通信工程专业外语-unit13原文与翻译

精选优质文档-----倾情为你奉上精选优质文档-----倾情为你奉上专心---专注---专业专心---专注---专业精选优质文档-----倾情为你奉上专心---专注---专业Unit13ComparisonbetweenGSMandCDMAGSM与CDMA之比较UsingCDMA/FDDtechnology,subscribersofCDMAcellularmobilecommunicationsystemcantransmittheirinformationsimultaneouslythroughthesamechannel.Ontheotherhand,theGSMsystemadoptsTDMA/FDDmethodtotransmitanddistinguishinformationfromdifferentGSMmobilestations.Inaddition,infavorofQCELParithmetic,RAKEreceiver,powercontrolandsoftswitchingetc.,CDMAshowsmoreadvantagesinitssystemperformancethantheGSM,suchasgreateranti-interferencecapability,biggersystemcapacity,highersuccessfulconnectionratio,feweroff-linechances,lowprobabilityofintercept(LPI),andsoon.使用码分多址/频分双工技术，用户的蜂窝移动通信系统的传输信息的同时，通过同样的渠道。另一方面，该系统采用时分多址/频分双工传输的方法和识别信息从不同的移动台。此外，有利于中国电信集团广州研发中心算术，耙式接收器，功率控制和软开关等，显示出更多的优势在码分多址系统性能比，如更高的抗干扰能力，更大的系统容量，连接成功率较高，离线的机会少，低截获概率（低截获概率），等。1,PowerControlandRAKEReceiver功率控制和瑞克接收机WhendifferentsubscriberssendtheirinformationtothesameBS(basestation),differentsignalpowercausedbydifferenttransmittingdistanceswillconsequentiallycauseinterferencewitheachother,especiallyforthoseMSs(mobilestation)beingfarawayfromBSwillbeseriouslydisturbedbecauseoftheiralmostsubmergedsignalsbysignalsoftheclose-to-BSMSs.[2]p110Inordertosolvethisproblemandkeephighsystemperformance,powercontroltechniqueisintroducedinCDMAcommunicationsystem,whichcaneffectivelyovercomethiscross-disturbance.AsoneofthecoretechniquesinCDMAcellularmobilecommunicationsystem,powercontrolcanmakethesignalpowerfromallsubscriberstotheBSequivalentthroughadjustingthetransmittingpowerfromeachsubscriber.为解决这一问题，保持较高的系统性能，功率控制技术介绍了码分多址通信系统，它可以有效地克服这cross-disturbance。作为一个核心技术在蜂窝移动通信系统的功率控制，可以使信号功率从所有用户的学士学位相当于通过调整发射功率，从每个用户。Powercontrolcanbenotonlydividedtoopen-loopcontrolandclosed-loopcontrol,butalsotoforward(down)powercontrolandbackward(up)powercontrol.Foropen-loopcontrolmethod,subscriberadjustsemittingpoweraccordingtothemeasuredframeerrorprobability,whilefortheclosed-looppowercontrol,basestationmeasuresthesignal-to-noiseratioofreceivedsignalsandthenadjustthetransmittingpowerofcorrespondingMS.功率控制不仅可以分为开环控制和闭环控制，而且还提出了（下）功率控制和反向功率控制（上）。开环控制方法，用户调整发射功率根据测量帧错误概率，同时为闭环功率控制，基站测量接收信号的信噪比，然后调整发射功率相应的女士ThebackwardpowercontrolinCDMAsystemcanbedividedintotwokindsofcontroltechnique,theopen-loopbackwardpowercontrolonlyusedbymobilestation,andtheclosed-loopbackwardpowercontrolthatcanbeadoptedbybothbasestationandmobilestation.Ontheotherhand,theforwardpowercontrolisjustusedtoreducethedisturbancefromsmalladjacentdistricts.反向功率控制系统可分为开环控制技术，反向功率控制用的移动站，以及闭环反向功率控制，可以通过基站和移动站。另一方面，正向功率控制是用来降低干扰小附近的地区。RAKEReceptionTechnique(瑞克接收技术)Fadinganddistortionareinevitableforsignalstransmittedinmobilecommunicationchannelbecauseoftheunidealcharacteristicsofchannel,andthenmakebadinfluenceonsystemperformance.变形是不可避免的衰落和信号传输的移动通信信道因为不理想的信道特性，进而会影响系统的性能。ThebasictheoryofRAKEreceptiontechniqueis:bymeansofcollectingalltransmittedsignalsfrommulti-pathandunitingthem,thereceivedsignalpowercanobtainaneffectiveenhancement,whichcanimprovetheoutputSNRandsystemperformance.[3]p110Three,fourRAKEreceiversarerespectivelysetineachMS,BSinCDMAsysteminordertoreceivethearrivingbranchsignalofthesameoriginalfromdifferenttransmittingroutes,andthencombinethemtogetanincrescentoutputSNRaftertheirrespectivelyindependentdemodulation.Thus,infavorofRAKEreceptiontechnique,thedisadvantageousfactorthatsignaltransmittedinmulti-pathbecauseanadvantageousfactorinCDMAcellularmobilecommunicationsystem.三，四的耙式接收器分别设置于每一毫秒，在码分多址系统，以便接收到信号相同的原始分支从不同的传播途径，并结合他们得到一个增大的输出信噪比后分别独立解调。因此，有利于瑞克接收方法，发送信号的不利因素，因为一个有利因素在多径码分多址蜂窝移动通信系统。2BetterPerformanceofCDMA性能更好的码分多址GreaterAnti-interferenceCapability更大的抗干扰能力Becauseofspreadspectrummodulation,bandwidthofuser’ssignalisextremelybroadenedbytheassigneduniquepseudo-randomsequence,thusthemodulatedbroadbandsignalownsspectralpropertiesclosetoGaussianwhitenoise.Receivingthiskindofspreadspectrumsignal,alltheCDMAreceiverstrytodemodulateitusingPNsequencecreatedlocally,butonlyonereceiverwiththesamelocalPNsequenceasthatinthereceivedsignalcanconvertthebroadbandnoise-likesignalintonarrowbandusefulsignal,whileotherreceiverisstilltheinsignificantbroadbandnoiseexcepttherelativedemodulatorwiththeuniquelocalPNsequence.由于扩频调制，带宽用户的信号是非常扩大的分配独特的伪随机序列，从而调制的宽带信号拥有光谱性能接近高斯白噪声。接受这种扩频信号，所有的码分多址接收机尝试使用伪随机序列解调本地创建，但只有一个接收相同的本地伪码序列，在接收信号可以转换成宽带类噪声信号为窄带有用信号，而其他接收器仍然是微不足道的宽带噪声，除了相关解调器与当地独特的伪随机序列。Inaddition,asfarasthenarrowbandmeaninglesssignaladditivetothereceivedsignalbytherelativereceiverwiththesameuniquepseudo-randomsequence,itismodulatedintobroadbandsignalwithextremelylessenedpowerspectraldensity.Thus,therelativereceivercanfilterthebroadbandsignalfromotherusersandmajorityofthemeaninglesssignaloutofthefilterbandwidthjustthroughanarrowbandfilter.Therefore,reservationinwithinthereceiveronlyconsistsofthenarrowbandusefulsignalandlittlemeaninglesssignalwithinthefilterbandwidth.Asaconsequentresult,theoutputsignal-to-noiseratioisimprovedlargely,thatwillnecessarilyleadstogreatersystemanti-interferencecapability.此外，至于窄带毫无意义的信号添加剂的接收信号的相对接收相同的独特的伪随机序列，它是调制成宽带信号的功率谱密度非常减少。因此，相对接收器可以过滤宽带信号从其他用户和广大的毫无意义的信号进行滤波器的带宽是通过窄带滤波器。因此，保留在接收由窄带有用信号和小无意义的信号在滤波器的带宽。作为一个必然结果，输出信噪比有较大的提高，这必然会导致更大的系统的抗干扰能力。ItcanbeprovedthatthemorehighvalueofBn/Bb,themoregreatsystemanti-interferencecapability.由于扩频调制，带宽用户的信号是非常扩大的分配独特的伪随机序列，从而调制可以证明更高价值的Bn/Bb，更大的系统的抗干扰能力。BiggerSystemCapacityandHigherSuccessfulAccessRatio更大的系统容量和更高的接入成功率UnliketheTDMAmulti-accessmodeinGSMmobilecommunicationsystem,signalofeachCDMAsubscriberisdistinguishedbytheassigneduniquePNsequencebasedontheCDMAtechnology.Thus,eachsignalofCDMAsubscribercanbetransmittedsynchronouslyoccupyingtheentiresub-channelbandwidthdividedfromtheFDDmethod.Soundertheequalfrequencyresourcecondition,inotherword,forthesamechannelbandwidth,capacityofCDMAsystemis4~5timeslargerthanthatofGSMsystem.不同的是时分多址接入模式在移动通信系统中，信号的每个用户的特点是独特的伪随机序列的分配基于码分多址技术。因此，每一个信号，用户可同步传输信道带宽占整个分从故障诊断方法。所以在同等频率资源条件，换句话说，在同一信道带宽，码分多址系统容量为4~5倍以上的系统。Inthenatureofthings,acommunicationsystemwithbigcapacitymusthavehighsuccessfulaccessratio.在事物的性质，通信系统容量大，必须具备较高的接入成功率。Inaddition,usingCELP(CodeExcitedLinearPredictive)arithmeticforvoicecode,audiosignalinCDMAsystemcanbetransmittedwithvariablespeed,withthemaximumCELPcodedaudiosignaltransmittingvelocityis9.6kbit/swhilethesubscriberistalking,andtheminimumvelocityof1.2kbit/sfortheconversationpause.ThistechniquecalledVoiceActivationcanreducethebackgrounddisturbanceamongsubscriberscommunicatingononechannelatthesametime,andenhancesthesystemcapacity.ForGSMsystem,thisVoiceActivationtechniquecannotbeusedbecauseofthesignaltransmittingdelayatconversationpause.此外，利用线性预测（码激励线性预测）算法的语音编码，音频信号在码分多址系统可以传播速度可变，以最大线性预测编码的音频信号传输速率为9.6比特每秒而用户说话，和最低速度的1.2比特每秒的谈话暂停。这种技术称为语音激活能降低背景干扰用户间的通信在一个频道在同一时间，并提高了系统容量。全球移动通讯系统，该语音激活技术无法使用，由于信号传输延迟谈话停顿。BetterVoiceQuality更好的声音质量UsingadvancedCELP(CodeExcitedlinearPredictive)arithmeticforitsdigitalaudiosignalcode,and3RAKEreceiversinahandsettoreceivesignalsfromdifferentdirectionssimultaneously,itismadeextremelyabundantanddimensionalforaudiosignalspectrumfromCDMAhandset.Furthermore,vocoderbasedontheCELParithmeticinCDMAsystemcanadjustitstransmittingvelocityandchoosecorrespondingsendingpowerlevelautomaticallytoreducethedisturbanceofnoise.Thus,evenunderthecircumstancewithloudnoise,wecanmakeconversationofgoodqualitywithoutanycacophony.采用先进的线性预测（码激励线性预测）算法的数字音频信号的代码，在手机和3接收机接收来自不同方向的信号的同时，它是极其丰富和三维音频信号频谱从手机。此外，声码器的线性预测算法在码分多址系统可以调整其传输速度和选择相应的发送功率电平自动减少噪声的干扰。因此，即使在情况下的声音，我们可以把会话质量好无杂音。LowerProbablyofIntercept(LPI)下可能拦截（低截获概率）Itisnecessaryforeavesdroppingsomebody'sconversionthatthetransmittedconversioninformationmustbecapturedandthendecoded.ForCDMAsystem,signalwithuser'sinformationmustbespreadspectrummodulatedbeforesenttothecommonchannelwithextremelyspreadspectrumandverylowpowerspectraldensity.ThusitistoodifficulttodetectthiskindofCDMAsignalforthelistener-inbecauseitspowerspectraldensityisevenlowerthanambientnoise,andit'salmostimpossibleforhimtodistinguishthesignalfrombackgroundnoise.这是必要的窃听别人的转换，传输转换信息必须捕获和解码。用于码分多址系统的信号，用户的信息必须发送扩频调制前的共同渠道极扩频和非常低的功率谱密度。因此，这是很难检测到这种信号的收听者因为其功率谱密度甚至低于环境噪声，它几乎不可能为他区分信号从背景噪音。Moreover,evenifthesignaliscaptured,whatthelistener-incangetonlybroadbandnoiseofinsignificancefromhisdemodulatorbecauseofhisinaccuratelocalpseudo-randomsequence.TheprobabilityofrightPNsequencepatternnecessaryforspreadspectrumdemodulationisoneofmorethanonethousandbillion!Whatalowprobabilityforlistener-intoeavesdropother'sconversationthroughCDMAcellularmobilecommunicationsystem!此外，即使信号捕获的听众，仅能获得宽带噪声微不足道从解调器因为他的不准确的本地伪随机序列。概率的正确的序列模式所必需的扩频解调是超过一千个亿！什么是低概率的听众偷听别人的谈话通过蜂窝移动通信系统！FewerOff-linechances离线的机会较少Becauseofthesoft-switchingtechnique,whichmeans“connect-before-break”,it’sovercomeforCDMAthatthefrequentoccurrenceofoff-time.由于软开关技术，即“connect-before-break”，它克服了码分多址，频繁发生的时间。Inmobilecommunicationsystem,BSistheguaranteeforconversation.WhensubscribersduringconversationmovingclosetoedgeoftheBS’demesne,theBSshouldmaintainthecommunicationthroughitsactiveswitching,otherwisetheprocesswillbeinterrupted.Duringswitchingperiod,BS’sdominionshouldshiftfrom“demesneofthelocalBS(suchasA)”to“demesneofAanditsneighboringBS(B)”to“demesneofB”,andsignalfromthemovingmobilestationwillautomaticallyswitchtoarelativelyidleneighboringBS.Thus,onlywhenitisapprovedthatthemovingMShasmovedtothe“demesneofB”,cantheconnectionbetweenthemovingMSanditsoriginalBS(A)beswitchedoff.SoitisnoteasyforaCDMAconversationtobeinterruptedbyoff-line.在移动通信系统，基站是保证谈话。当用户在会话移动接近边缘的学士学位的私有化，如要保持通信通过其主动开关，否则程序中断。在切换期间，英国的主权应该从“私有的地方本科（如）”到“私有和邻近基站（乙）”到“私有”，和信号从移动台移动会自动