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1、蘭州交通大學(xué)畢業(yè)設(shè)計(jì)(論文)OFDM頻率偏移估計(jì)算法分析摘要作為一種特殊的多載波調(diào)制技術(shù),正交頻分復(fù)用(OFDM,OrthogonalFrequencyDivisionMultiplexing)因其高頻譜利用率、高數(shù)據(jù)傳輸速率以及良好的抗多徑干擾性能,廣泛地應(yīng)用于數(shù)字音視頻廣播、無線局域網(wǎng)等高速數(shù)據(jù)傳輸系統(tǒng)中。OFDM通信系統(tǒng)具備所有這些優(yōu)勢(shì)的前提是收發(fā)兩端子載波均要保持良好的正交性,然而,在實(shí)際應(yīng)用中,晶振的非理想因素以及移動(dòng)通信中多徑信道產(chǎn)生的多普勒頻移將會(huì)造成OFDM系統(tǒng)發(fā)射機(jī)與接收機(jī)載波中心頻率的偏移(CFO,C
2、arrierFrequencyOffset),而這將嚴(yán)重破壞子載波之間的正交性,因此OFDM系統(tǒng)接收機(jī)必須對(duì)載波頻偏加以估計(jì)并對(duì)接收信號(hào)進(jìn)行相應(yīng)補(bǔ)償以保證解調(diào)數(shù)據(jù)的準(zhǔn)確性。通常,將這一操作稱為載波頻率同步,也可簡(jiǎn)稱為頻偏估計(jì)。由于OFDM系統(tǒng)對(duì)CFO非常敏感,微小的CFO就能造成系統(tǒng)誤碼性能的大幅下降,因此,頻率同步技術(shù)是OFDM系統(tǒng)的關(guān)鍵技術(shù)之一。本論文首先回顧了OFDM技術(shù)發(fā)展的歷史,然后從基本的OFDM系統(tǒng)的原理出發(fā),闡述了OFDM系統(tǒng)中的同步問題。接著詳細(xì)闡述了定時(shí)同步偏差和載波頻率偏差對(duì)系統(tǒng)性能的影響。最后,對(duì)
3、現(xiàn)有的頻率同步技術(shù)(即,盲同步算法和非盲同步算法)進(jìn)行了介紹且重點(diǎn)介紹了三種具有代表性的載波頻偏估計(jì)算法:子載波間干擾(ICI,Intercarrierinterference)自消除方法,高階子載波間干擾(ICI)自消除方法和頻率偏移盲估計(jì)方法,并通過仿真比較分析了它們?cè)诩有愿咚拱自肼曅诺篮皖l率選擇性信道下的估計(jì)性能。關(guān)鍵詞:正交頻分復(fù)用;載波頻率偏移;子載波間干擾;盲載波頻偏估計(jì);自消除II蘭州交通大學(xué)畢業(yè)設(shè)計(jì)(論文)ABSTRACTAsaspecialmulticarriermodulationtechniqueO
4、FDM(OrthogonalFrequencyDivisionMultiplexing)hasbeenwidelyusedindatatransmissionsystemssuchasDigitalVideo/AudioBroadcastingsystemsandwirelessLANsystems,duetoitshighspectralefficiency,highdatarate,andexcellentperformancetocombatwithmulti-pathinterference.Itistheort
5、hogonalitybetweenthesub-carriersinOFDMsystemsthatguaranteesallthosestrengthsmentionedabove.However,thecarrierfrequencyoffset,causedbythenon-idealfactorsoftheoscillatorsandtheDopplerShiftintroducedbythemultipathchannel,willdestroytheorthogonalitybetweenthesubcarri
6、ers.Inordertogetabetterperformance,thereceivershouldestimatethecarrierfrequencyoffsetandthencompensatethereceivedsignal,whichisusuallycalledascarrierfrequencysynchronizationorfrequencyoffsetestimationforshort.OFDMsystemsareverysensitivetocarrierfrequencyoffset,th
7、atistosay,asmallfrequencyshiftcoulddegradethesystemperformancedramatically.Therefore,frequencysynchronizationtechniquehasbecomeoneofthekeytechniquesofOFDMsystems.Firstly,thisdissertationreviewsthehistoryofthedevelopmentofOFDMtechnique.AccordingtothebasicOFDMtheor
8、y,thisdissertationdescribessynchronizationofOFDMsystems.Then,describestheeffectofthetimingoffsetandfrequencyoffsettothesystemindetail.Finally,thefrequencysynch