通信英语教学课件汇总完整版电子教案全书课件.ppt

通信英语1、通信专业基础知识2、基础英语知识专业英语学习的要素：通信英语学习的三个要点：1、常见语法现象2、构词方法3、翻译方法和技巧重要提示：1、网上作业提交2、综合练习3、课后练习ThePrincipleofPCM专业背景介绍专业背景介绍PCMisdependentonthreeseparateoperations,sampling,quantizing,andcoding.dependentadj.依靠，依赖依靠，依赖onseparateadj.不同的不同的operationn.操作，运算，手术操作，运算，手术samplev.取样取样quantizev.量化量化codev.编码编码Manydifferentschemesforperformingthesethreefunctionshaveevolvedduringrecentyears,andweshalldescribethemainones.schemen.方案，计划方案，计划performv.执行，完成执行，完成functionn.功能功能evolvev.发展，演化发展，演化recentadj.近来近来describev.描述描述Inthesedescriptionsweshallseehowaspeechchanneloftelephonequalitymaybeconveyedasaseriesofamplitudevalues,eachvaluebeingrepresented,thatis,coded,asasequenceof8binarydigits.descriptionn.描述描述channeln.信道，话路信道，话路conveyv.转化，传达转化，传达amplituden.幅度representv.表示，代表sequencen.序列binaryadj.二进制的Furthermore,weshallprovethataminimumtheoreticalsamplingfrequencyoforder6.8kilohertz(kHz)isrequiredtoconveyavoicechanneloccupyingtherange300Hzto3.4kHz.provev.证明minimumn.最小值frequencyn.频率ordern.数量级，命令occupyv.占据，占用rangen.范围Practicalequipments,however,normallyuseasamplingrateof8kHz,andif8-digitspersamplevalueareused,thevoicechannelbecomesrepresentedbyastreamofpulseswitharepetitionrateof64kHz.equipmentn.设备设备normallyadv.通常地通常地ratesn.速率速率streamn.流流repetitionn.重复重复Reexaminationofoursimpleexampleshowsusthatthespeechsignalofmaximumfrequency3.4kHzhasbeenrepresentedbyasignaloffrequency64kHz.reexaminationn.再审查，再看再审查，再看showv.展示，表演展示，表演maximumn.最大值最大值However,ifonly4-digitspersamplevaluehadbeenused,thequalityoftransmissionwoulddrop,andtherepetitionrateofthepulseswouldbereducedto32kHz.qualityn.质量质量transmissionn.传输传输dropv.下降下降reducev.减少减少Thusthequalityoftransmissionisdependentonthepulserepetitionrate,andfordigitalcommunicationsystemsthesetwovariablesmaybeinterchangedmostefficiently.variablen.变量变量interchangev.相互转换相互转换efficientlyadv.有效的有效的Digitaltransmissionprovidesapowerfulmethodforovercomingnoisyenvironments.powerfuladj.有力的，有力的，methodn.方法方法overcomev.克服克服environmentn.环境环境Noisecanbeintroducedintotransmissionpathinmanydifferentways:perhapsviaanearbylightningstrike,thesparkingofacarignitionsystem,orthethermallow-levelnoisewithinthecommunicationequipmentitself.Introducev.引入，介绍引入，介绍Lightningn.闪电闪电striken.打，打击sparkv.闪烁，打火球ignitionn.点火thermaladj.热的leveln.电平Itistherelationshipofthetruesignaltothenoisesignal,knownasthesignal-to-noiseratio,whichisofthemostinteresttothecommunicationengineer.relationshipn.关系关系Basically,ifthesignalisverylargecomparedtothenoiselevel,thenaperfectmessagecantakeplace;however,thisisnotalwaysthecase.basicallyadv.基本上的基本上的compareto比作比作perfectadj.完美的完美的messagen.消息，信息消息，信息takeplace发生发生Forexample,thesignalreceivedfromasatellite,locatedinfarouterspace,isveryweakandisatalevelonlyslightlyabovethatofthenoise.satelliten.卫星卫星locatev.位于位于slightlyadv.稍微稍微noisen.噪声噪声Alternativeexamplesmaybefoundwithinterrestrialsystemswhere,althoughthemessagesignalisstrong,soisthenoisepower.alternativeadj.替代的，迂回的替代的，迂回的terrestrialadj.地面的地面的Ifweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbeobtainedbysimplydetectingthepresenceorabsenceofthepulse.considerv.考虑考虑completeadj.完整的完整的obtainv.获得获得detectv.检测检测presencen.出席，到场出席，到场absencen.缺席，不在缺席，不在Bycomparison,mostotherformsoftransmissionsystemsconveythemessageinformationusingtheshape,orlevelofthetransmittedsignal;parametersthataremosteasilyaffectedbythenoiseandattenuationintroducedbythetransmissionpath.bycomparison相比之下相比之下shapen.波形，形状波形，形状parametern.参数参数affectv.影响影响attenuationv.衰减衰减pathn.路径路径Consequentlythereisaninherentadvantageforovercomingnoisyenvironmentsbychoosingdigitaltransmission.consequentlyadv.因而因而inherentadj.固有的，本质的固有的，本质的advantagen.优势优势choosev.选择选择Sofarinthisdiscussionwehaveassumedthateachvoicechannelhasaseparatecoder,theunitthatconvertssampledamplitudevaluestoasetofpulses;anddecoder,theunitthatperformsthereverseoperation.sofar至此，迄今为止至此，迄今为止assumev.假定假定Thisneednotbeso,andsystemsareinoperationwhereasinglecodec(i.e.,coderanditsassociateddecoder)issharedbetween24,30,oreven120separatechannels.inoperation运转着，生效运转着，生效codec编解码器编解码器associatev.使发生联系，使联合使发生联系，使联合sharev.共用，分享共用，分享Ahigh-speedelectronicswitchisusedtopresenttheanaloginformationsignalofeachchannel,takeninturn,tothecodec.switchn.开关开关presentv.引见引见,给给,上演上演,提出提出,呈现呈现informationn.信息信息takeinturn轮流轮流Thecodecisthenarrangedtosequentiallysampletheamplitudevalue,andcodethisvalueintothe8-digitsequence.arrangev.安排安排sequentiallyadv.顺序的顺序的samplev.取样取样Thustheoutputtothecodecmaybeseenasasequenceof8pulsesrelatingtochannel1,thenchannel2,andsoon.output输出输出relateto涉及，对应涉及，对应Thisunitiscalledatimedivisionmultiplexer(TDM),andisillustratedinFig.1-2.divisionn.分开分开multiplexern.复用器复用器illustratev.描述，说明描述，说明Themultiplexingprinciplethatisusedisknownaswordinterleaving,sincethewords,or8-digitsequences,areinterleavedintime.beknownas被称作，被认为被称作，被认为interleavev.复用，间插复用，间插Thereadermayask,howdoesthedemultiplexerknowwhichgroupof8-digitsrelatestochannel1,2,andsoon?Clearlythisisimportant!demultiplexern.分路器分路器Atthereceiveterminalademultiplexerisarrangedtoseparatethe8-digitseq。