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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()tgs?nlm(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
