通信英语教学课件电子教案全书课件.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-digitsequencesintotheappropriatechannels.terminaln.终端终端separatev.分开分开appropriateadj.适当的适当的Theproblemiseasilyovercomebyspecifyingaframeformat,whereatthestartofeachframeauniquesequenceofpulsescalledtheframecode,orsynchronizationword,isplacedsoastoidentifythestartoftheframe.specifyv.指定，详细说明指定，详细说明framen.帧帧uniqueadj.唯一的，独特的唯一的，独特的synchronizationn.同步字同步字identifyv.标识标识Acircuitofthedemultiplexerisarrangedtodetectthesynchronizationword,andtherebyitknowsthatthenextgroupof8-digitscorrespondstochannel1.Thesynchronizationwordreoccursonceagainafterthelastchannelhasbeenreceived.reoccurv.再发生，再出现再发生，再出现翻译要点：1、被动句翻译2、词类转换3、定语从句翻译4、宾语从句翻译5、状语从句翻译UNIT2AsynchronousSerialDatatransmission背景介绍ByfarthemostpopularserialinterfacebetweenacomputeranditsCRTterminalistheasynchronousserialinterface.byfar用来修饰比较级和最高级interfacen.接口CRT阴极射线管asynchronous异步的Thisinterfaceissocalledbecausethetransmitteddataandthereceiveddataarenotsynchronizedoveranyextendedperiodandthereforenospecialmeansofsynchronizingtheclocksatthetransmitterandreceiverisnecessary.synchronizev.使同步extendv.扩展，延伸specialadj.特殊的meansn.手段，方法clockn.时钟Infact,theasynchronousserialdatalinkisaveryoldformofdatatransmissionsystemandhasitsoriginintheeraofteleprinter.infact事实上事实上linkn.链路，线路，中继线链路，线路，中继线originn.起源，开始起源，开始teleprintern.电传打字机电传打字机Serialdatatransmissionsystemshavebeenaroundforalongtimeandarefoundinthetelephone(humanspeech),Morsecode,semaphore,andeventhesmokesignalsonceusedbynativeAmericans.semaphoren.旗语smokesignal烽火Thefundamentalproblemencounteredbyallserialdatatransmissionsystemsishowtosplittheincomingdatastreamintoindividualunits(i.e.,bits)andhowtogrouptheseunitsintocharacters.fundamentaladj.基本的，根本的encounterv.遇到splitv.分开incomingadj.输入的，进来的individualn.个别的，单个的unitn.单元，部件charactern.字符Forexample,inMorsecodethedotsanddashesofacharacterareseparatedbyaninter-symbolspace,whiletheindividualcharactersareseparatedbyaninter-characterspace,whichisthreetimesthedurationofaninter-symbolspace.dotn.点dashn.短划线separatev.分开inter-symbol符号间inter-character字符间spacen.空间，间隔durationn.持续时间Firstweexaminehowthedatastreamisdividedintoindividualbitsandthebitsgroupedintocharactersinanasynchronousserialdatalink.Thekeytotheoperationofthistypeoflinkisbothsimpleandingenious.Fig.2-1givestheformatofdatatransmittedoversuchalink.examinev.检查，查看streamn.流dividev.分开keyn.要点，关键ingeniousadj.精巧的Anasynchronousserialdatalinkissaidtobecharacteroriented,asinformationistransmittedintheformofgroupsofbitscalledcharacters.orientedv.面向，朝向Thesecharactersareinvariableunitscomprising7or8bitsof“information”plus2to4controlbitsandfrequentlycorrespondtoASCII-encodedcharacters.invariableadj.固定不变的comprising包括frequently通常的correspondto对应ASCIIInitially,whennoinformationisbeingtransmitted,thelineisinanidlestate.Traditionally,theidlestateisreferredtoasthemarklevel.Byconventionthiscorrespondstoalogical1level.initiallyadv.开始的开始的idleadj.空闲的，懒散的空闲的，懒散的traditionallyadv.传统的传统的referto称作称作markn.传号传号convention宗教会议宗教会议by习惯习惯logicaladj.逻辑的逻辑的Whenthetransmitterwishestosenddata,itfirstplacesthelineinaspacelevel(i.e.,thecomplementofamark)foroneelementperiod.ThiselementiscalledthestartbitandhasadurationofTseconds.wishv.希望placev.设置spacen.空号elementn.元素，单元Thetransmitterthensendsthecharacter,1bitatatime,byplacingeachsuccessivebitonthelineforadurationofTseconds,untilallbitshavebeentransmitted.successiveadj.连续的Thenasingleparitybitiscalculatedbythetransmitterandsentafterthedatabits.Finally,thetransmittersendsastopbitatamarklevel(i.e.,thesamelevelastheidlestate)foroneortwobitperiods.Nowthetransmittermaysendanothercharacterwheneveritwishes.parityn.奇偶校验，奇偶校验，calculaten.计算计算Atthereceivingendofanasynchronousserialdatalink,thereceivercontinuallymonitorsthelinelookingforastartbit.Oncethestartbithasbeendetected,thereceiverwaitsuntiltheendofthestartbitandthensamplesthenextNbitsattheircenters,usingaclockgeneratedlocallybythereceiver.continuallyadv.连续的monitorv.监测lookfor寻找detectv.检测endn.结束generatev.产生Aseachincomingbitissampled,itisusedtoconstructanewcharacter.Whenthereceivedcharacterhasbeenassembled,itsparityiscalculatedandcomparedwiththereceivedparitybitfollowingthecharacter.Iftheyarenotequal,aparityerrorflagissettoindicateatransmissionerror.constructv.建设，组成assemblev.装配，汇齐comparev.比较equaladj.相等的errorn.差错flagn.标志indicatev.指示Themostcriticalaspectofthesystemisthereceivertiming.Thefallingedgeofthestartbittriggersthereceiverslocalclock,whichsampleseachincomingbitatitsnominalcenter.criticaladj.紧要的，关键的aspectn.方面timingn.定时edgen.边，沿triggerv.触发，启动nominaladj.标称的，名义的SupposethereceiverclockwaitsT/2secondsfromthefallingedgeofthestartbitandsamplestheincomingdataeveryTsecondsthereafteruntilthestopbithasbeensampled.Fig.2-2showsthissituation.Asthereceiversclockisnotsynchronizedwiththetransmitterclock,thesamplingisnotexact.supposev.假设situationn.情况exactadj.精确的Themostobviousdisadvantageofasynchronousdatatransmissionistheneedforastart,parity,andstopbitforeachtransmittedcharacter.If7bitcharactersareused,theoverallefficiencyisonly70%.obviousadj.明显的disadvantagen.缺点overalladj.整个的efficiencyn.效率Alessobviousdisadvantageisduetothecharacter-orientednatureofthedatalink.WheneverthedatalinkconnectsaCRTterminaltoacomputer,fewproblemsarise,astheterminalisitselfcharacteroriented.However,ifthedatalinkisbeingusedto,say,dumpbinarydatatoamagnetictape,problemsarise.dueto由于naturen.特性dumpv.倾倒，转储magneticadj.磁的UNIT4Internet背景介绍TheInternetisagiantnetworkofcomputerslocatedallovertheworldthatcommunicatewitheachother.gianta.巨大的locatev.位于TheInternetisaninternationalcollectionofcomputernetworksthatallunderstandastandardsystemofaddressesandcommands,connectedtogetherthroughbackbonesystems.collectionn.收集，聚集standardn.标准addressn.地址commandn.命令backbonen.骨干Itwasstartedin1969,whentheU.S.DepartmentofDefenseestablishedanationwidenetworktoconnectahandfulofuniversitiesandcontractors.DepartmentofDefense国防部establishv.建立nationwidea.全国性的handfuln.少数，少量universityn.大学contractorn.订阅人，承包人Theoriginalideawastoincreasecomputingcapacitythatcouldbesharedbyusersinmanylocationsandtofindoutwhatitwouldtakeforcomputernetworkstosurviveanuclearwarorotherdisasterbyprovidingmultiplepathbetweenusers.Originala.最初的，开始的Increasev.增加Computev.计算Capacityn.容量Sharev.分享，共用Findout找出，发现，查明survivev.幸免于，幸存，生还nucleara.原子能的，核的disastern.灾难，天灾multiplea.许多的pathn.路径PeopleontheARPNETquicklydiscoveredthattheycouldexchangemessagesandconductelectronic“conferences”withdistantcolleaguesforpurposesthathadnothingtodowiththemilitaryindustrialcomplex.exchangev.交换conductv.进行，从事conferencen.会议militarya.军事的complexa.复杂的;n.综合企业Ifsomebodyelsehadsomethinginterestingstoredonhisorhercomputer,itwasasimplemattertoobtainacopy.obtainv.获得copyn.拷贝Overtheyears,additionalnetworksjoinedwhichaddedaccesstomoreandmorecomputers.Thefirstinternationalconnection,toNorwayandEngland,wereaddedin1973.TodaythousandsofnetworksandmillionsofcomputersareconnectedtotheInternet.ItisgrowingsoquicklythatnobodycansayexactlyhowmanyusersOntheNet5.TheInternetisthelargestrepositoryofinformationwhichcanprovideveryverylargenetworkresources.Thenetworkresourcescanbedividedintonetworkfacilitiesresourcesandnetworkinformationresources.Thenetworkfacilitiesresourcesprovideustheabilityofremotecomputationandcommunication.Thenetworkinformationresourcesprovideusallkindsofinformationservices,suchasscience,education,business,history,haw,art,andentertainment,etc.repositoryn.仓库，资料丰富的地方resourcen.资源facilityn.设备，工具entertainmentn.娱乐，乐趣ThegoalofyouruseoftheInternetisexchangingmessagesorobtaininginformation.WhatyouneedtoknowisthatyoucanexchangemessagewithothercomputersontheInternetanduseyourcomputerasaremoteterminalondistantcomputers6.Buttheinternaldetailsofthelinkarelessimportant,aslongasitworks.Ifyouconnectcomputerstogetheronanetwork,eachcomputermusthaveauniqueaddress,whichcouldbeeitherawordoranumber.Forexample,theaddressofSamscomputercouldbeSam,oranumber.TheInternetisahugeinterconnectedsystem,butitusesjustahandfulofmethodtomovedataaround.UntiltherecentexplosionofpublicinterestintheInternet,thevastmajorityofthecomputersontheNetusetheUnixoperatingsystem.Asaresult,thestandardUnixcommandsforcertainInternetserviceshaveenteredtheonlinecommunityslanguagesasbothnounsandverbstodescribetheservicesthemselves.SomeoftheservicesthattheInternetcanprovideare:Mail,Remoteuseofanothercomputer(Telnet),FileTransfer(FTP),News,andLiveconversation.explosionn.爆炸，扩张，激增majorityn.多数，大多数Themostcommonlyusednetworkserviceiselectronicmail(E-mail),orsimplyasmail.Mailpermitsnetworkuserstosendtextualmessagestoeachother.Computersandnetworkshandledeliveringthemail,sothat7communicatingmailusersdonothavetohandledetailsofdelivery,anddonothavetobepresentatthesametimeorplace.Thesimplestwaytoaccessafileonanotherhostistocopyitacrossthenetworktoyourlocalhost.FTPcandothis.Presently,auserwithanaccountonanyInternetmachinecanestablishaliveconnectiontoanyothermachineontheNetfromtheterminalinhisownofficeorlaboratory.It8isonlynecessarytousetheUnixcommandthatsetsuparemoteterminalconnection(Telnet),followedbytheaddressofthedistantmachine.BeforeyoucanusetheInternet,youmustchooseawaytomovedatabetweentheInternetandyourPC.Thislinkmaybeahigh-speeddatacommunicationcircuits,alocalareanetwork(LAN),atelephonelineoraradiochannel.Mostlikely,youwilluseaModemattachedtoyourtelephonelinetotalktotheInternet.Naturally,thequalityofyourInternetconnectionandservice,likemanyotherthingsinlife9,isdictatedbytheamountofmoneyyouarewillingtospend.choosev.选择，挑选attachv.缚，系，附加modemn.调制解调器dictatev.命令，支配Althoughalltheseservicescanwellsatisfytheneedsoftheusersforinformationexchange,adefiniterequirementisneededfortheusers.Notonlyshouldtheusersknowwheretheresourceslocate,butalsoheshouldknowsomeoperatingcommandsconcerned10.Toeasethesearchingburdenoftheusers,recentlysomeconvenientsearchingtoolsappear,suchasGopher,WWWandNetscape.satisfyvt.满足，使满意definitea.明确的，确切的，肯定的requirementn.需要，要求WorldWideWeb(WWW)isanetworkedhypertextprotocolanduserinterface.ItprovidesaccesstomultipleservicesanddocumentslikeGopherdoesbutismoreambitiousinitsmethod.AjumptootherInternetservicecanbetriggeredbyamouseclickona“hot-linked”word,image,oriconontheWebpage.hypertextn.超级文本interfacen.接口，界面am