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基于Turbo码迭代的低信噪比载波同步技术
1.Introduction
Carriersincommunicationsystemsareoftensusceptibletonoiseandinterferencethatcandegradethequalityofthetransmittedsignal.Carriersynchronization,alsoknownascarrierphasesynchronization,isanimportantpartofcommunicationsystemswhichaimstorecoverthetransmittedcarriersignalatthereceiverregardlessofthenoiseandinterference.Thispaperfocusesondiscussingacarriersynchronizationtechniquebasedonturbo-codediterativealgorithmsinlowsignal-to-noiseratio(SNR)scenarios.
2.TurboCodesandCarrierSynchronization
Turbocodesareaformoferror-correctingcodesusedindigitalcommunicationsystems.Thesecodesusetwoormoreconstituentconvolutionalcodestoprovideenhancederrorcorrectioncapabilities.Turbocodesemployaniterativedecodingprocessinwhichsoftinformationisexchangedbetweentheconstituentdecoderstoimprovetheaccuracyofthedecodingprocess.
Theiterativedecodingprocessofturbocodeshasbeenutilizedincarriersynchronization.InlowSNRscenarios,thereceivedcarriersignalmaybetooweaktobedetecteddirectly.Insuchacase,thecarriersynchronizationalgorithmmakesuseoftheiterativedecodingprocessofturbocodestorecoverthetransmittedcarriersignal.Theturbo-codediterativecarriersynchronizationalgorithmisimplementedatthereceiverend,anditoperatesiterativelywiththedemodulationalgorithmtorecoverthecarriersignal.
3.DescriptionoftheTurbo-codedIterativeCarrierSynchronizationAlgorithm
Theturbo-codediterativecarriersynchronizationalgorithminvolvesthefollowingsteps:
Step1:Thereceivedsignalisconditionedusingabandpassfilterthatmatchesthebandwidthofthetransmittedsignal.
Step2:Theconditionedsignalissampledanddown-convertedtobasebandtoobtainthecomplexsymbols.
Step3:Thesoftdecisionsofthedemodulationalgorithmonthecomplexsymbolsareutilizedtoprovidetheinitialestimateofthecarrierphase.
Step4:Theinitialestimateofthecarrierphaseisusedtorotatethesymbolssothatthecarriersignalisalignedwiththefrequencyaxis.
Step5:Therotatedsymbolsarethendemodulatedagainusingthesoftdecisionstoproduceanewestimateofthecarrierphase.
Step6:Theiterati