失配序列及其在DSCDMA系统中的应用研究

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1、西南交通大学硕士学位论文失配序列及其在DS-CDMA系统中的应用研究姓名：周英凤申请学位级别：硕士专业：通信与信息系统指导教师：彭代渊20080501西南交通大学硕士研究生学位论文第1I页AbstractSpreadspectrumcommunicationmodulatestheinformationdatawithspreadingsequences，andthentransformsthemodulatedsignalwithamuchwiderbandwidth，atthereceiver,afterdemodulati

2、onandcorrelationprocessingwiththesamespreadingsequences，thetransmittedinformationdatacanbegettedbackexactly．Onthebasisofthis，codedivisionmultipleaccess(CDMA)communicationsystemtakesadvantageoforthogonalspreadingsequencestodifferentiateusers．Themorethenumberofspreadin

3、gsequencessatisfyingthischaracter,themorethenumberofusers，viz．thecapacityofsystemislarger．ThereforeitisimportantforimprovingtheperformanceofdirectsequencespqeadspectrumCDMA(DS-CDMA)systemtoapplythesequenceswithgoodcorrelation，heregoodindicatesbigmainpeakofauto-correl

4、ationfunction，smallsidelobeofauto-correlationfunctionandsmallcross．correlationfunction．Atpresent，thewidely-usedspreadingsequencesincludemsequence，Goldsequence，etc．Butthemainshortageofthesespreadingsequencesisthattheyexistonlyatsomegivenlengthandthenumberofexistingseq

5、uencesislimited，whichrestricttheirapplicationsinpractice．However,themismatchedsequencestudiedinthispaperexistatmuchmorelengths，whichprovidemorechoiceforpracticalapplications．Somismatchedsequencecanmakeuptheshortageoftheactualspreadingsequencesasaneffectivesupplement．

6、Furthermore，applyingmismatchedsequencetotheCDMAcommunicationsystemputsforwardanewconceptandidea，viz．frommismatchedpointofview,tostudyoptimalsignal，whichismoreimportant．Inthispaper,firstly,theoptimalmismatchedsequencesetssatisfyingcertaingivenconditions，includingzeros

7、idelobeandlowcorrelationzone，aregenerated；Secondly,analyzetheirpropertiesofauto·-correlationandcross-．correlationandsomeresultswithbettercorrelationfunctionthanGoldsequencearefound；ThenmismatchedsequenceisappliedtoDS—CDMAcommunicationsystem，theBERperformanceofwhichis

8、studiedbyexpedmentalsimulationandafterwardsiscomparedwithGoldsequenceDS—CDMAcommunicationsystem，theresults西南交通大学硕士研究生学位论文第1II页_____