基于MIMOOFDM系统的正交空时分组码+单位抗衰落复正交空时分组码级联的Turbo码毕业论文外文翻译.docx
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基于MIMOOFDM系统的正交空时分组码+单位抗衰落复正交空时分组码级联的Turbo码毕业论文外文翻译
外文资料
(一)
OnOrthogonalSpace-TimeBlockCodesfor
MIMO-OFDMSystems
Space-timecodeinmobilecommunicationsystem,andorthogonaldesinginmultiple-antennasscnemearedicsussed.Bythemethods,dataisencodedusingaspace-timeblockcodeandissplitintoseveralstreamswhicharesimultaneouslytransmittedbyantennas.Soamaximum-likelihooddecodingalgorithmcanbeusedatthereceivertoachievethemaximumdiversityorder
Introduction
Mostworkonwirelesscommunicationshadfocusedonhavinganantennaarrayatonlyoneendofthewirelesslink—usuallyatthereceiver.SeminalpapersbyGerardJ.FoschiniandMichaelJ.Gans[1],Foschini[2]andEmreTelatar[3]enlargedthescopeofwirelesscommunicationpossibilitiesbyshowingthatforthehighly-scatteringenvironmentsubstantialcapacitygainsareenabledwhenantennaarraysareusedatbothendsofalink.Analternativeapproachtoutilizingmultipleantennasreliesonhavingmultipletransmitantennasandonlyoptionallymultiplereceiveantennas.ProposedbyVahidTarokh,NambiSeshadriandRobertCalderbank,thesespace–timecodes(STCs)achievesignificanterrorrateimprovementsoversingle-antennasystems.TheiroriginalschemewasbasedontrelliscodesbutthesimplerblockcodeswereutilizedbySiavashAlamouti,andlaterVahidTarokh,HamidJafarkhaniandRobertCalderbanktodevelopspace–timeblock-codes(STBCs)[4].STCinvolvesthetransmissionofmultipleredundantcopiesofdatatocompensateforfadingandthermalnoiseinthehopethatsomeofthemmayarriveatthereceiverinabetterstatethanothers.InthecaseofSTBCinparticular,thedatastreamtobetransmittedisencodedinblocks,whicharedistributedamongspacedantennasandacrosstime.Whileitisnecessarytohavemultipletransmitantennas,itisnotnecessarytohavemultiplereceiveantennas,althoughtodosoimprovesperformance.ThisprocessofreceivingdiversecopiesofthedataisknownasdiversityreceptionandiswhatwaslargelystudieduntilFoschini's1998paper.
AnSTBCisusuallyrepresentedbyamatrix.Eachrowrepresentsatimeslotandeachcolumnrepresentsoneantenna'stransmissionsovertime.
Here,sijisthemodulatedsymboltobetransmittedintimeslotifromantennaj.TherearetobeTtimeslotsandnTtransmitantennasaswellasnRreceiveantennas.Thisblockisusuallyconsideredtobeof'length'T
ThecoderateofanSTBCmeasureshowmanysymbolspertimeslotittransmitsonaverageoverthecourseofoneblock.Ifablockencodesksymbols,thecode-rateis
OnlyonestandardSTBCcanachievefull-rate(rate1)—Alamouti'scode
Orthogonality
STBCsasoriginallyintroduced,andasusuallystudied,areorthogonal.ThismeansthattheSTBCisdesignedsuchthatthevectorsrepresentinganypairofcolumnstakenfromthecodingmatrixisorthogonal.Theresultofthisissimple,linear,optimaldecodingatthereceiver.Itsmostseriousdisadvantageisthatallbutoneofthecodesthatsatisfythiscriterionmustsacrificesomeproportionoftheirdatarate(seeAlamouti'scode).
Moreover,thereexistquasi-orthogonalSTBCsthatachievehigherdataratesatthecostofinter-symbolinterference(ISI).Thus,theirerror-rateperformanceislowerboundedbytheoneoforthogonalrate1STBCs,thatprovideISIfreetransmissionsduetoorthogonality.
HigherorderSTBCs
Tarokhetal.discoveredasetofSTBCsthatareparticularlystraightforward,andcoinedthescheme'sname.Theyalsoprovedthatnocodeformorethan2transmitantennascouldachievefull-rate.Theircodeshavesincebeenimprovedupon(bothbytheoriginalauthorsandbymanyothers).Nevertheless,theyserveasclearexamplesofwhytheratecannotreach1,andwhatotherproblemsmustbesolvedtoproduce'good'STBCs.Theyalsodemonstratedthesimple,lineardecodingschemethatgoeswiththeircodesunderperfectchannelstateinformationassumption.
4transmitantennas
Twostraightforwardcodesfor4transmitantennasare:
and
Thesecodesachieverate-1/2andrate-3/4respectively,asfortheir3-antennacounterparts.C4,3/4exhibitsthesameunevenpowerproblemsasC3,3/4.AnimprovedversionofC4,3/4is
whichhasequalpowerfromallantennasinalltime-slots.
Decoding
OneparticularlyattractivefeatureoforthogonalSTBCsisthatmaximumlikelihooddecodingcanbeachievedatthereceiverwithonlylinearprocessing.Inordertoconsideradecodingmethod,amodelofthewirelesscommunicationssystemisneeded.
Attimet,thesignal
receivedatantennajis:
whereαijisthepathgainfromtransmitantennaitoreceiveantennaj,
isthesignaltransmittedbytransmitantennaiand
isasampleofadditivewhiteGaussiannoise(AWGN).
Themaximum-likelihooddetectionruleistoformthedecisionvariables
whereδk(i)isthesignofsiinthekthrowofthecodingmatrix,εk(p)=qdenotesthatspis(uptoasigndifference),the(k,q)elementofthecodingmatrix,fori=1,2...nTandthendecideonconstellationsymbolsithatsatisfies
with
theconstellationalphabet.Despiteitsappearance,thisisasimple,lineardecodingschemethatprovidesmaximaldiversity.
References
[1]GerardJ.FoschiniandMichael.J.Gans(January1998).“Onlimitsofwirelesscommunicationsinafadingenvironmentwhenusingmultipleantennas”.WirelessPersonalCommunications6(3):
311–335.
[2]GerardJ.Foschini(autumn1996).“Layeredspace-timearchitectureforwirelesscommunicationsinafadingenvironmentwhenusingmulti-elementantennas”.BellLabsTechnicalJournal1
(2):
41–59.
[3]I.EmreTelatar(November1999).“Capacityofmulti-antennaEuropeanTransactionsonTelecommunications,10(6):
585–595.
[4]VahidTarokh,NambiSeshadri,andA.R.Calderbank(March1998)."Space–timecodesforhighdataratewirelesscommunication:
Performanceanalysisandcodeconstruction".IEEETransactionsonInformationTheory44
(2):
744–765.
译文
基于MIMO-OFDM系统的正交空时分组码
本文介绍了移动通信中的空时码,针对多天线系统提出了空时分组码的正交设计理论,可以采用高效的调制技术(QAM,PSK),由多天线同时发射。
接收端采用最大似然译码可以获得最大的分集增益。
并因空时码有很高的频谱利用率,从而使空时码在未来移动通信及无线局域岗中得到广泛的应用。
介绍
Alamouti于1998年提出了一种发射端采用两根天线的空时分组码方案,该方案能够实现最大分集增益和全发射速率,在接收端使用了简单的最大似然译码。
为了将空时分组码推广到多个天线,VahidTarokh等基于满分集提出了正交空时分组码。
由于正交空时分组编码发射矩阵各行之间的正交性,可以获得满分集增益,但是当发射天线数大于2时,利用复正交设计得到的正交空时分组编码不能达到最大传输速率。
为此,H.Jafarkhan等和Tirkkonen等分别提出了两种基于全速率的准正交空时分组编码,即Jafarkhani码和TBH码。
JiaHou等在Jafarkhani码和TBH码的基础上,讨论了变形Jafarkhani码和变形TBH码,并提出了2种新的准正交编码。
在既定的情况下,在特定的数据流传输编码在blocks块,间隔,将分布在天线和跨越时空。
虽然是必要的,它有多个发射天线,这是没有必要有多个接收天线,虽然这样做改进效能。
这个过程接收不同的数据备份,是众所周知的最大似然译码,直到1998年Foschini研究论文。
空时编码通常用矩阵来表示。
在矩阵中,每一行代表一个时间段,而每一列代表每一根天线的传输。
正交
由于最初的对空时编码做出的研究,并介绍了这样的正交。
这意味着,例如既定设计向量任何两个柱代表掠正交编码矩阵。
这是简单的结果,线性,最佳解码的接收机。
最严重的不利因素是所有之一,同时满足这一标准法典,必须牺牲一些比例的数据传输速率。
此外,存在着在利率,以达到更高的数据传输干扰的成本(ISI)。
因此,他们的误码率是空时编码的界定标准之一,正交率提供免费传授由于正交码。
高阶空时编码方法
Tarokhetal等在1998年10月发现了一组空时编码。
这是特意直截了当的以创造了这个方案的创始人名字为名。
他们也证明了不能超过2个发射天线可以达到的目标。
他们的代码。
一直以来的改进。
然而,作为明确的例子,为什么不能到达率1,其他什么必须解决的问题有如何用空时码接收更好的信号。
他们也体现了简单的,直线解码是伴随着他们的编码方案,在完美的信道状态信息。
4个发射天线
两个直截了当的代码为4发射天线是:
以及
.
这些编码实现-1/2比特和-3/4比特的空时编码,
从所有具有相同能力的天线可知。
译码
一个特别吸引人的特征的正交STBC就是这个了最大似然解码,可以较好地实现在接收者对而已线性加工。
为了考虑解码方法,无线通信系统的模型是必需的。
在时间t上的信号,
天线接收到的是:
是路径获得传送天线吗接收天线
是信号通过传送天线i和
有一份添加剂白色高斯噪声检测规则的就是要形成的决策变量。
满足对于准正交空时分组编码而言,由于发射矩阵的各行不是完全正交的,因此在接收端进行最大似然译码时需对信号进行联合检测,这就使得其译码算法较之正交空时分组编码要复杂一些。
由最大似然准则,其解码过程即求
其中,
是映射后的符号。
虽然从表面上看,这是一个简单的直线解码方案,提供最大的似然性。
参考文献
[1]GerardJ.FoschiniandMichael.J.Gans(January1998)."Onlimitsofwirelesscommunicationsinafadingenvironmentwhenusingmultipleantennas".WirelessPersonalCommunications6(3):
311–335.
[2]GerardJ.Foschini(autumn1996)."Layeredspace-timearchitectureforwirelesscommunicationsinafadingenvironmentwhenusingmulti-elementantennas".BellLabsTechnicalJournal1
(2):
41–59.
[3]I.EmreTelatar(November1999)."Capacityofmulti-antennagaussianchannels".EuropeanTransactionsonTelecommunications,10(6):
585–595.
[4]VahidTarokh,NambiSeshadri,andA.R.Calderbank(March1998)."Space–timecodesforhighdataratewirelesscommunication:
Performanceanalysisandcodeconstruction".IEEETransactionsonInformationTheory44
(2):
744–765.
外文资料
(二)
Unit-RateComplexOrthogonalSpace-TimeBlockCodeConcatenatedWithTurboCoding
Space-TimeBlock(STB)codehasbeenaneffectivetransmitdiversitytechniqueforcombatingfadingduetoitsorthogonaldesign,simpledecodingandhighdiversitygins.Inthispaper,aunit-ratecomplexorthogonalSTBcodeformultipleantennasinTimeDivisionDuplex(TDD)modeisproposed.Meanwhile,TurboCoding(TC)isemployedtoimprovetheperformanceofproposedSTBcodefurtherbyutilizingitsgoodabilitytocombatthebursterroroffadingchannel.Comparedwithfull-diversitymultipleantennasSTBcodes,theproposedcodecanimplementunitrateandpartialdiversity;andithaymuchsmallercomputationalcomplexityunderthesamesystemthroughput.Moreover,theapplicationofTCcaneffectivelymakeupfortheperformancelossduetopartialdiversity.SimulationresultsshowthatontheconditionofsamesystemthroughputandconcatenationofTC,theproposedcodehaslowerBitErrorRate(BER)thanthosefull-diversitycodes.
Ⅰ.Introduction
Recently,transmitdiversityhasbeenstudiedextensivelyasamethodofcombatingdetrimentaleffectsinwirelessfadingchannelsduetoitsrelativesimplicityofimplementandfeasibilityofhavingmultipleantennasattheBaseStation(BS).Asimpletransmitterdiversityschemeusingtw0transmitantennasisproposedbyAlamouti.Anextensiontomorethantwotransmitantennasispresented,whereitisshownthattheAlamoutischemeisaspecialcaseofSpace-TimeBlock(STB)code.