates. It thus facilitatesan evolution of existing cellular systems towardthird-generation capabilities.While developing third-generation wirelesstechnology, the TDMA communitychose to adopt an evolutionary approach,basing its proposal for third-generationtechnology on the evolution of currentsecond-generation systems. The UniversalWireless Communication Consortium(UWCC) proposed the 136 High-Speed(136HS) radio interface as a means of satisfyingrequirements for IMT-2000 radiotransmission technology (RTT). Additionalrequirements called for commercially effectiveevolution and deployment in TDMAnetworks:• flexible spectrum allocation;• high spectral efficiency;• compatibility with TDMA;• coverage equivalent to TDMA;• support for macrocellular performance athigh mobile velocities—in particular, theinitial macrocellular deployment shouldnot require more than 1 MHz of spectrum;and• ability to coexist in the same spectrumwith second-generation systems withoutdegrading their performance.After evaluating various proposals, theUWCC adopted EDGE, in January 1998,as the outdoor component of 136HS (laterreferred to as EGPRS-136) to provide 384kbit/s data services. One argument in favorof this approach is that the same technologyevolution can be leveraged for GSM andTDMA systems—which also facilitatesglobal roaming. EDGE was thus includedin the UWC-136 IMT-2000 proposal. InFebruary 1998, this proposal was adoptedby TR-45 and submitted by the US delegationto ITU as an RTT candidate for IMT-2000. 8 In November 1999, the proposal wasapproved as a radio-interface specificationfor IMT-2000. EDGE is currently being developedin two modes for TDMA systems:COMPACT and Classic.COMPACT employs a new 200 kHzcontrol-channel structure. Synchronizedbase stations are used to maintain a minimalspectrum deployment of 1 MHz in a 1 /3frequency-reuse pattern.Classic employs the traditional GSM 200kHz control-channel structure with a 4/12frequency-reuse pattern on the first frequency.EDGE is being developed concurrently inETSI and the UWCC to guarantee a highdegree of synergy in GSM and TDMA systems.The standardization roadmap forEDGE comprises two phases:• Phase I emphasizes enhanced GPRS(EGPRS) and enhanced circuit-switcheddata (ECSD), which technologies were includedin ETSI's 1999 release of the standard.Commercial products will follow in2001.• Phase II, which is being targeted for releasein 2000, is currently being definedto include improvements for multimediaand real-time support.EDGE and EGPRSThe GPRS packet-data system uses the samephysical carrier structure as present-dayGSM cellular communication systems andis designed to coexist with and provide thesame coverage as GSM. The radio interfaceis based on the TDMA-structured GSM systemwith 200 kHz carriers divided intoeight timeslots (TS) using Gaussian minimum-shift-keying(GMSK) modulation. InGPRS, each timeslot can typically serve severalpacket-data users, and users can be allocatedmore than one timeslot to increasedata throughput.The GPRS specification includes fourcoding schemes—which scheme is used dependson the quality of the radio carrier.With GPRS, it will be possible to obtaindata rates well over 100 kbit/s.'EDGE introduces higher level modulationand new coding schemes for packetswitchedand circuit-switched data communication.In addition to GMSK modulation,EDGE introduces eight-symbol phaseshift-keying(8PSK) modulation. The symbolrates for GMSK and 8PSK are the same;that is, approximately 271 kilosymbols persecond. The introduction of EGPRS increasesmaximum bit rates to approximatelythree times that of standard GPRS.New techniques introduced with EDGEoptimize the data throughput for each radiolink. One such technique, called link qualitycontrol (LQC), combines link adaptation(LA) and incremental redundancy. The LAfunctionality adapts coding and modulationrelative to signal quality. In poor radio conditions,robust coding and GMSK modulationare selected, whereas in good radio conditions,less robust coding and 8PSK modulationare employed. EGPRS also featuresbackward error-correction functionality,Ericsson Review No. 2, 2000
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TABLE 2. IMPORTANT PARAMETERS FOR N
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