简介:Coexistenceandinteroperabilitybetween20MHzand40MHzdeviceandmodesofop-erationsarestressedinstandardIEEE802.11nsystem.Itismandatetoreportthebothsub-channelsstatestoMediumAccessControl(MAC)atreceiver,sincefor40MHzdevice,itshouldservenotonly20MHzbutalso40MHzsignalsreceiving.Bothenergydetectionandcarriersenseareemployedtodetectchannelstate.Inthecaseof20/40Mmode,thepowerdifferencebetweenthetwosub-channelsisalsodetectedinordertoreportthechannelstateaccurately.Thesimulationresultsdemonstratethattheperformanceoftheproposedmethodsaremuchbetterthanthemethodswhichjustemployenergydetection.Besides,thesimulationresultsshowthattheproposedmethodsensurethatthechannelsensingisnotaroadblockofIEEE802.11nsystemdesign.
简介:单个标志最大可能性的(ML)可译码的时空块代码(SSDC)能完成6/7的最大的标志率为多重输入多重产量(MIMO)有五或六的通讯系统由使用率有效的概括坐标播送天线交叉直角的图案(RE-GCIODs)。不幸地,在RE-GCIODs的codeword矩阵有许多零个条目。零个条目导致高peak-to-average力量比率(PAPR)并且也在硬件实现上强加严重限制。在这份报纸,为有五或六的系统播送的MIMO通讯,天线和天线收到天线,新SSDC被建议。由联合Alamouti代码和直角的时空块代码(OSTBC),象RE-GCIODs一样的理想的性质能被完成并且被导出,包括直到6/7,完整的差异和单个标志的MLdecodability的最大的标志率。而且由在codeword矩阵减少零个条目的数字,我们的建议代码的peak-to-average力量比率(PAPR)比RE-GCIODs低。当在平均力量限制下面执行几乎一样时,模拟结果证明建议代码在山峰力量限制下面超过RE-GCIODs。
简介:Ahybridpilotsassistedchannelestimationalgorithmformultipleinputmultipleoutput(MIMO)orthogonalfrequencydivisionmultiplexing(OFDM)systemsunderlowsignal-to-noiseratio(SNR)andarbitraryDopplerspreadscenariosisproposed.Motivatedbythedissatisfactoryperformanceoftheoptimalpilots(OPs)designedunderstaticchannelsovermultipleOFDMsymbolsimposedbyfastfadingchannels,theproposedschemefirstassumesthatthevirtualpilottonessuperimposedatdatalocationsoverspecificsubcarriersaretransmittedfromallantennas,thenthevirtualreceivedpilotsignalsatthecorrespondinglocationscanbeobtainedbymakingfulluseofthetimeandfrequencydomaincorrelationsofthefrequencyresponsesofthetimevaryingdispersivefadingchannelsandthereceivedsignalsatpilotsubcarriers,finallythechannelparametersarederivedfromthecombinationoftherealandvirtualreceivedpilotsignalsoveroneOFDMsymbolbasedonleastsquare(LS)criterion.SimulationresultsillustratethattheproposedmethodisinsensitivetoDopplerspreadandcaneffectivelyamelioratethemeansquareerror(MSE)floorinherenttothepreviousmethod,meanwhileitsperformanceoutmatchesthatofOPsatlowSNRregionunderstaticchannels.
简介:Inrealmultiple-inputmultiple-output(MIMO)systems,theperfectchannelstateinformation(CSI)maybecostlyorimpossibletoacquire.Butthechannelstatisticalinformationcanbeconsideredrelativelystationaryduringlong-termtransmission.Thestatisticalinformationcanbeobtainedatthereceiverandfedbacktothetransmitteranddonotrequirefrequentupdate.Byexploitingchannelmeanandcovarianceinformationatthetransmittersimultaneously,thispaperinvestigatestheoptimaltrans-missionstrategyforspatiallycorrelatedMIMOchannels.Anupperboundofergodiccapacityisderivedandtakenastheper-formancecriterion.Simulationresultsarealsogiventoshowtheperformanceimprovementoftheoptimaltransmissionstrategy.
简介:Recently,anewsoft-insoft-outdetectionalgorithmbasedontheMarkovChainMonteCarlo(MCMC)simulationtechniqueforMultiple-InputMultiple-Output(MIMO)systemsisproposed,whichisshowntoperformsignificantlybetterthantheirspheredecodingcounterpartswithrelativelylowcomplexity.However,theMCMCsimulatorislikelytogettrappedinafixedstatewhenthechannelSNRishigh,thuslotsofrepetitivesamplesareobservedandtheaccuracyofAPosterioriProbability(APP)estimationdeteriorates.Tosolvethisproblem,animprovedversionofMCMCsimulator,namedforced-dispersedMCMCalgorithmisproposed.Basedontheaposteriorivarianceofeachbit,theGibbssamplerismonitored.Oncethetrappedstateisdetected,thesampleisdispersedintentionallyaccordingtotheaposteriorivariance.Extensivesimulationshowsthat,comparedwiththeexistingsolution,theproposedalgorithmenablesthemarkovchaintotravelmorestates,whichensuresanear-optimalperformance.
简介:ThispaperdescribesaLeastSquares(LS)channelestimationschemeforMIMOOFDMsystemsbasedontime-domaintrainingsequence.Wefirstcomputetheminimummeansquareerror(MSE)oftheLSchannelestimation,andthenderivetheoptimalcriteriaofthetrainingsequencewithrespecttotheminimumMSE.Itisshownthatoptimaltime-domaintrainingsequenceshouldsatisfytwocriteria.First,theautocorrelationofthesequencetransmittedfromthesameantennaisanimpulsefunctioninaregionlongerthanthechannelmaximumdelay.Second,thecross-correlationbetweensequencestransmittedfromdifferentantennasiszerointhisregion.Simulationresultsshowthattheestimatorusingoptimaltime-domaintrainingsequenceshasbetterperformancethanthatusingoptimalfrequencytrainingsequenceatlowsignal-to-noiseratio(SNR).Toreducethetrainingoverhead,asuboptimaltrainingsequenceisalsoproposed.Comparingwithoptimaltrainingsequence,ithaslowcomputationcomplexityandhightransmissionefficiencyattheexpenseoflittleperformancedegradation.
简介:摘要:大规模多输入多输出(Massive MIMO)无线通信技术是当前无线通信领域的研究热点,它通过在基站部署大量的天线,以实现更高的系统吞吐量和更低的传输延迟。本文主要探究了大规模MIMO无线通信的关键技术,包括信道估计、波束成形、用户调度和资源分配等,分析了这些技术在大规模MIMO系统中的挑战和解决方案。
简介:摘要本文针对当前英语词汇输入时教师忽略词汇操练和运用这一现象,结合课堂教学实践,探讨了如何置学生于语境中理解词汇、操练词汇,从而使词汇学习从识记的层面内化成学生运用语言词汇的一种自觉、自如的习惯。在此基础上提出了基于语境下的ITT词汇输入模式,并辅以详实的个案来分析其操作过程,及ITT模式下词汇输入教学时所应该遵循的原则,希望对我们的教学有一定的借鉴作用。