基于FPGA的chirp通信系统的调制与解调技术毕业设计.docx

基于FPGA的chirp通信系统的调制与解调技术毕业设计.docx

《基于FPGA的chirp通信系统的调制与解调技术毕业设计.docx》由会员分享，可在线阅读，更多相关《基于FPGA的chirp通信系统的调制与解调技术毕业设计.docx（24页珍藏版）》请在冰豆网上搜索。

基于FPGA的chirp通信系统的调制与解调技术毕业设计

编号：

毕业设计（论文）外文翻译

（原文）

学院：

信息与通信学院

专业：

通信工程

学生姓名：

李忠斌

学号：

1000210219

指导教师单位：

信息与通信系

姓名：

樊孝明

职称：

讲师

2015年6月8日

InvestigationofmodulatorchirpandextinctionratioindifferentRZ-andNRZduo-binarytransmittermodulesforperformanceoptimization

Abstract-Inthisworkwepresentacomparativeinvestigationofmodulatorchirpandextinctionratioindifferenttransmittermodulesfor10Gbps,20Gbpsand40GbpsRZ-andNRZduo-binarytransmission.Forcomparativeanalysisthreetypesoftransmissionmoduleshavebeenconsideredviz.push–pullconfigurationbasedondualarmMZIM,delay-and-addcircuitbasedsinglearmMZIMandaduo-binaryfilterfollowedbysinglearmMZIM.Foreachcase,themodulatorchirphasbeenoptimizedwithanextinctionratioof20dB.InvestigationhasbeencarriedouttofindextinctionratioofsinglearmMZIMusedforRZ-andNRZduo-binarytransmissionthatofferssystemperformancecomparabletodualarmMZIMat10,20and40Gbps.Theresultshelpchoosingthebestsuitabletransmittermodulewithoptimizedmodulatorchirpandextinctionratio.

I.INTRODUCTION

Inhighspeedopticalcommunicationsystemsduo-binarymodulationisaneffectivesolutionthatprovidesabetterspectralefficiencyandreducestheperformancedegradationowingtodispersionandnonlineareffects[1–3].Inthe1980sandtheearly1990s,directmodulationofsemiconductorlaserwasthemostlyusedtechnique.However,directmodulationhasseverallimitingfactorslikeitinducesunwantedchirpswhichresultsinspectrabroadeningofthesignal,hencecausingseveredispersionpenalties[4].Directly-modulatedopticalsignalsexperiencefluctuationsinintensityduetoRelativeIntensityNoise（RIN）ofthesemiconductorlaser.Nonzerolinewidthoflasersourcesintroduceslaserphasenoisethusforhighspeedtransmissiondirectmodulationisusuallynotpreferred.Hence,externalmodulationhasbeenanessentialchoiceforthehighspeedlong-haulcommunication[5,6].Externalmodulatorsremovethelargeamountofwavelengthchirpingwhichwillotherwisebeincludediflaserdiodeisdirectlymodulated.Mainlytwotypesofsemiconductorexternalmodulatorsareavailableviz.Electro-OpticModulator（EOM）andElectro-AbsorptionModulators（EAM）[6].Ofthesetwomodulators,EOMthatchangesthebandgapenergywithappliedelectricfieldismostlypreferredbecauseofvariousadvantageslikelinearresponsecharacteristic,highextinctionratio,abilitytocontrolphase,frequencyoramplitudeofthelightwavecarrierowingtothepropertiesofelectroopticmaterial.EvenforverylowvalueofdrivingvoltageEOMisabletoachievehighspeedmodulation[7,8].

II.Theory

Inopticaldomain,datamodulationisachievedusingtwotypesofmodulators:

opticalphasemodulatorandopticalintensitymodulator.AnElectro-OpticPhaseModulator（EOPM）usesonlyoneelectrode.Whenadrivingvoltageisappliedtotheelectrode,therefractiveindexoftheelectro-opticwaveguidechangesaccordingly,thusslowingdownthelightwaveandhenceinducingadelayontheopticalsignal.Theinduceddelaycorrespondstothephasechange,thusanEOPMisabletomanipulatethephaseofthelightwavecarrier[9].

whereVπisthedrivingvoltagerequiredtocreateaphaseshift,V（t）isatime-varyingdrivingsignalvoltageandVbiasisdcbiasvoltage.OpticalfieldEoattheoutputoftheEOPMisgivenas:

Eo（t）=Ei（t）ejϕ（t）

（2）

OpticalintensitymodulatorusestwoEOPMsinaparallelstructuretoformaMach–ZehnderinterferometercommonlyknownastheMach–Zehnderintensitymodulator（MZIM）[9].InputopticalsignalsplitsequallyinthetwoarmsoftheMZIMwhichareactuallyEOPMsformodulatingthephaseoftheopticalcarrier.Attheoutput,thetwoarmsarecoupledeitherconstructivelyordestructivelytoprovideintensitymodulatedopticalpulses.

Fig.1.Duobinarytransmittermodulewithdual-armMZIM（T#1）.

Fig.2.Duobinarytransmitterwithsingle-armMZIMdelay-and-addcircuit（T#2）.

Fig.3.Duo-binarytransmitterwithsingle-armtransmitterandfiltercircuit（T#3）.

MZIMcanbeoftwotypes:

single-armMZIManddualarmMZIM.Insingle-armMZIMonlyonesingledrivingvoltageisappliedtotheeitherarmofMZIM[9]andtheoutputtransmittedopticalfieldEo（t）isgivenas:

ExistenceofthephaseterminEq.（3）showsthatthechirpingeffectispresent,thuswecansaythatthesingle-armMZIMgeneratedsignalsarenotchirp-free.ParticularstructureoftheMZIMcanonlyminimizethechirping（x-cutMZIM）.Ithasbeenfoundthatasmallamountofchirpisusefulfortransmission[9].Dual-armMZIMhaspush–pullarrangementwherethedualdrivevoltagesV1（t）andV2（t）areinversetoeachotherandthus,abletocompletelyeliminatethechirpingeffectinthemodulation.Thetransmittedopticalfieldcanbewrittenas:

Fig.4.Comparisonof10GbpsRZduo-binarytransmittermodules

Fig.5.Comparisonof20GbpsRZduo-binarytransmittermodules.

Theuseofopticalduo-binarytransmitterwiththedual-armMZIMistheusualchoiceintransmitterdesignathighdatarate,however,dualarmconfigurationdemandsmorestringentrequirementofsymmetrytobemet[10].Single-armMZIMwithduo-binaryfiltercanalsobeusedwhereduo-binaryfiltercanbeapproximatedbyalowpassfilterwithhalf-powercutoffatapproximatelyonefourththedatarate.Atthiscutofffrequency,thespectraloccupancyofthemodulatedopticalfieldisrestrictedto[f0±（Bitrate）/2],wheref0isanominalcontinuouswave（CW）frequency[11].Thefrequencyspectrumofanidealduo-binarysignalexhibitsthefirstnullsat[f0±（Bitrate）/2].So,wecanband-limitthesignalat[f0±（Bitrate）/2]whilepreservingatthesametime,sufficientinformationforlaterreconstructionofthesignal[11].Theduo-binaryfilterusedforsimulationisafifthorderlow-passBesselfilter.Duo-binarysignalgenerationcanalsobeachievedbydirectlyapplyingtheRZ/NRZsignaltothedelay-and-addcircuitfollowedbybandlimitingfilterofbandwidth（Bitrate）/2.

III.Performancemeasure

IV.Systemdescriptionandresults

Aperformancemeasurecriterionprovidesustheplatformforinvestigationandanalysis.Inthisworkwehaveconsideredthesemi-analyticBERevaluationtechniquefortheestimationoftheBitErrorRate（BER）andBERequivalentQ-factorisconsideredasperformancemeasurecriterion.

Inthepresentanalysis,weareconsideringthreetypesofduo-binarytransmittermodulesviz.

（1）duo-binarytransmitterbasedonpush-pullconfigurationofdual-armMZIM（hereafterdenotedbyT#1）,

（2）single-armMZIMwithdelay-and-addcircuit（hereafterdenotedbyT#2）and（3）thesingle-armMZIMfollowedbyaduo-binaryfilter（hereafterdenotedbyT#3）.SimulativeanalysishasbeenperformedusingcommercialpackageOptSimTM.Wecarriedoutouranalysisatthreedifferentbitratesof10,20and40Gbps.Thesimulationsetuptypicallycomprisesofthreesections:

duo-binarygeneration,i.e.transmittersection,opticalfilterorchannelandthereceiversection.Receiversectionwhichiscommoninthelinkdesignforallthreeabove-mentionedtransmittermodulesconsistsofaPINphotodetectorhavingtheresponsivityof0.8A/WfollowedbyafourthorderelectricalBessellowpassfilterof30GHzbandwidthcenteredat1550nmwhichprovidesfiltereddatatotheBERestimatorforperformancemeasurement.WeoptimizethemodulatorchirpCforallthreetransmittermodulesatanExtinctionratioof20dB.TofindthevalueofCthatoptimizessystemperformance,wevarytheCvaluefrom-4to+2.Fig.1showsthesimulationsetupofNRZduo-binarytransmissionusingT#1module.OpticallinkconsistingofSingleModeFiber（SMF）of80km,20kmand4kmlengthshavebeenconsideredforduo-binarytransmissionat10,20and40Gbpsrespectively.SMFhasthefollowingspecifications:

attenuationlossof0.2dB/km,dispersionanddispersionslopeof16ps/km-nmand0.07ps/nm2-kmat1550nm,respectively,effectiveareaof80m2andrefractiveindexof2.5×10-20m2/W.SMFisfollowedbyanEDFAthatprovidesafixedpowerof3dBmandhasanoisefigureof4.5dB.Inthissimulativework,anopticallaserhaving10MHzlinewidthhasbeenconsidered.

Tocarryoutsimulation,firstRZduo-binarytransmissionhasbeenconsideredandthentheRZpulsegeneratorinFigs.1–3hasbeenreplacedwithNRZpulsegeneratortoobtainNRZduo-binarytransmission.ForaparticulardatarateoptimalvalueofChasbeenfiguredoutforeachtypeoftransmittermodule.Q-factorofT#1atoptimizedCforextinctionratioof20dBhasbeenconsideredasreferencetocomparewithT#2andT#3.ExtinctionratioatwhichT#2andT#3offerscomparableperformancetoT#1isinvestigated.

Fig.4reportsthatat10GbpsRZduo-binarytransmissions,T#1isoptimizedatC=0.4whileT#2andT#3optimizeat−0.8and−1.4Cvalues,respectively.Itisobservedthatat20dBextinctionratioT#2performsbetterthanT#1andT#3.ConsideringT#1with20dBextinctionratioasreference,itcanbeinterpretedthatT#2achievestheperformanceofT#1atarelativelylowervalueofextinctionratio.

Fig.5recordsoptimumCvalueof0.2,−1.0and−1.6forT#1,T#2,T#3respectivelyusedin20GbpsRZduo-binarydatatransmission.Comparisonofdifferenttransmittermodulesat20dBextinctionratioshowssimilarqualitativebehaviorasseeninFig.4.

Fig.6showsthatCvalueof0.2,−0.6and−1.4ensureshighestQfactorforthethreetransmittermodulesrespectively.At40GbpsRZduo-binarytransmittedfromT#1providesbetterperformancethanT#2andT#3.TheperformanceofT#1at20dBextinctionratiocanbeachievedat