现代数字通信.pdf

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1、ModernDigitalCommunicationsModernDigitalCommunications现代数字通信现代数字通信Chapter13FadingChannelsI:CharacterizationandSignalingZhi-NianLuo,AssociateProfessorVer.2015Chapter13Zhi-NianLuo现代数字通信现代数字通信第第1212讲讲衰落信道：表征与信号传输衰落信道：表征与信号传输FadingChannelsI:CharacterizationandSignalingVer.2015Chapter13Zhi-N

2、ianLuo13.1CharacterizationofFadingMultipathChannels衰落多径信道表征ThemultipathfadingchannelswithadditivenoiseCADBTransmitterReceiverVer.2015Chapter13Zhi-NianLuo13.1CharacterizationofFadingMultipathChannelsTimespreadphenomenonofmultipathchannels(Unpredictable)Time-variantfactors多径信道时间扩展时变因素òDel

3、ayòNumberofspreadsòSizeofthereceivepulsesVer.2015Chapter13Zhi-NianLuo13.1CharacterizationofFadingMultipathChannelsTransmittedsignalReceivedsignalinabsenceofadditivenoisetheequivalentlowpasschannelisdescribedbythetime-variantimpulseresponse时变冲激响应Ver.2015Chapter13Zhi-NianLuo13.1Characteri

4、zationofFadingMultipathChannelsFortroposphericscatterchannel对流层散射信道whereα(τ;t)denotestheattenuationofthesignalcomponentsatdelayτandattimeinstantt.连续多径分量Theequivalentlowpasstime-variantimpulseresponseVer.2015Chapter13Zhi-NianLuo13.1CharacterizationofFadingMultipathChannelsLow-passimpulse

5、response离散多径信道连续多径信道Notethatnowitisnotappropriatetowrites(t)*c(t)llbecausetandτarenowspecicallyfortimeargumenandconvolutionargument,respectively!Weshouldperhapswrites(t)*c(τ)ands(t)*c(τ;t)llllVer.2015Chapter13Zhi-NianLuoRayleighandRicianThemeasurementsuggeststhatc(τ;t)isa2-DGaussainrand

6、omprocessint(notinτ),whichcanbesupportedbythecentrallimittheorem(CLT)becauseitisthe‘sum’effectofmanypaths.òIfzeromean,

7、c(τ;t)

8、isRayleighdistributed.ThechannelissaidtobeaRayleighfadingchannel.òIfnonzeromean,

9、c(τ;t)

10、isRiciandistributed.ThechannelissaidtobeaRicianfadingchannel.Whendiversit

11、ytechniqueisused,c(τ;t)canbewellmodeledbyNakagamim-distribution.DetailofthesedistributionscanbefoundinSection2.3.Ver.2015Chapter13Zhi-NianLuo13.1-1ChannelCorrelationFunctionsandPowerSpectra信道相关函数与功率谱Cassumec(τ;t)iswidesense-stationary.ADThendefinetheautocorrelationfunctionBTran