通信工程专业英语论文.doc
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通信工程专业英语论文.doc
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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
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