基于LDPC码的协作通信系统及联合迭代译码性能的研究

南京航空航天大学硕士学位论文基于LDPC码的协作通信系统及联合迭代译码性能的研究姓名：陈婧文申请学位级别：硕士专业：通信与信息系统指导教师：仰枫帆20090201I(MIMO)MIMO1.ShannonShannon2.LDPCTurbo3.BPLDPCBP4.LDPCLDPC5.LDPCLDPCLDPCLDPCTurboLDPCTannerTannerTurboLDPCIILDPCLDPCLDPCBPIIIAbstractWiththerapiddevelopmentofwirelesscommunications,theresearchofcooperativecommunicationtechnologyarousesmoreandmorepeople’sattention.Theconceptoftheso-calledcooperativecommunicationswasoriginallyproposedbasedonthetheoryofrelaychannelsandMIMOtechnique.)Inthisnewtechnique,thecooperativeuserscanachievethebenefitsfromdiversitythroughasignalingschemethatallowsthemtosendtheirinformationusingbothoftheirantennas,justlikeavirtualMIMOsystem.Therearebasicallythreemethodsforusercooperationstrategy:amplify-and-forward,detect-and-forwardandcodedcooperations,respectively.Morespecifically,inthecodedcooperation,theusersemploychannelcodingtoavoidtransmittingerroneousdatafortheirpartners.Asaresult,itachievesmuchbetterperformancethantheothertwosignalingschemes.Thisthesisisorganizedasfollows:1.UnderstandtheimportanceofthephenomenalShannonlimitforcapacityofnoisychannelandrevisitthe60-year(1948-2008)greatdiscoveriesinShannontheorysinceitsbirth.2.StudytheencodinganddecodingprinciplesofturboandLDPCcodes.ThenapplythetwocodingschemestostaticimagetransmissionsystemoveranAWGNchannel.ThesimulationresultsandBERperformancesaregiventoevaluatethequalityoftheimagetransmissions.3.InitiallyproposetwomodifiedBPalgorithmsrelatedtoverticalandhorizontalprocessinordertoaccelerateiterativeLDPCdecodingoveranAWGNchannel,wherethenewlyupdatedextrinsicinformationisimmediatelyusedinthecurrentdecodinground.TheoreticalanalysisandsimulationresultsdemonstratethatbothmodifiedapproachesprovidesignificantperformanceimprovementsoverthetraditionalBPalgorithmwithalmostnoadditionaldecodingcomplexity.Theproposedalgorithmwithmodifiedhorizontalprocessoffersevenbetterperformancethananotheralgorithmwithmodifiedhorizontalprocess.TwomodifiedBPalgorithmsareverypromisinginpracticalcommunicationssincebothcanachieveanexcellenttrade-offbetweentheperformanceanddecodingcomplexity.4.ProposeacooperativecommunicationschemebasedonregularLDPCcodesandjointdecodingovertherelaychannel.Inthefirststageofdecoding,twodecodersatthedestinationnodedecodetheirownreceivedsymbols,andthenoutputthecorrespondingsoftdetectioninformationseparately.Intheprocessofjointdecoding,twosetsofsoftinformationfromtherespectivedifferentdecoders,whicharecomplementarywitheachother,areincorporatedintoonestepofsignalestimation.ThisLDPCIVjointdecodingachievesthecodinggainsfromtheemployedLDPCcodesandthediversitygainsfromthecooperativestrategy.5.Initially,weproposeanothercooperativecommunicationschemebasedonthisnewlydesignedirregularLDPCcodeovertherelaychannel.Firstly,anewkindofsystematicirregularLDPCcodedisconstructed,andthencompareitsperformancewiththatofaregularLDPCcodeunderbasicallythesameconditions.Intheencodingstageofthecooperation,twodifferentirregularLDPCcodeswiththesamestructuralparametersareappliedtothesourceandrelay,respectively.Thedifferentcodesemployedimplytheresultedtwoparity-checksequenceswithlowercorrelation,whichisquitesimilarasaturbocodewiththestrategyofinterleaving.Inthedecodingstageofthecooperation,thejointiterativedecodingiseffectivelyperformedbasedonanincorporatedTannergraphformedbytwoconstructedsystematicirregularLDPCcodesinparallelconcatenation.Theprincipleofthisjointiterativedecodingissimilarasthatofiterativeturbodecodinguponthestrategyofextrinsicinformationthatfeedbacksfromtheparallelconstituentdecoders.AlthoughanirregularLDPCcodemayperformworsethanaregularLDPCcode,themeritsofcooperationbenefitthesystemperformancealot.Comparedwiththeformerone,thiscodedcooperationschemeincreasestheoverallcoderateandgreatlyimprovestheeffectivenessofthejointiterativedecoding.Keywords:cooperativecommunications,relaychannel,codedcooperation,LDPCcode,BPalgorithm,jointiterativedecodingLDPCXII1.1.........................................................................................................12.1ε-......................................................................................................182.2............................................................................................................182.3............................................................................................................182.4(BSC)........................................................................................182.5..............................................................................................................................242.6212...................................................................................................252.7(a)212......................................................................252.7(b)212..................................................................................262.8212.......................................................................................272.9Shannon.......................................................................292.101/2Tu