简介:Responseofadaptivematchedfilter,alsocalledadaptivecorrelator,tomultipathchannelisdiscussedinthispaper.Ithasbeenprovedthatthenewtypeprocessorcanbettermatchwithmultipathchan-nel.Theresultsofexperimentcarriedoutonlakeandinlaboratoryarepresented.Itshowsthattheprocessorhasgooddetectingperformanceintimedomain.
简介:Tostudythepossibilityofdetectingthecrossingchannelbyusingatraditionalloggingtool,acousticfieldgeneratedbyamonopolesourceinacasedwellwithacrossingchannelofvariousanglesissimulatedby2.5-DFiniteDifferenceMethod(FDM).Snapshotsofnormalstressandsynthetictime-domainwaveformsaredisplayed.Thetwo-dimensionalspectruminwave-numberandfrequencydomainsisalsocalculated,wheretheinfluenceofthechannelisclearerthanthatinthewaveforms.Numericalstudydemonstratedthatacrossingchannelcanbedetectedandsizedifitsangleisgreaterthan30degree,andlargerspacingandlowerfrequencysourcearefavorabletodetectandsizethecrossingchannel.
简介:Noncoherentunderwateracousticcommunicationchannelinadverseconditionsismodeledasaphase-randomRayleighfadingchannel,anditscapacitycurveisderived.Toapproachthechannelcapacitycurve,theconcatenatedcodeofthenonbinaryLDPCcodeandtheconstantweightcodeisproposedfornoncoherentcommunicationwhichcanlatebeiterativelydecodedintheprobabilitydomain.Withoutinformationofchannelamplitudeorphaseinthereceiver,statisticparametersoftherespectivesignalandnoisebinswereestimatedbasedonthemomentestimationmethod,theposteriorprobabilitiesoftheconstantweightcodewordswerefurthercalculated,andthenonbinaryLDPCcodewasdecodedwiththenonbinaryfactorgraphalgorithm.Itisverifiedbysimulationsthatbyutilizingtheproposedconcatenatedcodeanditsprocessingalgorithm,gaptochannelcapacitycurveisreducedby3dBwhencomparedtotheexistingmethod.Underwatercommunicationexperimentswerecarriedoutinbothdeepocean(verticalcommunication,5km)andshallowlake(horizontalcommunication,near3km,delayspreadlargerthan50ms),inwhichthesignalfrequencybandwas6kHzto10kHz,andthedatatransmissionrateWas357bps.Theproposedschemecanworkproperlyinbothexperimentswithasignal-to-noiseratiothresholdof2dB.TheperformanceoftheproposedalgorithmWaswellverifiedbytheexperiments.
简介:Theoreticalandexperimentalresearchoflowfrequencypulsecompressionandchannelmatchinshallowwatersoundchannelwerecarriedoutbasedon2000-WinterYellowSeaexperiment.Usingpulsecompressionmethod,signalswithhighsignaltonoiseratio(SNR)werereceivedoverrangeof110kilometersintheexperiment.TheSNRgainintheprocessisconsistentwiththetheoreticalprediction.Theexperimentalmeasurementindicatedthatthechannelishighlycoherentoveralengthof500s.ChannelmatchmethodwasusedtocompensatethedegradationofpulsecompressionSNRcausedbythemulti-pathpropagation.AndtheSNRgaininthechannelmatchprocesscanbetheoreticallypredicted.ExperimentalresultsshowthatlowfrequencypulsecompressionandchannelmatchmethodcanbeusedinshallowwatersoundchanneltoimprovetheSNR.
简介:Inthispaper,theoceanacousticchannelisconsideredasatime-variantchannel.Inordertoanalysetheconjointtime-shift-fre-quency-delaydistributionorthefadingandspreadstatisticalcharacteristicsofthechannel.TheTDWVS(TwoDimensionalWigner-VilleSpectrum)ofthetime-variantchannelisdefined.TherelationbetweentheWVS(Wigner-VilleSpectrum)oftheinputandtheoutputofthechannelisdiscussedandsomeexamplesforthespecificchannelareshown.Finally,theapplicationsonthedetectionofsignalsinnoiseusingtheWVSandTDWVSaregivenandtheadvantageisobvious,whenthedetectedsignalislinearfrequency-modulationsignal.