channelcoding信道编码英文知识

1,ErrorControlCoding,ErrorControlStrategies,PerformanceMeasures,Outline,ErrorControlStrategiesForwardErrorCorrection(FEC)AutomaticRepeatRequest(ARQ)HybridARQPerformanceMeasuresProbabilityofdecodingerror(errorprobability)CodinggainShannonLimit,2,ForwardErrorCorrection(FEC)One-waysystem,evennotstrictlyone-wayDigitalstoragesystems,deep-spacecommunicationsystemsandmostofthecodedsystemsinusetodayAutomaticRepeatRequest(ARQ)Two-waysystemsomedatanetworksandsatellitecommunicationsystems,ErrorControlStrategies,3,FEC,Employerror-correctingcodesAutomaticallycorrecterrorsdetectedatreceiverThisbookisdevotedmostlytotheanalysisanddesignofFECsystem,4,ARQ,Stop-and-waitARQContinuousARQGobackNSelectivereject(selectiveretransmission),5,Stop-and-waitARQVSContinuousARQ,ContinuousARQismoreefficientContinuousARQismoreexpensiveStop-and-waitARQdesignedforhalf-duplexchannelsContinuousARQdesignedforfull-duplexchannels,6,ARQVSFEC,ARQrequiresmuchsimplerdecodingequipment(Actuallyonlydetectingnocorrecting)ARQisadaptiveinthesensethatinformationisretransmittedonlywhenerrorsoccurWhenerrorrateishigh,thesystemthroughputisloweredbyusingARQAhybridcombinationofFECismoreefficientthanARQalone,7,Howtomeasuretheperformanceofacodedsystem?(AcurveofBERvs)Probabilityofdecodingerror(errorprobability)-YdirectionCodinggain-Xdirection,PerformanceMeasures,8,Errorprobability(WERandBER)Probabilityofword(orblock)error-WER-WorderrorrateProbabilityofbiterror-BER-BiterrorrateThesetwoerrorprobabilitiesshouldbekeptaslowaspossible,ErrorProbability,9,ErrorProbability(RelationbetweenEbandEs),Theenergy-per-informationbit:energypertransmittedsymbolR:coderate,R=k/ncommonlyusedtoexpresserrorprobability:one-sidedPSD(PowerSpectrumDensity)ofthechannelnoise,10,ErrorProbability-Ydirection,11,3.7dB,Codinggain,ThereductionintheEb/Norequiredtoachieveaspecificerrorprobability(BERorWER)CodinggainisimportantincommunicationapplicationsCodingthresholdistheSNRatwhichthecodinggainactuallybecomesnegativeAsymptoticcodinggainthecodinggainforlargeSNR,12,Codinggain,13,Codingthreshold,Codinggain,14,ShannonLimit,Definition:theminimumSNRrequired-error-free-codedsystem-coderateRMeaning:SNRshouldexceedsShannonlimitUse:measurethemaximumachievablecodinggain,15,-error-free-AWGN-BPSK-codedsystem-R=0.5-Shannonlimit:0.188dB,FigureofShannonlimit,0.188dB,R=0.5,16,R:00.99Eb/No:ShannonlimitExample:-AWGNchannel-BPSK-10-5-uncodedsystem:9.65dB-codedR=0.5:0.188dB-(codinggain)max:9.462dB(Soyoucancomparedifferentcodingschemestoseewhichoneisbetter),TableofShannonlimit(Ref.ShuLin),BERPerformanceofConvolutionalCode,17,Codinggain:4.15dB,(Codinggain)max:9.462dB,Improvementgap:3.962dB,Shannonlimit:0.188dB,4.15dB,