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1、西安電子科技大學(xué)碩士學(xué)位論文LDPC碼迭代譯碼算法的研究姓名:孫冰申請(qǐng)學(xué)位級(jí)別:碩士專業(yè):通信與信息系統(tǒng)指導(dǎo)教師:張輝20090101摘要摘要低密度奇偶校驗(yàn)(LDPC)碼是一類可以提供逼近香農(nóng)容量限的線性分組碼,具有較好的誤碼性能和較低的錯(cuò)誤平層等諸多優(yōu)點(diǎn),碼長較長時(shí),甚至可以提供超過Turbo碼的誤碼性能。由于Turbo碼的發(fā)明以及LDPC碼的重新發(fā)現(xiàn),迭代譯碼這種技術(shù)受到了越來越多的關(guān)注。對(duì)于LDPC碼而言,盡管優(yōu)化的譯碼器可以提供很好的誤碼性能,但是由于其編譯碼算法的復(fù)雜度較高,在一定程度上限制了它在下一代數(shù)字通信和存儲(chǔ)系統(tǒng)的大規(guī)模應(yīng)用。本文在回顧了信道編
2、碼的基本知識(shí)和發(fā)展歷史之后,詳盡地介紹了LDPC碼的定義及其圖模型表達(dá),并且分析了現(xiàn)有的LDPC碼的構(gòu)造方法。接下來,本文詳細(xì)闡述了比特翻轉(zhuǎn)(BF)類譯碼以及置信傳播(BP)類譯碼這兩大類不同的譯碼算法前者可以實(shí)現(xiàn)非常低的譯碼復(fù)雜度,而后者可以達(dá)到最優(yōu)化的誤碼性能。具體介紹了包括比特翻轉(zhuǎn)(BF),加權(quán)比特翻轉(zhuǎn)(WBF),改善的加權(quán)比特翻轉(zhuǎn)(m忸F),經(jīng)典和積算法,對(duì)數(shù)域的和積算法等若干種當(dāng)前比較被廣泛接受的譯碼算法并給出了我們的仿真實(shí)驗(yàn)結(jié)果。最后,本文介紹了MIWBF、RRWBF、MMS、FMS和OMS等較新的譯碼算法,然后在前人的基礎(chǔ)上,提出了PIWBF、FB
3、F和LMMS等改進(jìn)的LDPC迭代譯碼算法,并且通過仿真實(shí)驗(yàn)說明了這些算法在實(shí)際譯碼應(yīng)用中可以帶來優(yōu)點(diǎn)。關(guān)鍵詞:低密度奇偶校驗(yàn)碼迭代譯碼比特翻轉(zhuǎn)算法置信傳播算法AbsmsctAbstractLOw-densityparity-check(LDPC)codesisaclassoflinearblockcodewhichcouldprovidenearShannon—Limitperformanceaswellaslowerror-floor.ForsomelongLDPCcodes,theirperformancesareevenbetterthentheTurbo
4、code.IterativedecodingtechniqueshavebeenreceivingmoreandmoreattentionswiththeinventionofturbocodesandtherediscoveryofLDPCcodes.AlthoughtheoptimumdecodingalgorithmscouldprovideverygoodperformanceforLDPCcodes,complicatedoperationsareinvolvedintheoptimumdecoding,andprohibitthewideapplic
5、ationsofLDPCcodesinthenextgenerationdigitalcommunicationandstoragesystem.Inthispaper,wereviewedthefundamentalknowledgeandrisinghistoryofthechannelcoding.WedescriptthecharacterizationofLDPCcode,showedhowtoexpressitasaTannerGraphanddiscussedhowtomakeagoodLDPCcodefrommanyaspects.Then,we
6、expoundedtwofamiliesofiterativedecodingalgorithmforLDPCcodes,oneisbit—flippingalgorithmwhichenablesverylowcomplexityindecoding,theotherisbeliefpropagationalgorithmwhichcouldreachverygoodperformance.WeconcretelyintroducedBF,WBF,IWBF,SPA,Log-SPAandanalyzedthembysimulatingtheirperforman
7、ce.Atlast,weintroducedseverallatelyandbetterwayofLDPCdecodingalgorithmsincludingMIWBF,RRWBF,MMS,F(xiàn)MS,OMS,andproposedseveralnewalgorithmslikePIWBF,FBFandLMMS,whichcouldenablelessiterationorreachhigherperformancewhilestillkeeplowcomplexity.Keyword:LDPClterativedecodingBit—flippingBelief
8、Propagation西