南邮数字通信课件chapter 11new

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1、Chapter11MultichannelandmulticarrierSystem•Multichannelsystemshereactuallyarediversitysystems•Multicarriersystemsubdividesthefrequencybandofthechannelintoanumberofsubchannelsandinformationistransmittedoneachofthesubchannels.Thistechniquenowwidelyusedindigitaltransmissionovercopperwiresubs

2、criberloopsandinradiochannels(WLAN,WMAN,B3G/4G),eveninfutureaudiobroadcastapplication.11.1MultichannelDigitalCommunicationinAWGNChannelsm:m-thwaveform;L:thenumberofchannels;Channel1~:frequencynon-selective:()nn()j2ftcs()tRe[s()te],0tTn;1,2,Lm;1,2,MmlmForfrequencynonselectivechannels

3、n-thchannel()nn-jφn()r()tαes()tzt()lnlmn()ngs()tzt(),0tTn;1,2,Lm;1,2,MnlmnForcoherentreceiver,usingmatchedfilterLT()n*(n)*CMmlRer()tgsˆnlm(t)dt,m1,2,,Mn10Fornon-coherentreceiver,e.g,usingsquare-lawdetection2LT()n(n)*CMmlr()tslm(t)dt,m1,2,,Mn1011.1-1BinarySignals()n

4、Ifsistransmitted,theprobabilityoferrorisl1theprobabilityofD=CM1-CM2<0,AppendixBshowsthatforBPSK,ifthechannelsareperfectlyestimatedandwithcoherentdemod,thenPQ(2)(11.1-10)bbwhere,LL22bng=n(11.1-11)NN00nn11istheenergyineachchannel.22If,nL2(11.1-12)bN0Theconclusionisthat,us

5、ingLchannelstotransmitasameinformationwithenergyeach,theresultisthesameasusingonechannelwithenergyL.Theproblemis,withfadingchannelonechanneltransmisionwithenergyLwilldegradatetheperformancegreately.Somulti-channel(diversity)willbeused.Ifthechannelestimationisnotperfecttheresultisshowni

6、nappendixCandtherewillbealossinperformance.•ForbinaryDPSKandsquarelawdetectionoforthogonalsignalstransmittedoverLchannels,thereislossresultingfromnon-coherentcombination(B-21).ThecombininglossisshowninFigure11.1-2.11.1-2M-aryOrthogonalSignals(squarelawdetectionandcombiningonLchannels)(11.

7、1-22)isexactperformanceexpression,and(11.1-23)and(11.1-24)areupperbounds.Figure11.1-2combining11.2MulticarrierCommunications11.2-1Signal-CarriervsmulticarrierModulation*Multicarriersystemsubdividesthefrequencybandofthechannelintoanumberofsubchannelsandinformationist