通信与电子信息专业英语 课件 Unit 7 Principles of Communications

Unit7PrinciplesofCommunications7.1ElectricalCommunicationSystems

7.2ModulationandMultiplexing

7.3DigitalCommunicationTechniques7.1ElectricalCommunicationSystemsWordsandExpressionsBackgroundsTextWordsandExpressionscommunication

n.通信；交流；传递；交通联系communicationengineeringcommunicationtechnology3Dhologram三维全息影像telepathy

心灵感应；传心术WordsandExpressionstransmission

n.(电子信号、信息或广播电视节目的)传输，发送transmit/receive v.发送/接收transmitter/receiver n.发送方/接收方intelligence n.情报；智力；才智；智慧AI:ArtificialIntelligence 人工智能5WordsandExpressionsinformation n.信息；消息；情报；资料；资讯ManymeansforthetransmissionofinformationhavebeenuseddownthroughtheagesrangingfromtheuseofsunlightreflectedfrommirrorsbytheRomanstoourmoderneraofelectricalcommunicationsthatbeganwiththeinventionofthetelegraphinthe1800s.从罗马人使用镜子反射阳光到19世纪电报发明开启的现代电气通信时代，人类使用了许多方法来传输信息。6WordsandExpressionsuncertainty

n.不确定性certainty确定uncertaintyprinciple

测不准原理，不确定性原理perturbation n.扰动；干扰；微扰；小变异(physics)asecondaryinfluenceonasystemthatcausesittodeviateslightlyvelocityperturbation 速度波动thermalperturbation 温度扰动7WordsandExpressionsprobabilistic adj.基于概率的；或然的Noisehasbeenanever-presentproblemsincetheearlydaysofelectricalcommunication,butitwasnotuntilthe1940sthatprobabilisticsystemsanalysisprocedureswereusedtoanalyzeandoptimizecommunicationsystemsoperatinginitspresence.自电气通信早期以来，噪声是一个始终存在的问题，但直到1940年代，概率系统分析方法才被用来分析和优化在噪声存在的情况下的通信系统。8WordsandExpressionsdeterioration n.恶化，变坏；退化mechanicaldeterioration

机械损伤environmentaldeterioration

环境恶化Inthehigh-speedlonghaulopticalnetworks,theproblemofthesignaldeteriorationduringthetransmissionmustbesolved.在长距离超高速光通信网络中，光信号在传输过程中的恶化是一个必须解决的问题。9WordsandExpressionstransducer n.传感器；换能器；变换器Sensorsfundamentallydetectthephysicalvariationsthatoccurinthesurrounding,transformitintoameaningfulquantity,andinducethecorrespondingelectricalsignals.Otherwise,thetransducerisaninstrumentthatconvertstheenergyfromoneformtoanotherformwhenactuates.10WordsandExpressionschannel n.信道；频道；电视台；波段Achannelhasacertaincapacityfortransmittinginformation,oftenmeasuredbyitsbandwidthinHzoritsdatarateinbitspersecond.additivenoise 加性噪声Multiplicativenoisemodelsareoftenusedinsteadofadditivenoisemodelsincasesinwhichthenoisevariancedependsonthestate.11WordsandExpressionsdistortion

n.失真；变形；扭曲powerlinecoronadischarge 电力线电晕放电Thephenomenonofvioletglow,hissingnoiseandproductionofozonegasinanoverheadtransmissionlineisknownascorona.12WordsandExpressionsremotesensing

遥感；遥测Remotesensingisthescienceofobtainingthephysicalpropertiesofanareawithoutbeingthere.sonar:soundnavigationandranging

声呐；声波定位仪techniquefordetectinganddeterminingthedistanceanddirectionofunderwaterobjectsbyacousticmeans.13WordsandExpressions14sample

n.样品；样本vt.采样；抽样quantizev.量化transmissionmedium 传输介质intercomsystem 内部通信系统；对讲机系统WordsandExpressionsmodulate v.调制；调节；调整；控制carrier n.载波amplitude n.(声音、无线电波等的)振幅phase n.相位；阶段；时期15WordsandExpressionsattribute

n.属性；特征；性质；定语Modulationisthesystematicvariationofsomeattributeofthecarrier,suchasamplitude,phase,orfrequency,inaccordancewithafunctionofthemessagesignal.radiation

n.辐射；放射线；辐射的热(或能量等)filter n.滤波器；筛选(过滤)程序 v.滤波；(用程序)筛选16WordsandExpressionsantenna n.天线alsocalledAerial,componentofradio,television,andradarsystemsthatdirectsincomingandoutgoingradiowaves.17WordsandExpressionspropagate v.传播degradation n.毁坏，恶化(过程)demodulate v.解调；检波MODEM:Modulator-DemodulatorCODEC:Coder-DecoderMUX/DEMUX:MultiplexerandDemultiplexer18WordsandExpressionsSX:simplex

单工FDX:full-duplex 全双工HDX:half-duplex 半双工19Background20AnalogCommunication,/course/analog-communication/TextOutlineBriefHistoryCommunicationSystemComponentsInputTransducerTransmitterChannelReceiverOutputTransducer21BriefHistoryAsystemisacombinationofcircuitsand/ordevicesthatisassembledtoaccomplishadesiredtask,suchasthetransmissionofintelligencefromonepointtoanother.Acharacteristicofelectricalcommunicationsystemsisthepresenceofuncertainty.22BriefHistoryThisuncertaintyisdueinparttotheinevitablepresenceinanysystemofunwantedsignalperturbations,broadlyreferredtoasnoise,andinparttotheunpredictablenatureofinformationitself.这种不确定性，部分是由于在任何系统中不可避免地存在不必要的信号扰动，广义上称为噪声，部分是由于信息本身的不可预测性。23BriefHistoryItisaninterestingfactthatthefirstelectricalcommunicationsystem,thetelegraph,wasdigital…Thesubsequentinventionofthetelephone38yearsafterthetelegraph…24BriefHistoryOnemayrightlyask,inviewofthishistory,whydigitalformatsarealmostcompletedominantintoday’sworld?SignalintegrityMediaintegrationFlexibleinteractionEditing25CommunicationSystemComponentsRegardlessoftheparticularapplicationandconfiguration,allinformationtransmissionsystemsinvariablyinvolvethreemajorsubsystems—atransmitter,thechannel,andareceiver.无论具体应用和配置如何，所有信息传输系统都必须包含三个主要子系统：发射方、信道和接收方。26InputTransducerRegardlessoftheirexactform,however,messagesmaybecategorizedasanalogordigital.Theformermaybemodeledasfunctionsofacontinuous-timevariable(forexample,pressure,temperature,speech,music),whereasthelatterconsistofdiscretesymbols(forexample,writtentextorasampled/quantizedanalogsignalsuchasspeech).27InputTransducer28Almostinvariably,themessageproducedbyasourcemustbeconvertedbyatransducertoaformsuitablefortheparticulartypeofcommunicationsystememployed.几乎无一例外，信源产生的消息必须由传感器转换为适合所采用的特定类型通信系统传输的形式。TransmitterThepurposeofthetransmitteristocouplethemessagetothechannel.Inadditiontomodulation,otherprimaryfunctionsperformedbythetransmitterarefiltering,amplification,andcouplingthemodulatedsignaltothechannel(forexample,throughanantennaorotherappropriatedevice).29TransmitterThereareseveralreasonsforusingacarrierandmodulatingit:foreaseofradiationtoreducenoiseandinterferenceforchannelassignmentformultiplexingtoovercomeequipmentlimitations30ChannelThechannelcanhavemanydifferentforms…However,allchannelshaveonethingincommon:thesignalundergoesdegradationfromtransmittertoreceiver.信道可以有许多不同的形式...然而，所有信道都有一个共同点：信号从发射机到接收机都会恶化。31ChannelThisdegradationoftenresultsfromnoiseandotherundesiredsignalsorinterference,

butalsomayincludeotherdistortioneffectsaswell,suchasfadingsignallevels,multipletransmissionpaths,andfiltering.这种信号恶化通常由噪声和其他不希望的信号或干扰引起，但也可能包括其它失真效应，如衰落信号电平、多路径传输和滤波。32ReceiverThereceiver’sfunctionistoextractthedesiredmessagefromthereceivedsignalatthechanneloutputandtoconvertittoaformsuitablefortheoutputtransducer.接收器的功能是从信道输出的接收信号中提取所需的消息，并将其转换为适合输出传感器的形式。33ReceiverOftenitisdesiredthatthereceiveroutputbeascaled,possiblydelayed,versionofthemessagesignalatthemodulatorinput,althoughinsomecasesamoregeneralfunctionoftheinputmessageisdesired.尽管在某些情况下，希望接收机输出的信号与调制器的输入信号具有更一般的函数关系，一般情况还是希望接收机输出的信号是调制器输入信号经过缩放、可能时延的版本。34OutputTransducerThisdeviceconvertstheelectricsignalatitsinputintotheformdesiredbythesystemuser.Perhapsthemostcommonoutputtransducerisaloudspeakerorearphone.输出传感器把输入的电信号转换为系统用户所需的形式。也许最常见的输出传感器就是扬声器或耳机。357.2ModulationandMultiplexingWordsandExpressionsBackgroundsText36WordsandExpressionsbaseband n.(无线)基带；基频Basebandreferstotheoriginalfrequencyrangeofatransmissionsignalbeforeitisconverted,ormodulated,toadifferentfrequencyrange.passbandsignal（带通信号）:passbandsignalreferstomodulatedorfilteredsignalwhichultimatelygetsconvertedbacktobasebandsignal.WordsandExpressionsLAN:LocalAreaNetwork 局域网WordsandExpressionscoaxialcable

同轴电缆twisted-pair

双绞线WordsandExpressionsbroadband n.宽带ahigh-capacitytransmissiontechniqueusingawiderangeoffrequencies,whichenablesalargenumberofmessagestobecommunicatedsimultaneously.oscillator n.振荡器oscillatorcircuit 振荡电路crystaloscillator

晶体振荡器VCO:Voltage-ControlledOscillator

压控振荡器40WordsandExpressionsAM:AmplitudeModulation 调幅FM:FrequencyModulation 调频PM:PhaseModulation 调相FSK:Frequency-ShiftKeying 频移键控PSK:Phase-ShiftKeying 相移键控41WordsandExpressionsdetector n.检波器；探测器envelopedetector 包络检波器synchronousdetector

同步检波器FDM:FrequencyDivisionMultiplexing

频分复用TDM:TimeDivisionMultiplexing

时分复用CDM:CodeDivisionMultiplexing

码分复用WDM:WavelengthDivisionMultiplexing 波分复用42Background43ModulationinCommunicationSystemforRF,/course/digital-analog-introduction-to-modulation-in-communication-systems/TextOutlineIntroductionBasebandTransmissionBroadbandTransmissionMultiplexing44IntroductionModulationmakestheinformationsignalmorecompatiblewiththemedium,andmultiplexingallowsmorethanonesignaltobetransmittedconcurrentlyoverasinglemedium.调制技术使得信息信号与传输介质更兼容，而复用技术则允许在单个传输介质上同时传输多路信号。45BasebandTransmissionBeforeitcanbetransmitted,theinformationorintelligencemustbeconvertedtoanelectronicsignalcompatiblewiththemedium.Regardlessofwhethertheoriginalinformationorintelligencesignalsareanalogordigital,theyareallreferredtoasbasebandsignals.46BasebandTransmission47Puttingtheoriginalvoice,video,ordigitalsignalsdirectlyintothemediumisreferredtoasbasebandtransmission.Inmanyinstances,basebandsignalsareincompatiblewiththemedium.Thehigher-frequencycarriersradiateintospacemoreefficientlythanthebasebandsignalsthemselves.Suchwirelesssignalsconsistofbothelectricandmagneticfields.BasebandTransmission48Theseelectromagneticsignals,whichareabletotravelthroughspaceforlongdistances,arealsoreferredtoasradio-frequency(RF)waves,orjustradiowaves.这些能够在空间中长距离传播的电磁信号也称为射频（RF）波，或仅称为无线电波。BroadbandTransmission49Modulationistheprocessofhavingabasebandvoice,video,ordigitalsignalmodifyanother,higher-frequencysignal,thecarrier.BroadbandTransmission50Theinformationorintelligencetobesentissaidtobeimpresseduponthecarrier.Thecarrierisusuallyasinewavegeneratedbyanoscillator.Themodulatedcarrierisamplifiedandsenttotheantennafortransmission.Thisprocessiscalledbroadbandtransmission.BroadbandTransmission51Thethreewaystomakethebasebandsignalchangethecarriersinewavearetovaryitsamplitude,varyitsfrequency,orvaryitsphaseangle.BroadbandTransmission52Amplitudemodulation&Frequencymodulation.

BroadbandTransmission53Transmittingbinarydatainanalogform:Frequency-shiftKeying&Phase-shiftKeyingBroadbandTransmission54Atthereceiver,thecarrierwiththeintelligencesignalisamplifiedandthendemodulatedtoextracttheoriginalbasebandsignal.Anothernameforthedemodulationprocessisdetection.Multiplexing55Theuseofmodulationalsopermitsanothertechnique,knownasmultiplexing,tobeused.Multiplexingistheprocessofallowingtwoormoresignalstosharethesamemediumorchannel:Multiplexing56Atthereceiver,thecompositesignalisrecoveredatthedemodulator,thensenttoademultiplexerwheretheindividualbasebandsignalsareregenerated.Multiplexing57Therearethreebasictypesofmultiplexing:frequencydivision,timedivision,andcodedivision.Inopticalnetworking,wavelengthdivisionmultiplexing(WDM)isequivalenttofrequency-divisionmultiplexingforopticalsignal.58Iftheinformationsignalsaresampledfastenough,sufficientdetailsaretransmittedthatatthereceivingendthesignalcanbereconstructedwithgreataccuracy.如果信息信号的采样速度足够快，则会传输足够的细节，以便在接收端可以非常精确地重建信号。Multiplexing7.3DigitalCommunicationTechniquesWordsandExpressionsBackgroundsText59WordsandExpressionsdigitize vt.(使数据)数字化encode vt.编码；把…译成电码(或密码)Translatingananalogsignaltoadigitalsignaliscalledanalog-to-digital(A/D)conversion,digitizingasignal,orencoding.将模拟信号转换为数字信号称为模数（A/D）转换、信号数字化或编码。decoder n.(电子信号)解码器，译码器CODEC(=decodercoder)

信号编解码器WordsandExpressionsreciprocal

n.倒数Akeyfactorinthesamplingprocessisthefrequencyofsamplingf,whichisthereciprocalofthesamplingintervaltshowninFigure7.8.采样过程中的一个关键因素是采样频率f，它是图7.8所示采样间隔t的倒数。quantizingerror

量化误差WordsandExpressionsPCM:Pulse-CodeModulation 脉冲编码调制WordsandExpressionsredundancy n.冗余；多余Informationredundancy

信息冗余CyclicRedundancyCheck

(CRC) 循环冗余校验Dataredundancy 数据冗余RedundantArrayofIndependentDisks(RAID)独立冗余磁盘阵列63WordsandExpressionsdatacompression 数据压缩Datacompression,alsocalledcompaction,theprocessofreducingtheamountofdataneededforthestorageortransmissionofagivenpieceofinformation,typicallybytheuseofencodingtechniques.数据压缩通常通过使用编码技术来减少存储或传输给定信息所需的数据量。sourceencoder 信源编码器channelencoder 信道编码器64WordsandExpressionsfidelity

n.保真度；精确性HiFi:HighFidelity 高保真colourfidelity

色彩保真度elaborate v.详尽阐述；详细描述opticalfiber

光纤65Background66PrinciplesofDigitalCommunications,/courses/6-450-principles-of-digital-communications-i-fall-2006/video_galleries/video-lectures/TextOutlineIntroductionDataConversionA/DConversionD/AConversionElementsofaDigitalCommunicationSystem67IntroductionToday,thankstotheavailabilityoffast,low-costanalog-to-digital(A/D)anddigital-to-analog(D/A)convertersandhigh-speeddigitalsignalprocessors,mostelectroniccommunicationsare

digital.如今，由于快速、低成本的模数（A/D）和数模（D/A）转换器以及高速数字信号处理器的出现，大多数电子通信都是数字通信。68DataConversionAmodernA/Dconverterisusuallyasingle-chipICthattakesananalogsignalandgeneratesaparallelorserialbinaryoutput.TheinputtoaD/Aconvertermaybeaserialorparallelbinarynumber,andtheoutputisaproportionalanalogvoltagelevel.69DataConversionAlthoughtheoreticallythehighestfrequencycomponentcanbeadequatelyrepresentedbyasamplingrateoftwicethehighestfrequency,inpracticethesamplingrateismuchhigherthantheNyquistminimum,typically2.5to3timesmore.虽然理论上采用两倍于最高频率分量的采样率，得到的样本信号足以代表原始信号，但在实践中，采样率远高于奈奎斯特最小值，通常是其2.5到3倍。70DataConversion71ThephysicalnatureofanA/Dconverterissuchthatitdividesavoltagerangeintodiscreteincrements,eachofwhichisthenrepresentedbyabinarynumber.Theanalogvoltagemeasuredduringthesamplingprocessisassignedtotheincrementofvoltageclosesttoit.A/D转换器的物理特性是，它将电压范围划分为离散增量，然后每个增量用二进制数表示。采样过程中测量的模拟电压值用最接近它的离散电压增量来表示。DataConversion72Notethatalthoughthereare16levels,thereareonly15increments.Thenumberoflevelsis2Nandthenumberofincrementsis2N-1,whereNisthenumberofbits.DataConversion73Butwhathappensiftheanaloginputis11.7V,asshowninFigure7.9?TheA/Dconverterproducesthebinarynumber1011,whosedecimalequivalentis11.Asyoucansee,thereissomeerrorassociatedwiththeconversionprocess.Thisisreferredtoasquantizingerrorwhichcanbereduced,ofcourse,bysimplydividingtheanalogvoltagerangeintoalargernumberofsmallervoltageincrements.DataConversion74Becausetheinputbinarynumbersrepresentspecificvoltagelevels,theoutputoftheD/Aconverterhasastairstepcharacteristic.由于输入二进制数表示特定的电平，因此D/A转换器的输出具有阶梯特性。DataConversion75However,thestairstepscanbefilteredoutbypassingtheD/Aconverteroutputthroughalow-passfilterwithanappropriatecutofffrequency.然而，D/A转换器输出信号的阶梯形状，可以通过具有适当截止频率的低通滤波器来滤除。ElementsofaDigitalCommunicationSystem76ElementsofaDigitalCommunicationSystem77Thesourceoutputmaybeeitherananalogsignal,suchasanaudioorvideosignal,oradigitalsignal,suchastheoutputofacomputer,thatisdiscreteintimeandhasafinitenumberofoutputcharacters.信源输出可以是模拟信号，例如音频或视频信号，也可以是数字信号，如计算机的输出，其在时间上是离散的，并且具有有限数量的输出字符。ElementsofaDigitalCommunicationSystem78Ideally,weshouldliketorepresentthesourceoutput(message)byasfewbinarydigitsaspossible.Inotherwords,weseekanefficientrepresentationofthesourceoutputthatresultsinlittleornoredundancy.Theprocessofefficientlyconvertingtheoutputofeitherananalogordigitalsourceintoasequenceofbinarydigitsiscalledsourceencodingordatacompression.ElementsofaDigitalCommunicationSystem79Thepurposeofthechannelencoderistointroduce,inacontrolledmanner,someredundancyinthebinaryinformationsequencethatcanbeusedatthereceivertoovercometheeffectsofnoiseandinterferenceencounteredinthetransmissionofthesignalthroughthechannel.信道编码器的目的是以可控的方式在二进制信息序列中引入一些冗余，这些冗余可用于在接收机处消除信号在信道传输中受到的噪声和干扰的影响。ElementsofaDigitalCommunicationSystem80Binarymodulation:Thedigitalmodulatormaysimplymapthebinarydigit0intoawaveforms0(t)andthebinarydigit1intoawaveforms1(t).M-arymodulation(M>2):Alternatively,themodulatormaytransmitbcodedinformationbitsatatimebyusingM=2bdistinctwaveformssi(t),i=0,1...M−1,onewaveformforeachofthe2b

possibleb-bitsequences.81Whateverthephysicalmediumusedfortransmissionoftheinformation,theessentialfeatureisthatthetransmittedsignaliscorruptedinarandommannerbyavarietyofpossiblemechanisms,suchasadditivethermalnoisegeneratedbyelectronicdevices;man-madenoise,e.g.,automobileignitionnoise;andatmosphericnoise,e.g.,electricallightningdischargesduringthunderstorms.ElementsofaDigitalCommunicationSystem82Atthereceivingendofadigitalcommunicationsystem,thedigitaldemodulatorprocessesthechannel-corruptedtransmittedwaveformandreducesthewaveformstoasequenceofnumbersthatrepresentestimatesofthetransmitteddatasymbols(binaryorM-ary).在数字通信系统的接收端，数字解调器处理被信道损坏的传输波形，将这些波形简化为传输数据符号（二元或M元）估计值的数字序列。ElementsofaDigitalCommunicationSystem83Thissequenceofnumbersispassedtothechanneldecoder,whichattemptstoreconstructtheoriginalinformationsequencefromknowledgeofthecodeusedbythechannelencoderandtheredundancycontainedinthereceiveddata.该数字序列被传送到信道解码器，信道解码器试图根据信道编码器使用的代码和接收数据中包含的冗余信息来重构原始信息序列。ElementsofaDigitalCommunicationSystem84Ingeneral,theprobabilityoferrorisafunctionofthecodecharacteristics,thetypesofwaveformsusedtotransmittheinformationovert