通信英语训练试题综合一

PAGEPAGE1（unit1、7、ⅠⅡⅢⅣⅤ一、单项选择题（110分Furthermore,weshallprovethataminimumtheoreticalsamplingfrequencyoforder6.8kHzisrequiredavoicechanneltherange300Hzto3.4kHz. B.toconvey,C.conveying, D.convey,toIfweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbysimplythepresenceorabsenceofthepulse.obtain, B.beobtained,C.obtained, D.obtaining,Eachvoicechannelhasaseparatecoder,theunitconvertssampledamplitudevaluestoasetofpulses;anddecoder,theunitperformsthereverseoperation.who, B.when,C.where, D.that,Theproblemiseasily ebyaframeformat,whereatthestartofeachframeauniquesequenceofpulsesiscedthestartoftheframe. B.specifying,soastoC.specified, D.specify,Ifsomebodyelsehadsomethinginterestingontheircomputer,itwasasimplematteracopy.stored,to B.tostore,C.storing, D.store,Themostcommonlynetworkserviceiselectronicmail(E-mail),orsimplyasmail.Mailpermitsnetworkuserstextualmessagestoeachother.use, B.touse,C.used,to D.using,Todaythousandsofnetworksandmillionsofcomputers theareconnected B.connectedC.to D.Thesimplestway afileonanotherhostistocopyitacrossthenetworktoyourlocalhost.FTPcandothis. B.toC. D.Oneofmanyreasonsfor acellular ephonesystemanditinmanycitiesistheconventional ephonesystem.develop, B.todevelop,toC.develo, D.developed,LSItechnologyandmassproductioncontributetoreducedcostinthefuturean efamilyshouldbeableaephonewhich, B.that,when, D.sothat,to二、英译汉短语（115分aminimumtheoreticalsamplingavoicechanneloccupyingtherange300Hzto3.48-digitspersampletheattenuationintroducedbytransmissionremotenetworkfacilitiestextualthenetworkedhypertextfrequencyspectrumpropagationpathcomplicatedfeaturesandtheallocatedfrequencymultipath15theshapeofthetransmitted三、汉译英短语（115分1、同步字 .2、二进制传 3、数字通 4、地 5、互联 6、公众电信 7、网络资 8、频 9、服务 10、蜂窝交换 12、服务性 13、超文本协 14、用户界 15、文本信 四、阅读理解（220分，根据文章内容判断（√（X）Digitaltransmissionprovidesapowerfulmethodfor environments.Noisecanbeintroducedintotransmissionpathindifferentways:perhapsviaanearbylightningstrike,thesparkingofacarignitionsystem,orthethermallow-levelnoisewithinthecommunicationequipmentitself.Itistherelationshipofthetruesignaltothenoisesignal,knownasthesignal-to-noiseratio,whichisofthemostinteresttothecommunicationengineer.Basically,ifthesignalisverylargecomparedtothenoiselevel,thenaperfectmessagecantakece;however,thisisnotalwaysthecase.Forexample,thesignalreceivedfromasalite,locatedinfarouterspace,isveryweakandisatalevelonlyslightlyabovethatofthenoise.Alternativeexamplesmaybefoundwithinterrestrialsystemswhere,althoughthemessagesignalisstrong,soisthenoisepower.Ifweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbeobtainedbysimplydetectingthepresenceorabsenceofthepulse.Bycomparison,mostotherformsoftransmissionsystemsconveythemessageinformationusingtheshape,orlevelofthetransmittedsignal;parametersthataremosteasilyaffectedbythenoiseandattenuationintroducedbythetransmissionpath.Consequentlythereisaninherentadvantagefor ingnoisyenvironmentsbychoosingdigitaltransmission.Ifthetruesignalisverylargecomparedtothenoiselevel,thentheinformationwithhigherqualitycanbeobtained.()Ifweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbeobtainedbydetectingtheshapeofthetransmittedsignalorbycalculatingtheparametersofthetransmittedsignal.()Itisthesignal-to-noiseratiowhichisofthemostinteresttothecommunicationengineer.()Digitaltransmissionprovidesthesignal-to-noiseratio,whichisaveryimportantparameter,for ingnoisyenvironments.()Thesignalgottenfromasaliteisgenerallyveryweak.(Theshapeofthetransmittedsignalaremosteasilyaffectedbythenoiseandattenuationintroducedbythecodec.()Sofarwehaveassumedthateachvoicechannelhasaseparatecoder,theunitthatconvertssampledamplitudevaluestoasetofpulses;anddecoder,theunitthatperformsthereverseoperation.Thisneednotbeso,andsystemsareinoperationwhereasinglecodec(i.e.,coderanditsassociateddecoder)issharedbetween24,30,oreven120separatechannels.Ahigh-speedelectronicswitchisusedtopresenttheoginformationsignalofeachchannel,takeninturn,tothecodec.Thecodecisthenarrangedtosequentiallysampletheamplitudevalue,andcodethisvalueintothe8-digitsequence.Thustheoutputtothecodecmaybeseenasasequenceof8pulsesrelatingtochannel1,thenchannel2,andsoon.Thisunitiscalledatimedivisionmultiplexer(TDM).Themultiplexingprinciplethatisusedisknownaswordinterleaving.Sincethewords,or8-digitsequences,areinterleavedintime.Atthereceiveterminalademultiplexerisarrangedtoseparatethe8-digitsequencesintotheappropriatechannels.Thereadermayask,howdoesthedemultiplexetknowwhichgroupof8-digitsrelatestochannel1,2,andsoon?Clearlythisisimportant!Theproblemiseasily ebyspecifyingaframe,whereatthestartofeachframeauniquesequenceofpulsescalledtheframecode,orsynchronizationword,iscedsoastoidentifythestartoftheframe.Acircuitofthedemultiplexerisarrangedtodetectthesynchronizationword,andtherebyitknowsthatthenextgroupof8-digitscorrespondstochannel1.Thesynchronizationwordreoccursonceagainafterthelastchannelhasbeenreceived.Atthereceiveterminalthereverseoperationtothemultiplexingisneededtoseparatethe8-digitsequencesintotheappropriatechannels.( Thedemultiplexerknowswhichgroupof8-digitsrelatestochannel1assoonasitfindsthesynchronizationword.( Thetimedivisionmultiplexerissocalledsincethereisaspecialwordcalledsynchronizationword.( Thegroupof8-digitsfollowingthesynchronizationwordrelateschannel1. 五、英译汉短文（1040分Ifweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbeobtainedbysimplydetectingthepresenceorabsenceofthepulse.Bycomparison,mostotherformsoftransmissionsystemsconveythemessageinformationusingtheshape,orlevelofthetransmittedsignal;parametersthataremosteasilyaffectedbythenoiseandattenuationintroducedbythetransmissionpath.Consequentlythereisaninherentadvantagefor ingnoisyenvironmentsbychoosingdigitaltransmission.Basically,ifthesignalisverylargecomparedtothenoiselevel,thenaperfectmessagecantakece;however,thisisnotalwaysthecase.Forexample,thesignalreceivedfromasalite,locatedinfarouterspace,isveryweekandisatalevelonlyslightlyabovethatofthenoise.Alternativeexamplesmaybefoundwithinterrestrialsystemswhere,althoughthemessagesignalisstrong,s