无线通信原理课件 第五章.ppt

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1、MultipleAccessTechniquesforWirelessCommunicationsChapter 52021/9/91ContentsofChapter 51.IntroductiontoMultipleAccess2.FDMA,TDMAandCDMA3.PacketRadio4.CapacityofCellularSystems2021/9/92Chapter 51.IntroductiontoMultipleAccess2.FDMA,TDMAandCDMA3.PacketRadio4.CapacityofCellula

2、rSystems2021/9/93Wirelessspectrumresourceislimited!AMPS:900MHzGSM:2021/9/94Multi-UserCoinstantaneousCommunication“MA”“Capacity”2021/9/95Whatismultipleaccess?2021/9/96Frequency(f)Time(t)Code(c)Space(s)PacketRadioGoal:multipleuseofasharedmediumMultipleAccessMultipleAccessTe

3、chniquesFDMATDMACDMASDMAPR2021/9/97MultipleaccessAccordingtowhethertherearecollisionsinchannels,themultipleaccesstechniquescanbeclassifiedinto:Non-collisionmultipleaccessCollisionmultipleaccess2021/9/98Multipleaccess2021/9/99Multipleaccess——PacketRadio:分组无线电2021/9/910Dupl

4、exingFrequencydomaintechniques:FDDTimedomaintechniques:TDD2021/9/911FDDsystems2021/9/912TransmitterReceiverBPFTransmitterReceiverBPFF1F1MobileStationBaseStationSynchronousSwitchesTDDsystems2021/9/913FDMATDMACDMA2021/9/914CellularSystemsMATechniqueAMPS(AdvancedMobilePhones

5、ystem)FDMA/FDDGSM(GlobalSystemforMobile)TDMA/FDDIS–95(U.SNarrowbandSpreadSpectrum)CDMA/FDDWCDMACDMA/FDD,CDMA/TDDTD-SCDMACDMA/TDDCdma2000CDMA/FDDMultipleascesstechnologiesusedindifferentwirelesssystems2021/9/915Chapter 51.IntroductiontoMultipleAccess2.FDMA,TDMAandCDMA3.Pac

6、ketRadio4.CapacityofCellularSystems2021/9/916FDMA(PP.450)2021/9/917FDMAEachuserisallocatedauniquefrequencybandorchannel.Thesechannelsareassignedondemandtouserswhorequestservice.ThebandwidthofFDMAchannelsisnarrow(30KHz)sinceitsupportsonlyonecall/carrier.ISIislowsincethesym

7、boltimeislargecomparedtoaveragedelayspreadNoequalizationisrequired.SeparationofthewholespectrumintosmallerfrequencybandsAchannelgetsacertainbandofthespectrumforthewholetime2021/9/918FDMASinceFDMAisacontinuoustransmissionscheme,fewerbitsareneededforoverheadpurposes(suchas

8、synchronizationandframingbits)ascomparedtoTDMA.TheFDMAmobileunitusesduplexers.FDMArequirestightR