Carrier Synchronization of Offset Quadrature.pdf

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1、TMOProgressReport42-133May15,1998CarrierSynchronizationofOffsetQuadraturePhase-ShiftKeyingM.K.Simon1Thisarticlecontainsanalysesoftheperformanceofvariouscarriersynchro-nizationloopsforo®setquadraturephase-shift-keying(OQPSK)modulation,allmotivatedinoneformoranotherbythemaximumaposterior

2、i(MAP)estimationofcarrierphase.Whentheyareimplementedaseitherhighorlowsignal-to-noiseratio(SNR)approximationstothegenericimplementationsuggestedbytheMAPestimationofcarrierphaseforanOQPSKsignal,itisshownthattheloopsbehavemorelikebiphasethanquadriphaseloopsinthattheyonlyexhibita180-degph

3、aseambiguityratherthanthe90-degphaseambiguitytypicalofthelatter.Thisphaseambiguityadvantagecoupledwiththemean-squaretracking-errorperformancead-vantagethatresultsanditsultimatee®ectonaverageerrorprobabilityperformanceo®erapotentiallysigni¯cantjusti¯cationforusingOQPSKratherthanQPSKeven

4、onalineartransmissionchannel,whereitoftenisreasoned(basedontheassump-tionofanidealenvironment)thatthetwomodulationschemesperformidentically.I.IntroductionTheproblemofsuppressed-carriersynchronizationindigitalcoherentcommunicationsystemshasreceivedwidespreadattentionovertheyearsfromathe

5、oreticalaswellasapracticalpointofview.Inreality,thesetwopointsofviewarenotseparatefromeachotherinthatthecarriersynchronizationstructuresthatcommonlyareemployedinthedesignofcoherentreceiversarethosethataremotivatedbytheapplicationofthemaximumaposteriori(MAP)estimationtheory[1].Acommonex

6、ampleofthisistheCostasorin-phase{quadrature(I-Q)loop[2,3]forbinaryphase-shift-keying(BPSK)systemsthatisderivedbysuitablyusingthederivativeoftheopen-loopMAPestimateofcarrierphaseastheerrorsignalinaclosed-loopcon¯guration.ClosedloopsderivedinsuchafashionoftenarereferredtoasMAPestimationl

7、oops[1,4],andthisterminologylikewiseshallbeusedhereinthisarticle.Extensionoftheaboverelationshipbetweenopen-loop(MAP)carrierestimationandclosed-loopsynchronizationschemestoM-arymodulationschemessuchasmultiplephase-shiftkeying(MPSK)andquadratureamplitude-shiftkeying(QASK)alsohasbeenco