small world communicationsnew

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1、TURBOCODES:atutorialonanewclassofpowerfulerrorcorrectingcodingschemesPartI:CodeStructuresandInterleaverDesignS.AdrianBarbulescu(adrian@spri.levels.unisa.edu.au)InstituteforTelecommunicationsResearchUniversityofSouthAustraliaStevenS.Pietrobon(steven@sworld

2、.com.au)SmallWorldCommunicationsRevised:26October1998AbstractThisisatutorialpapermeanttointroducethereadertothenewconceptofturbocodes.Thisisanewandverypowerfulerrorcorrectiontechniquewhichoutperformsallpreviousknowncodingschemes.Itcanbeusedinanycommunicat

3、ionsystemwhereasignificantpowersavingisrequiredortheoperatingsignal–to–noiseratioisverylow.Deepspacecommunications,mobilesatellite/cellularcommunications,microwavelinks,paging,etc.,aresomeofthepossibleapplicationsofthisrevolutionarycodingtechnique.PartIof

4、thepaperdiscussesthehistoryofturbocodes,whytheyaredifferentfromtraditionalconvolutional/blockcodes,turboencoderstructuresandissuesrelatedtotheinterleaverdesign.PartIIwilladdresstheturbodecoderarchitecture,theachievableperformanceforturbocodesforawiderange

5、ofcodingratesandmodulationtechniques,andwilldiscussdelayandimplementationissues.1IntroductionIncreasingdemandforinformationexchangeisacharacteristicofmoderncivilisation.Thetransferofinformationfromthesourcetoitsdestinationhastobedoneinsuchawaythatthequali

6、tyofthereceivedinformationshouldbeascloseaspossibletothequalityofthetransmitted1information.AtypicalcommunicationsystemmayberepresentedbytheblockdiagramshowninFigure1.1.InformationSourceErrorControlEncrypterModulatorSourceEncoderEncoderChannelInformationS

7、ourceErrorControlDecrypterDemodulatorSinkDecoderDecoderFigure1.1:Ablockdiagramofacommunicationsystem.Theinformationtobetransmittedcanbemachinegenerated(e.g.,images,computerdata)orhumangenerated(e.g.,speech).Regardlessofitssource,theinformationmustbetransl

8、atedintoasetofsignalsoptimisedforthechanneloverwhichwewanttosendit.Thefirststepistoeliminatetheredundantpartinordertomaximisetheinformationtransmissionrate.ThisisachievedbythesourceencoderblockinFigure1.1.Inordertoe