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1CDMA原理2主要内容•码分多址的基本原理•码分多址的关键技术•CDMA同GSM的比较3目标•不同用户是如何用码区分出来的•三种CDMA码的用途•CDMA逻辑信道的划分•编码，软切换和功率控制4•码分多址的基本原理•码分多址的关键技术•CDMA同GSM的比较5•NUsers/WidebandChannel•C/IisstillnegativeafterI.F.filteringbutpositiveafterdespreadingprocess•Canconsiderdespreadingasthelastfilteringstage•3Users/NarrowbandChannel•C/IisnegativepriortoI.F.filteringandpositiveafterfiltering1231TDMA(3timeslotsshown)30kHzFrequencyTime•1User/NarrowbandChannel•C/IisnegativepriortoI.F.filteringandpositiveafterfilteringFDMA30kHzFrequencyTimeDS-CDMA1.23MHzFrequencyTimeCDMACDMA基本原理WalshCode6IS-95wasaninterimstandarddevelopedbyTIA/EIA.IS-95definedmobilestationandbasestationcompatibilityforthefirstapplicationofCDMAtechnologyincellularsystems.TIA/EIAisanaccreditedstandardsdevelopmentorganizationthroughtheANSITIA/EIA:TelecommunicationsIndustriesAssociation/ElectronicsIndustriesAssociationANSI:AmericanNationalStandardsInstituteIS-95接口标准7MSCCBSCPSTNBTSCDMA系统网络结构8BTSCBSCCDMAIS-95A+系统结构实例开放的网结构OpeningNetworkArchitectureCDGIOSCellSiteVoiceControlLInterfaceUNOOMC-RBTSBTSXCIWUMMMSC/VLRCDGIOSPSTNPSTNINApplicationHLRMSCSMSVMSANSI-419CDMA物理信道Tx:870--880MHzRx:825--835MHz10CDMA首选载波分配SystemDesignatorPreferredSetChannelNumbersA283(Primary)691(Secondary)B384(Primary)777(Secondary)11联通拥有的频率资源825835845CDMATx870880CDMARx960CDMA/AMPSUCCDMASpectrumAllocationGSMRx915GSMTxFreq(MHz)CMCCGSM935890909UCGSMUCUC954ABandBBandABandBBandCMCC894CMCC93912CDMA的基本原理：CDMA码•PN码（伪随机噪声序列）貌似随机，实际上是有规律的周期性二进制序列。在CDMA中用到两个伪随机序列，长码和短码。•WalshCode具有正交特性13伪随机码(PNCODE)的生成01000111004010210151106111701130011142567314010001110041106111701131015010200111467352伪随机码(PNCODE)15Walsh码递归公式168阶Walsh码W000000000W101010101W200110011W301100110W400001111W501011010W600111100W70110100117CDMACodes•PNshortcodeLength＝215－1＋1＝215＝32，768chips•Walshcode64•PNlongcodeLength＝242-14.4×1012chips18CDMA系统中采用的编码Walsh码•在CDMA前向逻辑信道中使用,以区分同一小区或扇区用户19PN短码•区分不同扇区或小区•伪随机序列•215=32,768unit(period26.67ms)•用于前向及反向物理信道扩频CDMA系统中采用的编码2064chips32,768chips/64=512PNoffsets......PNchipsPN短码偏置21长码•用于反向逻辑信道区分不同用户•伪随机序列•242-1unit•在前向链路上对业务及寻呼信道进行扰码CDMA系统中采用的编码22CDMA前向信道结构PilotChanPagingCh1PagingCh7SyncChanCodeCh1•••W1W32W7W8W0UptoFORWARDCDMACHANNEL(1.23MHzchanneltransmittedbybasestation)CodeChPCodeChSCodeCh55W63•••UptoCodeChN••••••W=CodeChannelMobileStationPowerControlSub-ChannelFundamentalCodeChannelDataUptoMobileStationPowerControlSub-ChannelFundamentalCodeChannelDataSupplementalCodeChannelDataUpto•••ForwardTrafficChannelconsistingofonecodechannelForwardTrafficChannelconsistingofmultiplecodechannels23CDMA反向信道结构REVERSECDMACHANNEL(1.23MHzchannelreceivedbybasestation)AccessChannelassociatedwithPagingCh1AccessChannelassociatedwithPagingChPTrafficChanTTrafficChan1FundamentalCodeChannelSupplementalCodeChannel1SupplementalCodeChannelSAddressedbyLongCodePNsAccessChannelassociatedwithPagingChPAccessChannelassociatedwithPagingCh1.....................24CDMA前向信道结构25CDMA前向信道结构26CDMA反向信道结构27CDMA反向信道结构28OverheadChannelsTrafficChannelsCarrymessaging,IdentificationandPrimarilycarryvoiceanduserdatatiminginformationtrafficCarrysomesignalinginformationusedtocontrolMSPilotSyncForwardForwardTrafficPagingAccessReverseReverseTrafficCDMA基本原理29PilotSyncPagingTrafficDSSbyWalsh0DSSbyWalsh32DSSbyWalsh1-7DSSbyremaining55Walshcodes64logicalchannelsarecombinedThenquadraturespreadusingpilotPNcodeCDMA基本原理30Spreadbylongcode(offset)Spreadbylongcode(offset)AccessTrafficQuadraturespreadusingpilotPNcodewithoutanyoffsetCDMA基本原理31•码分多址的基本原理•码分多址的关键技术•CDMA同GSM的比较32•码激励线性预测编码(CELP)•功率控制•软切换CDMA关键技术33CELP•CodeExcitedLinearPredictive•CompresseddigitalvoicebetweenXCandMS•Usesmuchlessdatatoapproximatetheoriginalsignal•8Kor13K34功率控制•反向开环功率控制•反向闭环功率控制•前向闭环功率控制35功率控制的重要性36ForwardReverse远近效应功率控制Basedon:powermeasurement(Eb/No)frameerrorrate(FER)37TimeAccessProbesInitialPowerInitialPower+openloopcorrectionTxPower(dbm)开环功率控制38开环功率控制：•AssumesLossisSimilaronForwardandReversePaths•ReceivePower+TransmitPower=-73–AllpowersindBm•Example:–ForaReceivedPowerof-85dBm•TransmitPower=(-73)-(-85)•TransmitPower=+12dBm•ProvidesanEstimateofReverseTXPowerforGivenPropagationConditions39反向功率控制：•MaximumSystemCapacityisAchievedif:•AllMobilesarePoweredControlledtotheMinimumPowerforAcceptableSignalQuality•Asaresult,allMobilesareReceivedatAboutEqualPowerattheBaseStationIndependentofTheirLocation•ThereareTwoTypesofReverseControl:–OpenLoopPowerControl–ClosedLoopPowerControl•Open&ClosedLoopPowerControlareAlwaysBothActive40闭环功率控制：•DirectedbyBaseStation•UpdatedEvery1.25msec•CommandsMobiletoChangeTXPowerin+/-1dBStepSize•FineTunesOpenLoopPowerEstimate•PowerControlBitsarePuncturedovertheEncodedVoiceData•PuncturePeriodistwo19.2kbpsSymbolPeriods=103.6usec41FDMA&TDMA切换Break-before-make42CDMA软切换Make-before-break43CDMA软切换•更软切换•软切换•CBSC间软切换44NarrowBandCellsCompeteHardHand-OffMobilePositionCellACellBSoftHandoffSignalStrengthABCDMACellsTeamupSoftHand-OffBreakBeforeMakeMakeBeforeBreak软切换45软切换导频集ActiveActiveActiveNeighborNeighborNeighborNeighborNeighborNeighborNeighborRemainingRemaining•有效导频集•相邻导频集•剩余导频集•候选导频集46软切换Threshold&TimerT-AddT-CompT-Drop