TD-SCDMA系统工作原理及发展

TD-SCDMAFeaturesandDevelopmentDr.ShiheLie-mail:[e-mail]s•Background•FeaturesofTD-SCDMA•Development•ConclusionOneGenerationper10years7080900010R/D1G(FDMA)2G(TDMA)4G？StandardWidelyapplicationProductDevelopment3G(CDMA)Mainrequirement•Billionsmobilephoneusers–Capacityissue•Dataapplication–Asymmetricservices•Servicecost–Equipmentcost3GhastosolvetheaboveproblemSpectrumEfficiencyforvoiceservicesin1/2Gsystems•1GFDMA(TACS)–2x25kHzfor1voicech.,frequencyre-usefactor=11–Spectrumefficiency=1/0.05/11=1.8ch/cell/MHz•2GTDMA(GSM)–2x200kHzfor8voicech.,frequencyre-usefactor=7–Spectrumefficiency=8/0.4/7=2.8ch/cell/MHz•2GCDMA(IS-95)–2x1.25MHzfor20voicech.,frequencyre-usefactor=1–Spectrumefficiency=20/2.5/1=8ch/cell/MHz•Theoretically,ifallcodecanbeused,thespectrumefficiencymayreach64/2.5/1=25.8ch/cell/MHz,whichisnearly14timesofFDMAand8timesofTDMA.BasicCDMAconcept•SpectrumSpreadingisatechnologyusedinmilitarycommunicationsince60’s•Basicconcept–Spreadingcode:Walshcode,itisanorthogonalcodewhensynchronized–CDMAisaself-interferencesystem:•Multiplexinterference:betweencodechannels•Multi-pathandDoppler•Interferencefromothersystemandusersinadjacentcell–Near-fareffect–CapacityofaCDMAsystemislimitedbytotalinterferencelevelCapacityinCDMAsystem:Generalsituation•Basicconsumption:–Idealpowercontrol,receivedpowerlevelfromeachactiveUEisthesame:Eb–Userdistribution:uniform•WhenNusersareactive,thentheinterferencefromthesamecellwillbe(N-1)Eb.Thetotalinterferencefromtheadjacentcells(1stand2ndlayers)willbethesameasthatfromthesamecell.•TotalreceivedEb/N0≤lg(SF)+Eb/(N0+2*(N-1)Eb)~lg(SF)-lg(2N)N≤(10lg(SF)-Eb/N0)/2~(0.25-0.3)SF•ReduceinterferenceTechnologiesrelatedtocapacity•Macrodiversity–UEgetdown-linkfrom2to3BSs–EachBSmaytransmitlesspower,lessinterferencetoenhancedown-linkcapacityabout2dB•Powercontrol–Powercontrolerror:usually2to3dB–Becauseoffastfadingandmulti-path–Capacityloss:2dB•VariableratevocoderBasicconceptofDuplexFFdownFup•Duplex:communicationbetweenUEandBSsimultaneously•Traditionaltech:dividedbyfrequency:FDD•TimeDivisionDuplex(TDD)isfromdatacommunication•Fromendof80’s,TDDstartedtouseinvoicecommunication(CT2,DECT,etc.)•From3G,TDDbecomeoneduplexinRTTtDownlinkdataUplinkdataTSdownTSuptComparisonbetweenFDD&TDDItemsFDDTDDTransmissionPpeak/aveContinuous,lowBurst,highReceivingsensitivityhigh(BW=datarate)low(BWdatarate)CommdistanceinsamePmaxLongShortNumberofcarrierf2,downandupseparationbyfrequency1,downandupseparationbytimeWavepropagationindown-andup-linkdifferentSameatthesametimeNeedduplexerintransceiverYesinUETwoantennasinBSNoneinUEOneantennainBSAsymmetricdataSomespectrumresourcemaynotbeusedAllspectrumresourcecanbeusedMainFeatureinTDDDuplex•Spectrumflexibility:donotneedpairedfrequency•SamecarrierfrequencyinbothDown-andUp-link,symmetricpropagationperformancesuitableforsmartantenna,pre-Rake,openlooppowercontrolandothertechnologies•Supportasymmetricdataservices,byadjustingdifferentnumbersofslotsinup-and/ordown-link–ItmayuseofdifferentbandwidthforasymmetricservicesinFDD,butitcouldnotbeflexible•Lowcost:DonotaskhighisolationbetweenTxandRxpath,onemaydesignsingleICforRFtransceiverinUEMainShortageforTDD•Higherpeak/averagetxpowerratioforUE–FDD:continuoustransmit–TDD:onlyoneTSwork,theextraratiowillbe10lgM,MisthenumberofTS–HigherrequirementfortransmitterandPA.•Lowersensitivityforreceiver–Bandwidth:thetotalchiprate–Datarate:limitedbynumberofTS–Sensitivityloss:10lgM.•Discontinueoperation–Lesscommunicationdistance,halfnearly–Difficultforhighspeedmoving.tHowtoovercometheshortages?•TheshortageofTDDleadsto:–TDDcanonlybeusedinMicro-andPico-cell–TDDcanonlysupportslowmoving•Possiblewaytoovercometheshortages–Smartantenna:increasesensitivityandEPRI–SmartantennaplusJointdetection:improveperformanceinfastfading(multi-pathinhighspeedmoving)Contents•Background•FeaturesofTD-SCDMA•Development•ConclusionCapacityinCDMAsystem:Generalsituation•Basicconsumption:–Idealpowercontrol,receivedpowerlevelfromeachactiveUEisthesame:Eb–Userdistribution:uniform•WhenNusersareactive,thentheinterferencefromthesamecellwillbe(N-1)Eb.Thetotalinterferencefromtheadjacentcells(1stand2ndlayers)willbethesameasthatfromthesamecell.•IftheantennaofBSwithbeamformedpattern,thenonlyapartofinterferencewillbeinterdemodulator.•Eb/N0≤lg(SF)+Eb/(N0+(2*(N-1)Eb)/m)~lg(SF)-lg(2N/m)N≤m(10lg(SF)-Eb/N0)/2mmeanscoverageanger/beamwidthFeaturesofSmartAntenna•Increasereceivingsensitivity•IncreaseEIRP•ReduceInterference•IncreaseCapacityofsystem•ReducecostofBS•IncreasereliabilityofBSFeaturesofsynchronousCDMA•Inmulti-pathcondition,idealsynchronizationcannotbereached•Onecandoissynchforthemainray,andtakestheotherrayasinterferenceornoise•Themainfeatureistosyncallup-linksignalsinthesametimeslot,simplifydataprocessionBasicconceptofSR•Multi-bandandmulti-standardinmobilecommunication•Eachstandardaskdifferentequipmentdesign•Composeofaradioequipment:–Antennaandcable:wideband–RFtransceiver:differentbandwidth–BBdigitalsignalprocessor–CtrlandI/O:switchandMCU•Themostactivetechnology:inBBDSP•Softwareradio(SR):b