通信英语课程教案.docx
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通信英语课程教案.docx
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通信英语课程教案
通信英语
讲课人张筱华
第一部分关于课程的几点说明
一、课程的基本内容
本课程选用教材为“通信英语”(第五版),张筱华、石方文编。
二、考试的范围和要求
鉴于本书的内容较多,考试的基本范围仅选为“通信英语”的第一、九课。
考试方式为闭卷,笔试。
考题的形式与综合练习题(即课后练习题)基本一致。
这些练习题其实都来自课文。
换句话说,只要同学们认真阅读了这几篇课文,就能顺利地通过期末考试。
综合练习题中共有五类题目,这里可分述如下:
1、专业词组的英译汉(期末考试采用)
2、专业词组的汉译英(期末考试采用)
3、选择填空(四中选一:
测试语法)
4、选择填空(四中选一:
测试对课文的理解)
5、课文段落翻译(英译汉)(期末考试采用)
考试将采用1、2、5三种题目,而阶段作业将采用3、4类题目。
显然,认真阅读这几课并准备好课后练习,是一个好办法。
三、教学的形式和安排
1、导学:
已挂在网络上,供大家下载进行学习。
在导学中介绍了考试范围及要求;介绍了教学的方式及安排;讲解了最主要的语法现象和课文。
2、利用互联网进行辅导,共两次。
四、学习成绩的认定
本课程的最终成绩由以下部分组成:
1、阶段作业成绩占30%。
2、期末考试成绩占70%。
第二部分
《通信英语》中主要的语法现象
一.动名词
作用相当于名词,它在句子中可做主语、宾语或介词宾语。
例如:
1.Readingisagoodhabit.
动名词在句子中做主语。
2.Ienjoyworkingwithyou.
动名词在句子中做宾语.
3.Iaminterestedinreading.
动名词在句子中做介词宾语。
动名词的作用虽然相当于名词,但它仍然具有一些动词的特征。
例如,它可以有自己的宾语和状语。
例如:
4.Iaminterestedincarefullyreadingbooks.
二.现在分词
1)现在分词一般作形容词用,可修饰动作的发出者,有主动的意义。
可译成“……的……”,此时多作定语。
例如:
1.ThesmilinggirlisWangling.
2.Thisisanamusingstory.
在更多情况下,我们用现在分词短语作定语,在作用上和一个定语从句差不多。
例如:
3.Thegirlstandingbythewindowtalkedtoherfriend.
2)现在分词(或分词短语)还可以作状语,用来表示方式、目的、条件、结果和背景等等;有时表示主语在作一个动作的同时还进行的另一动作,此时称之为伴随状态。
例如:
1.EveryeveningtheysitinsofawatchingTV.
现在分词起伴随作用。
可以比较:
EveryeveningtheysitinsofaandwatchTV.
2.IreadtheEnglishbook,usingmydictionary.
现在分词表示条件或背景。
三、过去分词
过去分词(短语)一般作形容词用,可修饰动作的对象,有被动的意义。
可译成“被……的……”或“由……的……”,此时多作定语。
例如:
Thetreesplantedbymehavegrownup.
现在分词和过去分词在意思上相去甚远,在翻译时应特别注意,例如:
thecalledperson:
被叫人
thecallingperson:
主叫人
四、动词不定式
在《通信英语》中,动词不定式大量地用来做状语。
动词不定式在句首或句末常常用来表示目的,可译成“为了……”“以便……”,可见这时候起状语作用。
例如:
1.Todoagoodjob,weusegoodtools.
2.Weusegoodtoolstodoagoodjob.
由于英语中常用被动语态,所以上面的例子可表示为:
3.Goodtoolsareusedtodoagoodjob.
注意此例中的下划线部分,这类句型在“计算机网络专业英语”中大量出现。
类似的句型还有:
……isusedtodo………
……isneededtodo……
……isrequiredtodo……
……isarrangedtodo……
第三部分课文讲解
UNIT1
ThePrincipleofPCM
PCMisdependentonthreeseparateoperations,sampling,quantizing,andcoding.Manydifferentschemesforperformingthesethreefunctionshaveevolvedduringrecentyears,andweshalldescribethemainones.Inthesedescriptionsweshallseehowaspeechchanneloftelephonequalitymaybeconveyedasaseriesofamplitudevalues,eachvaluebeingrepresented,thatis,coded,asasequenceof8binarydigits.Furthermore,weshallprovethataminimumtheoreticalsamplingfrequencyoforder6.8kilohertz(kHz)isrequiredtoconveyavoicechanneloccupyingtherange300Hzto3.4kHz.Practicalequipments,however,normallyuseasamplingrateof8kHz,andif8-digitspersamplevalueareused,thevoicechannelbecomesrepresentedbyastreamofpulseswitharepetitionrateof64kHz.Fig.1-1illustratesthesampling,quantizing,andcodingprocesses.
Reexaminationofoursimpleexampleshowsusthatthespeechsignalofmaximumfrequency3.4kHzhasbeenrepresentedbyasignaloffrequency64kHz.However,ifonly4-digitspersamplevaluehadbeenused,thequalityoftransmissionwoulddrop,andtherepetitionrateofthepulseswouldbereducedto32kHz.Thusthequalityoftransmissionisdependentonthepulserepetitionrate,andfordigitalcommunicationsystemsthesetwovariablesmaybeinterchangedmostefficiently.
Digitaltransmissionprovidesapowerfulmethodforovercomingnoisyenvironments.Noisecanbeintroducedintotransmissionpathinmanydifferentways;perhapsviaanearbylightningstrike,thesparkingofacarignitionsystem,orthethermallow-levelnoisewithinthecommunicationequipmentitself.Itistherelationshipofthetruesignaltothenoisesignal,knownasthesignal-to-noiseratio,whichisofthemostinteresttothecommunicationengineer.Basically,ifthesignalisverylargecomparedtothenoiselevel,thenaperfectmessagecantakeplace;however,thisisnotalwaysthecase.Forexample,thesignalreceivedfromasatellite,locatedinfarouterspace,isveryweakandisatalevelonlyslightlyabovethatofthenoise.Alternativeexamplesmaybefoundwithinterrestrialsystemswhere,althoughthemessagesignalisstrong,soisthenoisepower.
Ifweconsiderbinarytransmission,thecompleteinformationaboutaparticularmessagewillalwaysbeobtainedbysimplydetectingthepresenceorabsenceofthepulse.Bycomparison,mostotherformsoftransmissionsystemsconveythemessageinformationusingtheshape,orlevelofthetransmittedsignal;parametersthataremosteasilyaffectedbythenoiseandattenuationintroducedbythetransmissionpath.Consequentlythereisaninherentadvantageforovercomingnoisyenvironmentsbychoosingdigitaltransmission.
Sofarinthisdiscussionwehaveassumedthateachvoicechannelhasaseparatecoder,theunitthatconvertssampledamplitudevaluestoasetofpulses;anddecoder,theunitthatperformsthereverseoperation.Thisneednotbeso,andsystemsareinoperationwhereasinglecodec(i.e.,coderanditsassociateddecoder)issharedbetween24,30,oreven120separatechannels.Ahigh-speedelectronicswitchisusedtopresenttheanaloginformationsignalofeachchannel,takeninturn,tothecodec.Thecodecisthenarrangedtosequentiallysampletheamplitudevalue,andcodethisvalueintothe8-digitsequence.Thustheoutputtothecodecmaybeseenasasequenceof8pulsesrelatingtochannel1,thenchannel2,andsoon.Thisunitiscalledatimedivisionmultiplexer(TDM),andisillustratedinFig.1-2.Themultiplexingprinciplethatisusedisknownaswordinterleaving.Sincethewords,or8-digitsequences,areinterleavedintime.
Atthereceiveterminalademultiplexerisarrangedtoseparatethe8-digitsequencesintotheappropriatechannels.Thereadermayask,howdoesthedemultiplexerknowwhichgroupof8-digitsrelatestochannel1,2,andsoon?
Clearlythisisimportant!
Theproblemiseasilyovercomebyspecifyingaframeformat,whereatthestartofeachframeauniquesequenceofpulsescalledtheframecode,orsynchronizationword,isplacedsoastoidentifythestartoftheframe.Acircuitofthedemultiplexerisarrangedtodetectthesynchronizationword,andtherebyitknowsthatthenextgroupof8-digitscorrespondstochannel1.Thesynchronizationwordreoccursonceagainafterthelastchannelhasbeenreceived.
UNIT9
GSM(GlobalSystemforMobileCommunication)
Thesuccessofmobilesystemsacrosstheworldisasignthatcommunicationismovingtowardsamorepersonalized,convenientsystem.Peoplewhohavetouseamobilephoneonbusinesssoonbegintorealizethattheabilitytophoneanytime,anyplaceinone’spersonalliferapidlybecomesanecessity,notaconvenience.
Thespeedandrapiditywithwhichthepersonalcommunicationsrevolutiontakesplaceis,unlikefixedtransmissionsystems,highlydependentontechnologyandcommunicationstandards.
Formobilethethreekeyelementstoachievingservicetake-uparethecost,thesizeandtheweightofthephone,andthecostandqualityofthelink.Ifanyofthesearewrong,especiallythefirsttwo,thenmarketgrowthisliabletobeseverelyrestricted.
Thefixedtelephoneserviceisglobalandtheinterconnectionvariesfromcoaxialcabletoopticalfibreandsatellite.Thenationalstandardsaredifferent,butwithcommoninterfacesandinterfaceconversion,interconnectioncantakeplace.Formobiletheproblemisfarmorecomplex,withtheneedtoroamcreatinganeedforcomplexnetworksandsystems.Thusinmobilethequestionofstandardsisfarmorecrucialtosuccessthanfixedsystems.Inaddition,thereisalsothevexedquestionofspectrumallocationinthemobilearea.
Mobilesystemsoriginallyoperatedinanalogmodeinthe450MHzband,movinglaterto900MHzwithdigitalGSMandthento1,800MHzwithpersonalcommunicationsystems.Thehistoryofmobilitycansplitintogenerations.Thefirstgenerationsystemsweretheadvancedmobilephonesystems(AMPS)intheUS,totalaccesscommunicationsystem(TACS)inmostofEuropeandNordicmobiletelephonesystem(NMT);whichwereallanaloguesystems.ThesecondgenerationisvarymuchdominatedbythestandardfirstsetoutinEuropebythegroupspecialmobile(GSM)committee,whichwasdesignedasaglobalmobilecommunicationsystem.
TheGSMsystemisbasedonacellularcommunicationsprinciplewhichwasfirstproposedasaconceptinthe1940sbyBellSystemengineersintheUS.Theideacameoutoftheneedtoincreasenetworkcapacityandgotroundthefactthatbroadcastmobilenetworks,operatingindenselypopulatedareas,couldbejammedbyaverysmallnumberofsimultaneouscalls.Thepowerofthecellularsystemwasthatitallowedfrequencyreuse.
Thecellularconceptisdefinedbytwofeatures,frequencyreuseandcellsplitting.Frequencyreusecomesintoplaybyusingradiochannelsonthesamefrequencyincoverageareasthatarefarenoughapartnottocauseco-channelinterference.Thisallowshandlingofsimultaneouscallsthatexceedthetheoreticalspectralcapacity.Cellsplittingisnecessarywhenthetrafficdemandonacellhasreachedthemaximumandthecellisthendividedintoamicro-cellularsystem.Theshapeofcellinacellularsystemisalwaysdepictedasahexagonandtheclustersizecanbeseven,nineortwelve.
TheGSMsystemrequiresanumberoffunctionstobecreatedforafullyoperationalmobilesystem.
Thecellcoverageareaiscontrolledbyabasestationwhichisitselfmadeupoftwoelements.Thefirstelementisthetransmissionsystemwhichcommunicatesouttothemobileandalsoreceivesinformationfromittosetupandmaintaincallswhenactuallyinoperation.Thebasestationtransceiver(BST)iscontrolledbythebasestationcontroller(BSC),whichcommunicateswiththemobileswitchingcente
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