通信工程专业英语论文.doc

通信工程专业英语论文.doc

《通信工程专业英语论文.doc》由会员分享，可在线阅读，更多相关《通信工程专业英语论文.doc（7页珍藏版）》请在冰豆网上搜索。

姓名:

高炜班级：

通信工程2班学号：

10021340208

AtmosphericLaserCommunication

Keywords:

AtmosphericlasercommunicationModulationTransmitReceiveApplication

Abstract：

AtmosphereLasercommunicationisoneofnewcommunicationtechnologies，asaresultofmanyadvantagessuchaslargemessagecapacitances，thebestconfidentialityandsimpleequipmentandsoon，whichwouldtriggerarevolutionofnewcommunicationtechnology.Thepurposeofthispaperistoexploretheelementsoftheatmosphericlasercommunication，advantageanddisadvantageoflasercommunication.

Maintext：

Therehasbeentremendoustechnicaladvancementofavailablecomponentssuchaslaser/LEDtransmitter,highsensitivityopticalreceiverofferingextremelyhighbandwidth,efficientmodulationtechniques,improvementinlowpowerconsumption,weight,andsize.Inspiteofmanysuchtechnologicaldevelopments,themajorlimitationoffree-spacelasercommunication（lasercom）performanceistheatmosphere.Atmosphericconditionultimatelydeterminesthelasercommunicationssystemsperformancenotonlyofterrestrialapplicationsbutalsoforuplink-downlink（e.g.,betweengroundandsatellite,aircraftorUAVterminals）,becauseaportionoftheatmosphericpathalwaysincludesturbulenceandmultiplescatteringeffects.

Atmosphericlasercommunicationtechnologyisanewtechnologyappearedrecently.Theelementofthenewtechnologyisthatopticalsignalcarriertransmitsthesignalpointtopointorpointtopointsbyatmosphere.Thistechnologyusesemiconductorlaserastheopticalsource，whichformsacommunicationsystemnameddigitalradiocommunicationsystem.Lasercommunicationsystemincludetwoparts：

TransmittalandReception.TransmittalcontainsLasers,opticalmodulatorandopticalemittingantenna.Andreceptioncontainstheopticalreceivingantenna,opticalfiletandopticaldetector.Themessagesweneedtotransmitconnecttolasersinopticalmodulatorandopticalmodulatormodulatesthemessagestolaserandtransmittedbytheopticalemittingantenna.Atthereceivingend,theopticalreceivingantennareceiveslasersignalandsendthesignaltoopticaldetector.Theopticaldetectortransformsthelasersignaltoelectricalsignalanddemodulateselectricalsignaltooriginalmessagesafteramplification.

Theprimaryfactorscharacterizinganatmosphericcommunicationchannelincludeatmosphericattenuation（frombothscatteringandabsorption）andscintillation.Attenuationoftheopticalwave（i.e.,reductionofitspower）byatmospherecanbecausedinseveralways,includingabsorptionoflightbygasmoleculesandRayleighorMiescatteringbygasmoleculesoraerosolparticlessuspendedintheair.OpticaltransmissionspectrumoftheU.S.StandardAtmosphereoverthevariouscommunicationwindowsisavailableintheliterature.[1]Theindividualabsorptionlinesarecausedbythevibration-rotationalabsorptionlinesofwatervapor,CO2,CH4,andothergasesofminorconstituentsintheatmosphere.Scatteringfromaerosolsandparticulatessuchasinfog,clouds,smoke,anddustalsocontributetothetotalattenuation

Oftheopticalbeam.

1、Thecomponentofatmosphericlasercommunicationsystem

Atmosphericlasercommunicationsystemconsistsoftwocommunicationmechanism，whichtransmitmodulatedlaserpulsesignal（voiceordata）reciprocally，receivinganddemodulatingthesignalemittedbyeachother，achievingduplexcommunication.

a）Opticalmaser

Opticalmasergenerateslasersignalandformsbeamintospace.Thequalityofopticalmaserdirectlyinfluencesthecommunicationqualityandcommunicationdistance.Itcancausegreateffecttosystemperformance.

b）ModulatorandModulationmethod

Modulationisthataddingsignalintosignalcarrier.Modulationisakindofphotoelectricconverter,whichisaprocessthatoneparameter（intensity,frequency,phaseposition,polarization.etc）ofoutputbeamchangeswithelectricalsignal，finishingmodulationoflaser.Themodulationmethodshaveinternalmodulationandexternalmodulation.Theinternalmodulationisthataddingtheelectricalsignalmodulatedbyinformationsignalintolaser，makinglasertransmitslightsignalchangedwithinformationsignal.Theexternalmodulationisthatputtingthemodulationunitsoutofthelightsourceandaddingtheelectricalsignalmodulatedbyinformationsignalintomodulationcrystal.Whenlightbeamthroughthecrystal,oneparameter（intensity,frequency,phaseposition,polarization.etc）changeswiththeelectricalsignalchanging.Thenitbecomeslightsignalcontainedinformation.Regardlessofinternalmodulationorexternalmodulation,everymodulationmethodhasitsowndifferentmodulationformssuchasPulseamplitudemodulation,pulsewidthmodulationandpulsefrequencymodulation.Inaddition,directlymodulationalsocontainspulsecodemodulationandexternalmodulat