简介：Aimingattheproblemofthepeaktoaveragepowerratio（PAPR）incoherentopticalorthogonalfrequencydivisionmultiplexing（CO-OFDM）,ahybridPAPRreductiontechniqueoftheCO-OFDMsystembycombiningiterativepartialtransmitsequence（IPTS）schemewithmodifiedclippingandfiltering（MCF）isproposed.Thesimulationresultsshowthatatthecomplementarycumulativedistributionfunction（CCDF）of104,thePAPRofproposedschemeisoptimizedby1.86dBand2.13dBcomparedwiththoseofIPTSandCFschemes,respectively.Meanwhile,whenthebiterrorrate（BER）is10^-3,theopticalsignaltonoiseratio（OSNR）areoptimizedby1.57dBand0.66dBcomparedwiththoseofCFandIPTS-CFschemes,respectively.

简介：Inthispaper,awavelengthdivisionmultiplexing(WDM)transmissionsystemderivedfromthecoherentopticalorthogonalfrequencydivisionmultiplexing(CO-OFDM)withpolarizationdivisionmultiplexing(PDM)and16-orderquadratureamplitudemodulation(QAM)isstudied.Asimulationof80-channelWDMtransmissionsystemwithdatarateof200Gbit/sisbuilt,andthetransmissionperformanceofthesystemisanalyzed.ThesimulationresultsshowthatthesystemQvalueoftheWDMchannelsat16Tbit/swithaspectralefficiencyof7.14bit/s/Hzispotentiallyover10.0dBforalonghaultransmissionupto1800kminastandardsingle-modefiber.

简介：Inthispaper,anewtimingoffsetestimationmethodforOrthogonalFrequencyDivisionMultiplexing(OFDM)systemsarepresented.Uponthereceiptofjustonetrainingsequence,thispresenceofasignalandthestartoftheframecanbedetected.TheperformancesofthetimingestimatorinadditivewhiteGaussiannoiseandthemobilemultipathchannelareevaluatedbysimulation.TheresultsdeliveredbythisalgorithmarecomparedwiththosedeliveredbySchmidlandCox.

简介：DiscreteFourierTransform(DFT)basedmultiple-inputmultiple-outputOrthogonalFrequencyDivisionMultiplexing(MIMO-OFDM)isthefocusofwirelesscommunication,whichusescyclicprefixestoreducetheISI.Toimprovethespectrumefficiencyandsystemperformance,ComplexWaveletPacketTransform(CWPT)basedOFDMisusedtorealizetheMIMO-OFDMsystem.Forthegoodpropertyofcomplexwaveletpacketfunction,theCWPTbasedMIMO-OFDMsystemisbetterthantheDFTbasedMIMO-OFDMsystem,buttheCWPTbasedMIMO-OFDMschemehassomeadditionalcomplexity,andsimulationresultsshowthatthenewsystemcanimprovethesystemperformance.

简介：一、OFDM简介在传统的多载波通信系统中，整个系统频带被划分为若干个互相分离的子信道，也就是所谓的载波。为了避免信道之间的干扰，在信道之间通常有一定宽度的保护间隔，接收端通过滤波器把各个子信道分离之后接收所需信息。这样虽然可以避免不同信道的互相干扰，但却以牺牲频率利用率为代价。而且当子信道数量很大的时候，大量分离各子信道信号的滤波器的设置就成了几乎不可能的事情。

简介：当前无线通信技术的发展，形成了移动通信宽带数据化和数据通信无线移动化两大趋势。受到这两大潮流的影响，WiMAX和Flash—OFDM技术的发展逐渐侵入了对方的领域，原本互补的关系也越来越多地掺杂进了竞争的成分。一方面，将于最近完成的802．16e标准将支持中低车速(<120km／h)下的移动应用和小区间切换，

简介：无线通信作为新兴的通信技术在日常生活中的作用越来越大。近年来，无线局域网技术发展迅速，但无线局域网的性能、速度与传统以太网相比还有一定距离，因此如何提高无线网络的性能和容量日益显得重要。

简介：OrthogonalFrequencyDivisionMultiplexing(OFDM)systemissensitivetoCarrierFrequencyOffset(CFO).Inthispaper,traditionalMaximumLikelihoodEstimators(MLE)forCFOofOFDMareintroducedfirst.Then,averagingmethodandα-filterareintroducedasLowPassFilter(LPF)toimprovetheperformanceofcyclicprefixestimator.ThebandwithofLPFisdeterminedbythecoherencetimeofradiochannel.Estimationperformanceinmultipathchannelisanalyzed.Outlierpicking-outschemeisproposedtoimproveperformancefurther.Performanceofclose-loopstructureispresentedbriefly,whichisworsethanthatofopen-loopstructure.Finally,aparallelswitchstructureoffrequencysynchronizerisproposedformobileOFDMsystems.Theschemeexploitstrainingsequenceandcyclicprefix.Theproposedsynchronizerhasawideacquisitionrange.ItisaccurateandrobustinbothAWGNchannelandmultipathchannels.Thecomplexityislowduetofunctionalityofα-filter.AbetterperformanceoffrequencysynchronizationisobtainedcomparingtothatofexistingMaximumLikelihoodEstimator(MLEs).Weachievetheseadvantageswithoutlossofbandwidthefficiency.

简介：OneoftheprincipaldisadvantagesofOrthogonalFrequencyDivisionMultiplexing(OFDM)isverysensitivetocarrierfrequencyoffset.Theintegerfrequencyoffsethasnoeffectontheorthogonalityamongthesubcarriers,butitcausesacircularshiftandphaserotationofthereceiveddatasymbolssequence,resultinginaBitErrorRate(BER)of0.5.Inthispaper,anovelintegerfrequencyoffsetestimatorforOFDMisderivedbasedonmaximumlikelihoodestimationtechniqueandexplorationofthedifferentialrelationbetweentwoconsecutiveOFDMdatasymbolsequencesinfrequencydomain.ItsperformanceiscomparedwiththeconventionalmethodbycomputersimulationsfortheadditivewhiteGaussiannoisechannelandamultipathfadingchannel.Simulationresultsshowthattheperformanceoftheproposedestimatorisbetterthantheconventionalestimator.

简介：Athresholdsettingschemeisproposedbasedontheresourcemanagementandlimitedfeedbacktheoryinmultiuserorthogonalfrequencydivisionmultiplexing(OFDM)systems.Inadaptiveresourceallocation,thefactorsdenotingthequalityofservice(QoS)andfairnessarebothconsideredastheuserweight.Fromtheaspectoffeedbackoutageprobability,theproposedalgorithmsetsthethresholdforeachuserrelatedtoitsweight,whichbringsenoughfeedbacktotheuserwithgreaterweight.Analysisandsimulationresultsshowthat,comparedwiththethresholdignoringweights,theproposedschemehasmuchlowerfeedbackloadwhilewithbetterQoS.

简介：本文详细介绍了基于超宽带（UWB）技术的双载波正交频分复用（DC—OFDM）系统中的一种符号同步算法，该算法把整个符号同步过程分为四个步骤来实现：包检测、粗同步、时频编码（TFC）检测以及精细同步。在算法的实现上，本文采用了自相关和互相关的方法，以满足在不同的室内多径环境下UWB技术的要求，并且该算法具有很好的鲁棒性。

简介：在基于正交频分复用（OFDM）的认知无线电系统中,提出了一种旁瓣抑制的星座修整法,动态增大频域符号块中某些星座点的实部或虚部来抑制OFDM信号在目标频段内的旁瓣。将旁瓣抑制的星座修整法建模为二阶约束二阶规划（QCQP）问题,从而获取最优解。仿真结果表明,该方法可以获得良好的旁瓣抑制效果。

简介：Inthispaper,ablockwiseadaptivesubcarrierallocationalgorithmformultiuserOrthogonalFrequencyDivisionMultiplexing(OFDM)systemisintroduced.Assumingtheknowledgeofchannelinformationforallusers,thealgorithmminimizesthetotaltransmitpowerwhilesatisfyingthetotalpowerandusers'rateconstraints.TheresultofsimulationshowsthattheproposedalgorithmreducestheaveragebitSignal-to-NoiseRatio(SNR)byapproximately4dBcomparedwithOFDM-FrequencyDivisionMultipleAccess(OFDM-FDMA),andsupportsmoreusersinamultiuserRayleighfadingchannel.Asassigningsubcarriersinblock,thecomputationalcomplexityofthealgorithmismuchlowerthanthatofthederivationof"water-filling"algorithm.

简介：介绍了当前3G成熟的CDMA技术和未来4G的核心技术OFDM的基本原理和各自优缺点，分析了CDMA和OFDM两种不同技术的应用侧重，同时指出了两种技术融合的前景及前沿拓展。

简介：Inthispaper,thefeedbackloadreductionprobleminwirelesssystemsbasedonorthogonalfrequencydivisionmultiplexing(OFDM)isinvestigatedandanopportunisticfeedbackscheme(OFS)isproposed.ThekeyideabehindOFSisthatonlythekeychannelgainswhichcansignificantlyaffectthesystemthroughputarefedbacktotheBS.Firstly,thekeychannelgainsareprovedtobelongtoachannelgaininterval.Secondly,astatisticalmethodisproposedtoestimatethechannelgaininterval.Thirdly,theopportunisticfeedbackschemeisformulatedandthefeedbackloadofOFSisanalyzed.TheadvantageofOFSisthreefold:thefirstisOFScanworkinbothOFDM-basedmulticastsystemandOFDM-basedunicastsystem.ThesecondisthechannelfadingtypeoftheBS-userlinkisnotrequired,whichismorerealistic.ThethirdisOFScangetbetterfeedbackloadperformancecomparedwithotherschemes,whileachievingalmostthesamethroughputperformancecomparedwiththatoffullfeedbackscheme.

简介：Ananti-interferenceorthogonalcodingisintroducedbasedonHadamardcodeandOrthogonalFrequency-DivisionMultiplexing(OFDM),inwhichallsub-channelsofUltra-WideBand(UWB)systemaredividedintoMsub-bandsandthepoweroftheeverytransmittedsymbolspreadsovereachofthesub-bandsratherthanonesub-band.Thecompletemathematicalanalyticalrelationbetweenencodinganddecodingispresentandtherobustnessofthesystemtointerferenceisexamined.Whensomesub-channelsareaffectedbyinterferenceorjamming,thesystemcouldregeneratethesymbolfromothers.SimulationresultsshowthattheAnti-InterferenceUWB-OFDM(AI-OFDM)systemhasevidentadvantagesoverconventionalUWB-OFDMsystemsaswellastheInterferenceSuppressingUWB-OFDM(IS-OFDM)inBitErrorRate(BER)thankstoitsrobustnesstointerference.Inthecaseofbadinterference,theAI-OFDMsystemcouldworkuptosnuffwithoutanyanti-interferencestep,buttheconventionalUWB-OFDMsystemcouldn't.ComparedwiththeIS-OFDMsystem,theAI-OFDMsystemimprovestheperformanceabout5dBinSignal-to-InterferenceRatio(SIR)andtheorderof1～2inBER.

简介：Theresearchandapplicationofwirelesslocalareanetworks(WLAN)technologyareinastageofrapiddevelopment.Ithasbeenoneofresearchfocusesofthewirelesscommunicationsfield.Throughtheuseofenhancedsingle-user(SU)/multi-user(MU)multipleinputmultipleoutput(MIMO)-orthogonalfrequencydivisionmultiplexing(OFDM)technology,thenextgenerationWLANIEEE802.11acdramaticallyincreasesthethroughput.AnimprovedMIMO-OFDMschemebasedonmodulationdiversityisproposedforthenextgenerationWLAN.Itusestwo-dimensionalmodulationdiversitytothecurrentIEEE802.11actransmissionscheme.Throughthespace-time-frequencycomponentinterleaverandtherotationalmodulation,theproposedschemeexhibitshighspectralefficiencyandlowerrorrateinfadingchannels.ThesimulationresultsshowthattheproposedschemesignificantlyoutperformstheSU/MUMIMO-OFDMschemeinthecurrentIEEE802.11acstandard,whichisupto5dB.

简介：短波通信是远距离信息传输的重要手段,OFDM（正交多载波调制）是一种在无线环境下具有较高频谱利用率的多载波调制技术。将OFDM技术应用于短波通信中,搭建了OFDM的试验平台,建立了短波通信链路,对接收端采集的基带OFDM信号进行了处理。通过编码和信道估计分别对信号进行纠错和信道补偿,处理结果表明,在传输速率600b/s下系统的误比特率达到10^-5数量级,系统性能良好。

简介：文章对高速载波调制解调技术原理及其实现技术进行了研究,并根据MIL-STD-1553A/B实际传输的硬件系统,建立信道模型及噪声模型。该系统由基带信号处理和线缆驱动两部分组成,通过对传输系统中各处理模块的分析,并利用MatlabSimulink仿真平台进行系统级仿真,仿真结果表明OFDM调制解调技术获得10-5较低的误码率,可应用于已有的1553总线这样的高速有线传输系统。

简介：由于MIMO雷达发射相互正交的波形，因此正交波形设计是MIMO雷达实现的关键问题。针对MIMO雷达发射波形正交的特点，介绍了正交频分复用线性调频波形（OFDM—LFM）的设计原理。提出了一种正交频分线性调频波形产生的实现方案，该方案通过并行发射多路频分的线性调频信号形成OFDM—LFM波形。设计了一种由主控计算机、波形控制模块和数字中频合成模块构成的OFDM—LFM波形产生器。给出了基于AD9910数字斜坡调制方式产生单通道线性调频信号的方法和0sK功能产生多通道线性调频脉冲信号的方法，并对单通道线性调频信号线性度进行了分析。最后给出了其中两通道LFM信号频谱和一通道线性调频脉冲信号的时域波形的测试结果，验证了方案的正确性和可行性。