The mitigation of co-channel interference (CCI) and inter-symbol interference (ISI) has been a major area of focus of researchers in wireless communications. An approach of interest separates CCI cancellation and ISI equalization in a slow frequency-select

JointCo-channelInterferenceCancellationandChannel

ShorteningwithSpace-TimeProcessing

RoopshaSamanta

LiteratureSurvey

MultidimensionalDigitalSignalProcessing

WirelessSystemsInnovationsLaboratory

TheUniversityofTexasatAustin,TX78712

roopsha@ece.utexas.edu

Spring2003

Abstract

Themitigationofco-channelinterference(CCI)andinter-symbolinterference(ISI)hasbeenamajorareaoffocusofresearchersinwirelesscommunications.AnapproachofinterestseparatesCCIcancellationandISIequalizationinaslowfrequency-selectiveRayleighfadingchannelintotwostages.Aspace-time lterreducestheCCI,followedbyaViterbiequalizerforISIequalization.ThecomplexityoftheViterbiequalizercanbereducedbyusinga lterforchannelshortening.Iaminvestigatingvariouswaystodesignaspace-time nite-impulseresponse(FIR) lterwhichwouldperformjointCCIcancellationandchannelshortening,whilemaximizingasignal-to-interference-plus-noise-likeobjectivefunction.

The mitigation of co-channel interference (CCI) and inter-symbol interference (ISI) has been a major area of focus of researchers in wireless communications. An approach of interest separates CCI cancellation and ISI equalization in a slow frequency-select

1Introduction

Co-channelinterference(CCI)isaprobleminherenttoallcellularwirelesscommunicationsys-tems.Itarisesduetothebasicfrequencyreuseschemeofcellularsystems.Thismeansthatanumberofcellsinagivencoverageareausethesamesetoffrequencies.Theinterferencebetweenthesignalsfromthesecellsistermedasco-channelinterference.Inter-symbolinterference(ISI)isacharacteristicproblemoffrequency-selectivefadingchannels.Themultipleversionsofthetransmittedwaveform,whichtravelovermultiplere ectivepaths,arriveatslightlydi erenttimesfromtheothers.Thisleadstoaspreadingofthesymbolintime(timedispersion).Someofthesecomponentsarriveduringthenextsymbolduration,causingISI(commonlytermedaschannel-inducedISItodi erentiateitfromtheISIcausedby lters).[1]and[2]arecomprehensivetutorialsonthecharacterizationandmitigationoffadinganditse ectsinmobileRayleighfadingchannels.

ThemitigationofbothCCIandISIhasbeenamajorconcernofresearchersinwirelesscommuni-cations.Thegoalhasbeentodemodulatethedatasymbolswhilemaximizingthesignal-to-interference-plus-noiseratio(SINR),usingequalizersofacceptablecomplexity.

Theareademandsatrade-o betweentheSINRandthecomplexityofthereceiverandtheoptimumsolutionstillremainsanopenproblem.

2Background

VariousapproachestodealwithCCIandISIequalizationhavebeensuggestedovertheyears.Amulti-user-maximum-likelihood-sequence-estimator(MLSE)[3]istheoptimalsolutionformaximizingthesignal-to-interferenceratio(SIR).Butitrequiresthechannelinformationoftheinterfereralongwiththatofthedesireduserandthiscannotbeeasilyestimated.

Whiletherehavebeensubsequentsub-optimalsolutionstotheproblem,oneapproachofinteresthasbeenpresentedbytheauthorsin[4].ThispaperisdiscussedinSection3.Itisbasicallyasingleusertwo-stageapproachforseparateCCIreductionandISIequalizationinaslowfrequency-selectiveRayleighfadingchannel.Aspace-time lterisusedforCCIcancellationinthe rststage.AViterbi

The mitigation of co-channel interference (CCI) and inter-symbol interference (ISI) has been a major area of focus of researchers in wireless communications. An approach of interest separates CCI cancellation and ISI equalization in a slow frequency-select

equalizerperformsISIequalizationinthesecondstage.Thecomplexityofthisequalizerisafunctionofthenumberofstatesinit,whichinturn,isanexponentialfunctionofthelengthofthechannelimpulseresponse.In[4],thecomplexityoftheequalizerisnotaddressed.

Ahelpfulreferenceforequalizerdesignforcellularmobileradiochannelsis[5].Here,theauthorshavepresentedacomprehensivetheoryforoptimumdiversitycombiningandequalizationindigitaldatatransmissionoverfrequency-selectiveRayleighfadingchannels.Variouscombiner-equalizers,whichminimizethemean-squarederror,aredetermined.

Auni edanalysisofoptimumspace-timeequalizerswithlinear ltersoneachantennabranch,followedbyadecisionfeedbackequalizer(DFE)orMLSEisprovidedin[6].

Channelshorteningfordiscretemulti-tone(DMT)transceiversisamuch-researchedareaand

[7]exploresvariousmethodsfordeterminingthecoe cientsofatime-domainchannelshortening lter.VariousrelevantreferencesforchannelshorteningareexploredinSection4.

ChannelmemorytruncationforreducingthecomplexityoftheViterbidecoderwassuggestedasearlyas1973in[8],[9]and1978in[10].Thedi erentapproachestothisproblemarediscussedandcomparedinSection5.

3CCI/ISIReductionwithSpace-TimeProcessing

ThispaperpresentsahybridapproachforseparateCCIreductionandISIequalizationinaslowRayleighfadingchannel.Thesignalisreceivedbyanarrayofantennas,followedbyaspace-time lterasshowninFigure1.The lterisdesignedtomaximizethesignal-to-interference-plus-noiseratio(SINR)byjointlyoptimizingthe ltersweightvectorandthemodi edchannelvector(e ectivechannelimpulseresponse).ThischannelvectorisusedbyaViterbiequalizer,thatformsthenextstage,todemodulatethedatasymbolswithISIequalization.

Thespace-time lterhasthee ectoftemporallycoloringthedisturbance.TheViterbialgorithmperformsoptimallyonlywhentheinputnoiseiswhite.So,atemporalwhitening lterisincludedinthedesignoftheViterbiequalizertotakecareofnon-GaussianresidualCCIandnoise.

The mitigation of co-channel interference (CCI) and inter-symbol interference (ISI) has been a major area of focus of researchers in wireless communications. An approach of interest separates CCI cancellation and ISI equalization in a slow frequency-select

TheauthorsdonotrelyonthechannelinformationofCCI.Atrainingsequenceisusedbythejointoptimizertoprovideaneigenvectorsolutionforthespace-time lte …… 此处隐藏：12139字，全部文档内容请下载后查看。喜欢就下载吧 ……