脉冲位置调制光谱切片传输中英文翻译

Pulsepositionmodulationforspectrum-slicedtransmissionProponentsofultra-wideband(UWB)technologypromisetodeliverlargeamountsofdatawithverylowpowerspectraldensity.Theultra-widebandradioconceptisveryattractiveasitpromisestoopenlargeamountsofspectrumtoavarietyofusersandatthesametimeitclaimslittleinterferenicebetweenusers.Unlikeconventionalwirelesscommunicationssystemsthatarecarrierbased,UWB-basedcommunicationsisbaseband.ItusesaseriesofshortpulsesthatspreadtheenergyofthesignalfromnearDCtoafewGHz.Onetypicaltechniqueistoassignawindowintimeandshifthepositionofthepulsewithinthatwindow.Thisisclassicalpulsepositionmodulation.Withbandwidthrestrictionseffectivelyremoved,UWBpromisestospeedupwirelessdatatransferrates.SomepublishedworkhasaddressedtheissueofhowmanyuserscantheUWBchannelsupport[2][3].Thisworkconsideredonetypeofcapacity-thecapacityintermsonthenumberofusers.Thecapacitywasderivedfromsignal-to-noiseratio(SNR)considerations.AcertainSNRisrequiredtoachieveaspecifiedbiterrorprobability(BEP).Thenoisefloorraiseswiththenumberofusers.AmorefundamentaltypeofcapacityisthewellknownShannoncapacityinbits/s.OurgoalistodevelopanunderstandingoftheroleofvariousparametersontheShannoncapacityofUWBcommunications.ThewellknownShannon!sformulC=Wlog(l+SNR),whereSNRisthe2signal-to-noiseratioandWisthechannelbandwidth,predictsthechannelcapacityCforanadditivewhiteGaussiannoise(AWGN)channelwithcontinuousaluedinputsandoutputs.ThisexpressiondoesnotapplytocommunicationswithPPMsignals.PPmisamodulationwithdiscrete-valuedinputsandcontinuous-valuedoutputs.Furthermore,PPmsignalsareorthogonal,whichimposesanadditionalconstraintonthecapacitycalculations.Newcapacitycalculationsarerequired,whichhtakeintoaccounttheseconstraints.PPMcapacitywasstudiedinthecontextofwirelessinfraredandopticalchannels[4].ThecapacityofPPMmodulationservesasthestartingpointtowhichUWB-specificconstraintsareadded.TheconstraintsarethepowerspectrumdensitylimitationunderFCCPart15rulesandthespreadingratioconstraint.Sincegigahertzunoccupiedslicesofbandwidtharenotavailableatmicrowavefrequencies,underFCCregulations,UWbradiomustbetreatedasspuriousinterferencetoallothercommunicatIonsystems.TheFCCiscurrentlyassessingwhethertoallowUWBemissionsonanunlicensedbasis.UnintendedoutofbandemissionsaregovernedbyFCCPart15rules.Inthispaper,weassumethatUWBtransmissionscomplywiththisFCCrule.Thespreadingratioconstraintisintendedtosatisfyinterferencesuppressionrequirements[5][6].Thispaperisorganizedasfollows.Sectionintroducesthesignalmodel.ThelinkbudgetcalculationforUWBunderFCCPart15rulesisdevelopedinsection.AnalysisofUWBM-aryPPMcapacityiscarriedoutinsectionIV.Finally,conclusionsareprovidedinsectionV..SIGNALMODELConsiderasingle-userUWBpulsepositionmodulatedcommunicationssystem.TheM-aryPPMsignalsetis{S1(t),S2(t),SM(t)},whereSm(t),(mM)Canbewrittenas:(t)=p(t-j).Inthisexpression,p(t)istheUWBpulseofdurationTp(normalizedsuchthat),Epistheenergyperpulse,Tisthepulserepetitiontime,thesequencecjfrepresentsthetimehoppingcode,withcjTanadditionaltimeshifttothejthpulseoftheccommunicationburst.ForafixedT,thesymbolrateR=1/(N,Tf)determinesN,thefnumberofpulsesthatformasymbol.ThesymboldurationisthenT,=N,Tf.Theparameteristheadditionaltimeshiftcorrespondingtothepulsepositionmodulation,mwithT=0,T<T<T,!-,<T<Tvariouswaveformshavebeenproposedfor112SM-1MS.impulseradioincludingGaussianpulse,Gaussianmonocycle[l],Rayleighmonocycle[7].Allofthesewaveformsreflectthehigh-pass-filteringimpactofthetransmitterandreceiverantennas.Amongthem,theGaussianmonocycleisquiteoftenassumedasaUWBwaveform.Fig.1showsaGaussianmonocyclewitheffectivepulsewidthTp=1ns,wheretheeffectivepulsewidthisdefinedasthetimeinterval,whichcontains99.99%ofthetotalenergyintheGaussianmonocycle.Ingeneral,inchoosingawaveform,thegoalistoobtainaflatfrequencyspectrumofthetransmittedsignaloverthebandwidthofthepulseandtoavoidaDCcomponent.Itshouldbenotedthatinpracticalsystems,thepulseshapeisconstrainedbyFCCregulation47CFRSection15.5(d),whichhstatesthat!(R)!(R)IntentionalradiatorsthatproduclassBemissions(dampedwave)areprohibited!±Without,lossofgenerality,wemakethefollowingassumptions:1.Notime-hoppingcodeisused,c3=0.2.TheUWBpulsebandwidthWisrelatedtoitstimedurationTasc/T,wherecisthepptime–bandwidthproduct.3.LetthespreadingratioTf/TpbeequaltoP.Inpreviouswork[5][6],wehaveshownthatthespreadingratioplaysanimportantroleindeterminingthejamresistanceofanUWBcommunicationsystem.Typicalvaluesare>100.ThebandwidthrequirementsofM-aryPPMcanbeestimatedfromtheLandau-Pollaktheorem[8],whichhstatesthatthebandwidthofasignaltimelimitedtoT,(symbolduration)andofdimensionalityMisapproximatelyB=.ThisvaluecanbeinterpretedastheminimumbandwidthrequiredtotransmituncodedM-aryPPM.UWBusingMaryPPMisspreadspectruminthesensethattheUWBbandwidthW>>B.From(2),W=c/Tp,andT,=NT,thespreadspectrumconditionWsf>>Bismetforaspreadingratio=>>M.ThemotivationforspreadspectrumUWBPPMistwofold:(1)attainspecifiedleveloftransmittedpowersubjecttopowerdensityconstraintssetbyFCCPart15regulation,(2)attainspecifiedlevelofresistancetootheremissionsintheband(jamresistance).Thetransmittedpowerrequirementisdeterminedbythedistancebetweenthetransmitterandthereceiver.Thisissueisdiscussedinthenextsection.JamresistanceofUWBisanalyzed.UWBLINKBUDGETInMay2000,theFCCpublishedaNoticeofProposedRuleMaking(NPRM)toincludeUWBemissionsunderPart15rule.Inthenotice,theFCCtentativelyproposedthatUWBemissionsabove2GHz,shouldcomplywiththeexistingPart15limits,andthatUWBemissionsbelow2GHzshouldbeattenuatedatleast12dBbelowthePart15limits.Inthissectionofthepaper,weassesstherangeofcommunicationusingUWBbycarryingoutlinkbudgetcalculationsassumingcompliancewithFCCPart15rules.Thecommonlyusedlinkbudgetequationcanbeexpressedas:,3wherePtistransmittedUWBpower,Pisreceivedpoweratdistanced.GtandGareantennagainsfortransmitterandreceiverrespectively,bothassumedas0dB.TheexpressionofpathlossPLtobeusedin(3)dependsonthepropagationmodel.Currently,thereisnocommonlyacceptedmodelforUWB.In[9],itwasshownthatinanenvironmentdensewithobscuringobjects,thereceivedsignalstrengthapproximately-4followsd-dependencywithdistanced.Atshortrangesuchasseveralmeters,the-2transmissionisdominatedbythedirectsignalpath(ddependency).ThegeneralUWBpathlossmodelcanbewritten:PL(dB)=10log,wherenisthepowerattenuationexponentandXisthewavelengthcorrespondingtotheworkingfrequencyfc.Theworkingfrequencyisthecenterofbandwidth,anditisassumedtobe2.5GHzforaUWBsignalofbandwidthW=1Ghzoccupyingthefrequencyrangefrom2GHzto3GHz.AccordingtoFCCPart15rules,emissionsabove900MhzshallnotexceedfieldstrengthlevelsofE=500micro-volts/meter/Mhzmeasuredatadistanceof3elationshipbetweenPtandEcandependonanumberofadditionalfactors,acommonly-usedexpressiontoapproximatetheirrelationshipis[10]:.5From(5)andaftersomecalculations,weobtainthetransmittedpowerconstraintforaUWBtransmissionovera1GHzbandwidthis.6Toproperlydetectanddecodethereceivedsignal,thereceiverrequiresacertainminimumSNR.Ifweconsideronlythermalnoiseastheprimarysourceofinterference,thereceivednoisepowerNcanbecalculatedfrom:N=Ktwf,7wherekistheBoltzmann!sconstan1.38xJoules/K,Tistheroomtemperature(typicallytakenas300K),andFisthenoisefigure(optimistically)assumedF=5dB.ForaUWBreceiverwithbandwidthW=1GHz,thecalculatednoiseflooris-89dBm.Unlikeothercommunicationsmethods,whichtransmitcontinuoussignals(100%dutycycle)andthepeakpowerequalstheaveragepower,withUWB,thepulsedurationTpismuchshorterthanthepulserepetitiontimeTf.ThespreadingratioP,whichisdefinedastheratioTf/Tp,Istypicallylargerthan100,resultinginapulsepeakpowerhundredsoftimelargerthantheaveragepower.TheSNRpersymbolattheinputofthecorrelationreceiverisexpressed=2E,/No,whereE,istheenergypersymbolandNoisthenoisepowerdensity.ThesymbolSNRisrelatedtotheaverageSNRasfollows.TheaveragesignalpowerisgivenbyE,/T,WithW=and=,wehavethefollowingexpressionfortheaverageSNRatthereceiver:SNR=,8whereg=2cN.Theparametergplaystheroleofprocessinggain(ratioofthesymbolsSNRavailableatdetectiontotheaverageSNRatthereceiverinput).Itfollowsthattherequiredsensitivityofthereceiverisgivenby:S=N+F+SN,9whereSNRistherequiredsignaltonoiseratioandallquantitiesareexpressedindBmDordB.Inordertogetthedesiredperformanceatadistanced,theminimumreceivedsignalpowershouldbeequalorlargerthanthesensitivity,viz.,dS.From(3)and(9),wecangetrelationsbetweensystemparameterssuchasthespreadingratiopandthemaximumcommunicationsrange&ax.Fig.2demonstratesthetrade-offbetweendatarateandrangeofanuncoded,1GHzUWBcommunicationsystemutilizing2-PPMmodulation.Thefigureshowsthemaximumrange(subjecttoFCCPart15emissionrestrictions)atwhichtherequiredsignaltonoiseratioSNRisstillmetasafunctionofD-6thedatarate.TheSNrrequirementiscomputedforBEP=10ThecurvescorrespondDtodifferentpathlossfactors.NotethatinordertomaintainthesameBEPastherangeincreases,theprocessinggainghastoincrease.Sinceg=2cNandforafixedSbandwidth,thisleadstolowerdatarates(eitherthroughhigherframedurationTftoincrease==,orthroughincreasedNsnumberofUWBpulsespersymbol).Forexample,utilizinganUWBbandwidthof1GHz,arateof25Mbit/sisavailableat20mforapowerattenuationfactorofn=4oratarangeof490mforafactorofn=2.Whilethissectiondealtwiththelinkbudgetforuncodedcommunications,thenextsectiondiscussesthecapacityofUWBcommunications.IV.UWBCHANNECLAPACITYThewellknownShannon!sformulC=Wlog(l+SNR),whereCisthecapacityin2bits/sandWisthebandwidth,appliestotheAWGNchannelwithcontinuous-valuedinputsandoutputs.ThisisnotthecaseforPPM-UWB,whichhasadiscrete-valuedinputandacontinuous-valueoutput.ThecapacityofPPMorthogonalsignalsovertheAWGNchannelwascomputedin.ThereferenceservesasastartingpointinthecomputationofthecapacityofUWBsignals.58Forthediscrete-valuedinputandcontinuous-valuedoutputchannelshowninFig.3,akk-bitinformationsourceU=(U,U,U,!-,ismappedtoaM=2PPMsignalsetX=123kX,X,!-,,whereeverysignalX,canberepresentedasanM-dimensionalvector12Mmx,.ThesignalconstellationofXisinterpretedasacollectionofpointsinmM-dimensionalsignalspacewithonepointlocatedoneachcoordinateaxisatadistanceofafromtheorigin.ThevectorrepresentationofX,isgivenbyx=(0,!-,0,0,!-,0.mThismodelholdsforanysetofM-aryorthogonalsignals,withenergyEperdimensionalssymbol.CapacityisthemaximumamountofinformationthatcanbetransmittedreliablyandisgivenbyC=maxI(Y,U),whereI(Y;U)isthemutualinformationbetweenthepUchanneloutputYandthechannelinputU,p(U)istheM-arysourceprobabilitydistribution.SinceXisaninvertiblefunctionofU,thecapacitycanbeexpressedC=maxpI(Y,U).Inaddition,sinceM-aryPPMconsistsofsymmetricalorthogonalsignals,Xcapacityisachievedwithauniformsourcedistribution,pX=x=1/M,form=1,..,M.mWhensuchsignalsaretransmittedovertheAWGNchannelwithtwo-sidednoisespectraldensity=,thecapacityCasafunctionofthechannelsymbolSNRM-PPMpisgivenby[4]][bits/symbol],wheretherandomvariablesvm=1!Mhavethefollowingdistributionconditionalmonthetransmittedsignalx1(duetothesymmetryofM-aryPPM,anysignalcanservetoconditiontheoutput):ThesymbolN(m,1)denotestheGaussiandistributionwithmeanmandvariance1.ThechannelsymbolSNRpthusservestheroleofafter-demodulationSNR.Tomake(10)applicabletoUWB,itisnecessarytocustomizetheexpressionofpforUWB.From(3),(4)and(9),underFCCPart15rules(constrainedtransmittedpoweraspertheprevioussection)theSNRatdistancedfromtheUWBtransmittercanbewritten:SNR,11wherektisaconstantthatdependsonthetransmittedpowerconstraint,receiverantennagain,andcenterfrequency.Tomeettherequiredperformanceatdistanced,SNRSNR.DThesymbolSNRp,canbeexpressedasafunctionofmaximumcommunicationsdistancebylettingthesignaltonoiseratiobethesmallestallowed,i.e.,SNR=SNRD.Itfollowsfrom(8),=2c,12whereallquantitiesweredefinedpreviously.Fig.4presentsthecapacityinbitsperPPMsymbolofUWBasafunctionofthesymbolchannelSNRasper(10)forvariousnumberoflevelsM.ThecurveswereobtainedbyMonteCarlorunsof(10).Forreference,thepointsofuncodedM-aryPPMcorrespondingtoabiterrorprobabilityofarealsoshown.FromthefigureitcanbebservedthatthegapbetweenuncodedM-aryPPMandcapacityis3-6dB.Thisgapistheimprovementthatcanbeobtainedwithcoding.TheseresultsarevalidfortheAWGN.Thespectralefficiencyinbits/s/Hzcanbeobtainedfrom(10)asfollows:59==[bits/s/Hz].13Notethatincreasingthespreadingratiophastheeffectofreducingthespectralefficiency.Fig.5and6weregeneratedusing(13)inconjunctionwith(12)andshowtheupperboundonthespectralefficiencyasafunctionofrangeforaUWBsubjecttoFCCPart15emissionsconstraints.Thesystemassumptionsusedinthelinkbudgetoftheprevioussectionapplyhereaswell.Fig.5wasgeneratedwithapowerattenuationexponentn=4,whileinFig.6n=2.From(12)and(13),itcanbeobservedthatcapacityisdependentontheproductg=c.Bothfiguresweregeneratedwithg=100.ThesefigurescanbeusedtopredicttheupperboundontheperformanceofUWBsystems(meetingFCCPart15requirement)overtheAWGN.Withapowerattenuationexponentofn=4(Fig.5),a-2spectralefficiencyof5xl0bits/s/Hzcanbeobtainedatadistanceof10metersusing32-PPMsignalling.Withapowerattenuationofn=2(Fig.6),thesamespectralefficiencyextendstoabout75meters.Asanotherexample,fromFig.6,fora1GHzchannel,therangeofcommunicationsisupto75metersforadatarateof50Mbits/sandupto325metersforadatarateof10Mbits/s.Thesefiguresprovideonemoreillustrationofthetrade-offbetweendatarateandrangeofcommunications.A.ComparisonofUWBandDS-SSanChannelCapacityCommunicationsutilizingUWBanddirect-sequencespreadspectrum(DS-SS)signalsaresimilarinthesensethatbothuseashortpulse(PNchipinDS-SS)togetthespreadspectrumeffect.But,therearefundamentaldifferencesbetweenthetwosystems.TheUWBsystemisworkingwithoutacarrierandthepulsesemittedbythetransmitterarediscontinuous.Conversely,DS-SSsignalsarecontinuousandwithaninformationwaveformmodulatedbyaspreadspectrumwaveformandacarrierfrequency.WithtraditionalDS-SS,thewidebandwidthisachievedbymodulatingthedatamessagewithapseudonoise(PN)sequence.TheprocessinggainisobtainedasaresultofthePNpropertyandthenarrowchipofthemodulatingsequence.UnlikeDS-SS,thespreadbandwidthoftheUWBwaveformisgenerateddirectlyandnotbymodulationwithaseparatespreadingsequence.TheprocessinggainofUWBisduetotheextremelyshortpulse,whichgeneratesaverywideinstantaneousbandwidthsignal,andisachievedatthereceiverbytime-gatingmatchedtothepulseduration.Furthermore,themodulationformatsusedinthetwosystemsaredifferent.M-aryPSKinDS-SSsystemisasingleortwodimensionalmodulation,whileM-aryPPMinUWBsystemisM-dimensional.Bydefinition,spreadspectrumisinefficientfromthepointofviewofthespectralefficiencyofasingleuser.Aspreviouslymentioned,itsapplicationinUWBismotivatedbytheneedtokeepthepowerspectraldensitylowandtolimittheeffectofinterference.Similarly,inDS-SS,spreadspectrumisnecessaryforinterferencesuppression(whichleadstotheabilityofmultipleuserstosharethebandwidth).ItisinstructivetocomparethecapacitiesofUWBandDS-SS,eventhoughthetwosystemhavedifferentmechanismofspreadspectrum.ForaUWBsystemutilizingM-aryPPMandaDS-SssystemwithM-aryPSK,thedifferenceincapacityisduetothedifferentmodulationformats.Thecapacityofadiscrete-valuedinputandacontinuous-valuedoutputAWGNchannelwithMaryPSKmodulationwasanalyzedin[11].Fig.(7)showsthecomparisonbetweenthecapacityofUWBasper(10)forM-aryPPMandthecapacityofDS-SSasper[11,(5)]forM-aryPSK.CapacitiesofbothsystemsareplottedasafunctionofSNRp,e.g.,UWBandDS-SShavethesamepowerconstraint.ItisobservedthatathighSNRp,bothsystemshavesimilarcapacities.ForlowSNR,andwiththeexceptionofM=2and60M=4,UWBhasahighercapacitythanDS-SS.ForexampleforM=32,toachieveacapacityof5bits/symbol,theminimumrequiredSNRforDS-SSisabout30dB.ThesamecapacitycanbeobtainedbyUWBforonly=15dB,againof15dB.ForM=2andM=4,thesituationisreversedwithDS-SShavingaslightadvantageofabout2.5dB.脉冲位置调制光谱切片传输超宽带（UWB）技术的承诺下付出大量的数据非常低功率谱密度的支持者。超宽带无线电的概念是非常有吸引力的，因为它承诺各种用户砂打开大量的频谱，同时它声称小用户之间的干扰不错。不像传统线通信系统，舰载，基于UWB的通信基带。使用SASE一系列短脉冲传播你NERGY信令从接近DC到几GHz的成分股。一个典型的技术是，签署一个窗口，在时间和SHIF的脉冲，在该窗口中的位置。这是经典的脉冲位置调制。随着带宽限制，有效地去除，UWB有望加快电子线数据传输高铁酸盐。有些酒吧已发表的工作已经解决的问题，有多少用户可以UWB信道支持。这项工作视为一种类型的能力的能力interms数量的用户容量是来自信号没有ERATIO（SNR）的注意事项。宏基包含SNR须达到指定的biterr或概率（BEP）。本课题主要完成PPM的调制与解调。课题的研究PPM调制的基本原理及数学模型。阐述了PPM的基本原理并建立其数学模型。其中介绍了单脉冲位置调制（PPM）﹑差分脉冲位置调制（DPPM）和多脉冲位置调制（MPPM）的基本原理,并对几种调制方式进行比较,最终应用单脉冲位置调制（PPM）进行调制电路的设计。简单的介绍了一下MATLAB与Simulink,并利用其进行PPM调制电路的设计,进而进行仿真,得到仿真波形。提供访问网络传输容量利用波分复用技术已经成为核心网络的速度增加了越来越重要的。低成本的方法是可取的,有一种可能性是以一个使用光学滤波器的宽带噪声源窄片,方法通常被称为谱或谱切片（SS）。这提供了一个具有成本效益的替代激光二极管源源不连贯了但强度过量的鼻子。一个原始的分析提出了频谱分割（SS）采用数字脉冲位置调制（PPM）和传输的最大似然检测。治疗是放置在低成本接入网络的背景下,在系统参数允许的高斯近似的就业。ss-ppm相比,通断键控（ss-ook）在分散的存在和发现是一些典型的2-4分贝更敏感。此外,与激光基于OOK,最佳ss-ppm配置减少或消除SS功率损失进行了比较。调制与解调是大气激光通信中的一项关键技术，目前的大气激光通信系统大多设计为开关键控(OOK)和曼彻斯特编码等强度调制/直接检测方式(IM/DD)，这种调制解调方式虽然实现简单，但其抗干扰能力差，为了进一步提高传输通道抗干扰能力，可以采用脉冲位置调制(PPM)方式，该调制方式相对于OOK等其他调制方式具有低的平均功率，较高的峰值功率，具有编码简单，能量传输效率（每光子传输的信息量）高的优点。兼备安全隐蔽和信噪比高的特性，因此PPM调制技术在自由空间通信(FSO)中被广泛采用。本文主要介绍了PPM调制技术在激光通信中的应用、原理及其Matlab与QuartusII的仿真实现。其中首先阐述了此种调制方式发展的现状及其在空间激光通信领域中的应用前景，分析了其主要的技术性能和特点，介绍了PPM调制方式的基本概念及其在激光通信中的应用。然后具体对3种PPM调制方式进行了分析，并将他们与OOK调制作了比较，对比了他们在激光通信中的优缺点：虽然PPM提高了对频带宽度的要求，但他的能量利用率比较高，抗干扰能力比较强。文中介绍了MATLAB的发展应用及SIMULINK动态仿真的基本知识，给出了任意2n进制PPM调制的设计和基于MATLAB的仿真。在VerilogHDL部分的设计中首先对FPGA进行了介绍并对QuartusII软件和VerilogHDL语言也做了一定的介绍，之后对所做的调制系统进行介绍并对仿真波形进行解释。最后，对PPM这种调制方式作了展望并且分析了其中有待改进的部分。所谓激光通信，是指利用激光束作为载体进行语音、数据、图像信息双向传送的一种技术，它采用信道编码技术以改善通信的质量。激光具有扩散小，相干性和方向性好，光束功率密度大等优点。因而适合于保密通信和航天通信，与无线电微波通信相比，激光通信由于其通信容量大，发射天线体积小，抗射频，抗电磁脉冲干扰以及反窃听性能好，特别是抗核破坏能力等优点备受军事和航天领域的青睐。利用光波作为信息载体进行光通信的历史由来已久。早在一百多年前贝尔就获得了光通信的专利。在两次世界大战中也先后出现过光通信机，但采用的都是普通光源，光的单色性、方向性和相干性都很差，调制和接收也很困难，从而限制了光通信的发展。激光通信依据传输技术的不同，又分为四种：光纤通信、大气通信、空间通信、水下通信。目前，大气激光信系统多采用强度调制/直接检测IM/DM方式。应用于IM/DD系统的调制方式有很多种，常用的有OOK(开关键控)、PPM(脉冲位置调制)、DPIM[10](数字脉冲间隔调制)和DPPM(差分脉冲位置调制)等。最一般的形式是开关键控(OOK)和曼彻斯特编码。在OOK系统中，通过在每一个比特间隔内使光源脉冲开或关对每个比特进行发送。这是调制光信号最基本的形式，只需通过光源闪烁即可完成编码调制。开关键控OOK调制方式具体地分为非归零NRZ(NotReturnZero)码与归零RZ(ReturnZero)码两种编码格式。OOK调制方式的NRZ码是在“1”比特时间间隔内发送光脉冲，在“0”比特时间间隔内不发送光脉冲；RZ码则是在“1”比特的前半个时间间隔内发送光脉冲，在“0”比特时间间隔内不发送光脉冲。因此，NRZ码与RZ码的比特速率是相同的，但是RZ码的激光器调制速率高，较NRZ码节省一半的功率。在曼彻斯特编码中，序列中每一比特由2个开关脉冲组成。通常，光源由编码脉冲波形进行强度调制，同时直接检测接收机对强度调制后信号进行解码，是大气激光通信系统调制方式中最简单、最一般的方式。但是它的功率效率很低，受背景光的影响较大，信噪比很难提高，在光信号经过长距离的大气衰减后己经变的很微弱的情况下，这种调制方式无法保证通信的可靠性与全天候，且通信速率很难提高，不能很好的发挥光通信的频宽优势。DPIM调制方式中每个符号所包含的时隙数是变化的而不是固定的，并可分为无保护时隙和有保护时隙两种。有保护时隙的DPIM调制方式大多采用一个保护时隙，这样能有效地减少码间串扰的影响，该调制方式的符号SK(k为符号所表示的十进制数)的时隙个数为k+2，脉冲在每个符号的起始时隙上，后加一个保护空时隙，再加上k个空时隙表示信息。当接收端解调时，在判断接收到脉冲时隙后，只需要数脉冲时隙后的空时隙个数，再减1就可以了。因此DPIM在接收端只需要时钟同步而不需要符号同步，大大简化了系统的实现。在PPM(PulsePositionModulation)系统中，采用断续的周期性光脉冲作为载波，载波受到调制信号的控制，脉冲时间位置随之发生变化而传递信息。简单来说，它是一种使激光器发射的激光脉冲的调制方式。在激光通信中，采用PPM调制方式可以在给定的激光脉冲重复频率下，用最小的光平均功率达到最高的数据传输率，理论上可达1000Mb/s。这大大降低了对激光器发射功率的要求。当然PPM也存在一定的缺点，比如提高抗干扰能力的同时，付出的代价是增加了对带宽的需求。毕业设计(论文)外文资料翻译系别：电子信息系专业：通信工程班级：B090310姓名：田家丰学号：B09031017外文出处：Hindawi附件：1.原文；2.译文2013年03月基于C8051F单片机直流电动机反馈控制系统的设计与研究基于单片机的嵌入式Web服务器的研究MOTOROLA单片机MC68HC（8）05PV8/A内嵌EEPROM的工艺和制程方法及对良率的影响研究基于模糊控制的电阻钎焊单片机温度控制系统的研制基于MCS-51系列单片机的通用控制模块的研究基于单片机实现的供暖系统最佳启停自校正（STR）调节器单片机控制的二级倒立摆系统的研究基于增强型51系列单片机的TCP/IP协议栈的实现基于单片机的蓄电池自动监测系统基于32位嵌入式单片机系统的图像采集与处理技术的研究基于单片机的作物营养诊断专家系统的研究基于单片机的交流伺服电机运动控制系统研究与开发基于单片机的泵管内壁硬度测试仪的研制基于单片机的自动找平控制系统研究基于C8051F040单片机的嵌入式系统开发基于单片机的液压动力系统状态监测仪开发模糊Smith智能控制方法的研究及其单片机实现一种基于单片机的轴快流CO〈,2〉激光器的手持控制面板的研制基于双单片机冲床数控系统的研究基于CYGNAL单片机的在线间歇式浊度仪的研制基于单片机的喷油泵试验台控制器的研制基于单片机的软起动器的研究和设计基于单片机控制的高速快走丝电火花线切割机床短循环走丝方式研究基于单片机的机电产品控制系统开发基于PIC单片机的智能手机充电器基于单片机的实时内核设计及其应用研究基于单片机的远程抄表系统的设计与研究基于单片机的烟气二氧化硫浓度检测仪的研制基于微型光谱仪的单片机系统单片机系统软件构件开发的技术研究基于单片机的液体点滴速度自动检测仪的研制基于单片机系统的多功能温度测量仪的研制基于PIC单片机的电能采集终端的设计和应用基于单片机的光纤光栅解调仪的研制气压式线性摩擦焊机单片机控制系统的研制基于单片机的数字磁通门传感器基于单片机的旋转变压器-数字转换器的研究基于单片机的光纤Bragg光栅解调系统的研究单片机控制的便携式多功能乳腺治疗仪的研制基于C8051F020单片机的多生理信号检测仪基于单片机的电机运动控制系统设计Pico专用单片机核的可测性设计研究基于MCS-51单片机的热量计基于双单片机的智能遥测微型气象站MCS-51单片机构建机器人的实践研究基于单片机的轮轨力检测基于单片机的GPS定位仪的研究与实现基于单片机的电液伺服控制系统用于单片机系统的MMC卡文件系统研制基于单片机的时控和计数系统性能优化的研究基于单片机和CPLD的粗光栅位移测量系统研究单片机控制的后备式方波UPS提升高职学生单片机应用能力的探究基于单片机控制的自动低频减载装置研究基于单片机控制的水下焊接电源的研究基于单片机的多通道数据采集系统基于uPSD3234单片机的氚表面污染测量仪的研制基于单片机的红外测油仪的研究96系列单片机仿真器研究与设计基于单片机的单晶金刚石刀具刃磨设备的数控改造基于单片机的温度智能控制系统的设计与实现基于MSP430单片机的电梯门机控制器的研制基于单片机的气体测漏仪的研究基于三菱M16C/6N系列单片机的CAN/USB协议转换器基于单片机和DSP的变压器油色谱在线监测技术研究基于单片机的膛壁温度报警系统设计基于AVR单片机的低压无功补偿控制器的设计基于单片机船舶电力推进电机监测系统基于单片机网络的振动信号的采集系统基于单片机的大容量数据存储技术的应用研究基于单片机的叠图机研究与教学方法实践基于单片机嵌入式Web服务器技术的研究及实现基于AT89S52单片机的通用数据采集系统基于单片机的多道脉冲幅度分析仪研究机器人旋转电弧传感角焊