北大数字通信课件：a-- 20 GSM移动通信系统

1数字通信(第二十讲)GSM无线通信系统2008-12YupingZhao(Professor)赵玉萍DepartmentofElectronicsPekingUniversityBeijing100871,Chinaemail:[e-mail]2EventsinthedevelopmentofGSMYearEvents1982CEPTestablishesaGSMgroupinordertodevelopthestandardsforapan-Europeancellularmobilesystem(工作组成立)1985Adoptionofalistofrecommendationstobegeneratedbythegroup(若干标准建议被接收)1986Fieldtestswereperformedinordertotestthedifferentradiotechniquesproposedfortheairinterface(进行了场强测试)1987TDMAischosenasaccessmethod(infact,itwillbeusedwithFDMA)(确定了基于TDMA/FDMA的接入方式)1988ValidationoftheGSMsystem(验证了GSM系统)3EventsinthedevelopmentofGSM1989TheresponsibilityoftheGSMspecificationsispassedtotheETSI(ETSI承担了GSM标准化工作)1990Appearanceofthephase1oftheGSMspecifications(GSM标准1出现)1991CommerciallaunchoftheGSMservice(GSM开始商用)1992EnlargementofthecountriesthatsignedtheGSM-MoUCoverageoflargercities/airports(扩大GSM覆盖到大城市及机场等地区)1993CoverageofmainroadsGSMservicesstartoutsideEurope(覆盖到欧洲之外国家)1995Phase2oftheGSMspecificationsCoverageofruralareas(GSM标准2出现)4GSM网络构成5GSMmobilenetworkArchitectureoftheGSMnetwork6主要特性--MainFeaturesofGSM频段Frequency:890~915,935~960MHz(GSM900)or1710~1785,1805~1880MHz(DCS180)频带间隔Frequencyinterval:200kHzFrequencyhopping:onewaytoapplycdmabetweencellsusingthesamefrequency调制方式Modulation:GMSK270.833Kbit/s7Frequencybands•Frequencyband:Uplink:890-915MHz,Downlink:935-960MHz•Frequencyrange:50MHz(25MHzUp,25MHzDown)•Carrierspacing:200KHz(buttimesharedbet.8subscribers)•Duplexdistance:45MHz(FDD)8Frequencybands•Numberofcarriers:25MHz/200KHz=125,allowingforguardband,only124carriers•Users/carrier:8•Inorderthataterminaldoesnottransmitandreceivesimultaneously,thereversechannelisretardedby3timeslotsrelativetotheforward9GSMmobilenetworkFramestructureofGSM10GSMFrames•Controlframes–containcontrolchannelidentifier–usesSlot0ofcertaincarriers•Trafficframes–supportsupto8fullrate/16halfratetrafficchannels–approximately25%channelcodingoverheadTDMAFrame:Slot0Slot1Slot3Slot4Slot5Slot6Slot7Slot2-Eachframeis4.615msec-Eachframehas1250bits-270.833Kbps-Eachcarriersupports270.833Kbps-Eachuserhasmaximumrateof270.833/8=33.854kbps357(data)138.25SlotFormat:57(data)126156.25bitsTailbitsFlagTrainingFlagTailbitsGuardPeriod11Trafficframes&controlframes•Thetrafficandcontrolframesarenotamultipleofeachother•Anyframenumberwilloccursimultaneouslyinbothmultiframesevery1326(26X51)or6.12seconds12Frequencybands•OneormorecarrierfrequenciesareassignedtoeachBS•Timeslotisapprox.0.577msor156.25bits(1bitin3.69ms)•1physicalchannelis1timeslotperTDMAframe•EighttimeslotsaregroupedintoaTDMAframeor4.615ms13Conventionalcarriers•Theconventionalcarrierisasinewaveatasinglefrequency14Slowfrequencyhoppedcarriers•EachTDMAframeinagivenchanneliscarriedoncarrierfrequenciesthatchangesovereachframe•FrequencyhoppingaddsanewdimensionofcomplexitytocellularreuseplanningPurposesoffrequencyhopping:•reducesvulnerabilityofsignalstofrequencyspecificimpairments•reducesco-channelinterferencebetweensignalsinnearbycellsEffectofhopping•Interferenceoccursonlyforafractionofthetime,errorcorrectioncodemitigateseffectofimpairment15•AssumeN=3(dependsonenvironment)•Countryside:N=2or3;•Metropolitanareas:N3orhigherCarriers:124;eachcarrierhas8channels:No.ofphysicalchannels=124*8=992Totalfrequencyband:25(uplink)+25(downlink)=50MHzEfficiency=992/(3*50MHz)=6.61conversations/cell/MHzSpectrumefficiency16MainFeaturesofGSM(continued)语音编码方式from13Kbits/s(每个频段8通道)6Kbits/s(每个频段16通道)提高频带利用率的方法:尽可能少的信令功率控制等17DelayRequirements•SpeechCodingAlgorithmicDelay20ms•InterleavingDelay37ms•ProcessingDelay8ms•OtherDelayinradiosubsystem15ms•OverallDelay80ms18GSMmobilenetworkRadioresourcesmanagementfrequencyhoppingpowercontrolDiscontinuoustransmission(DTX)1920GSMmobilenetworkMobileStationThemobilestation(MS)consistsofMobileequipment(theterminal)SubscriberIdentityModule(SIM).ThemobileequipmentisuniquelyidentifiedbytheInternationalMobileEquipmentIdentity(IMEI).TheSIMcardcontainsofInternationalMobileSubscriberIdentity(IMSI)usedtoIdentifythesubscribertothesystemAsecretkeyforauthentication2122GSMmobilenetworkBaseStationSubsystem•composedoftwoparts:BaseTransceiverStation(BTS)BaseStationController(BSC)BaseTransceiverStation:HandletheradiotranceiversthatdefineacellHandlestheradio-linkprotocolswiththeMobileStationTheBaseStationControllermanagestheradioresourcesforoneormoreBTSs.Radio-channelsetupFrequencyhoppingHandovers2324GSMmobilenetworkNetworkSubsystem(NSS)centralcomponent:MobileservicesSwitchingCenter(MSC)MSCactsasanormalswitchingnodeofthePSTNorISDNProvidesallthefunctionalityneededtohandlemobilityRegistrationAuthenticationLocationupdatingHandovers25MSCconnectiontothefixednetworks(SignallingSystemNumber7-SS7)callroamingHomeLocationRegister(HLR)VisitorLocationRegister(VLR)26HomeLocationRegister(HLR)containsalltheadministrativeinformationofeachsubscriberregisteredinGSMnetworkthecurrentlocationofthemobile27GSMmobilenetworkVisitorLocationRegister(VLR):containsselectedadministrativeinformationfromtheHLR,necessaryforcallcontrolandprovisionofthesubscr