《光纖通信課程設(shè)計(jì)》課件：Class12-03

FiberOpticNetworkDesignX.Wu,M.Y.Li,C.S.YanDept.ofOpt.Engr.,ZJU2011Class12Topic:OCDMA

OCDMAhistoryFiberOCDMACode&DecodeImplementationbyFBGExerciseCDMAIntroduction–

TheacronymCDMA=CodeDivisionMultipleAccess

分碼多重存取式

CDMA：展頻系統(tǒng)，展頻系統(tǒng)將傳輸資訊(通常是語(yǔ)音)所需的頻寬展開(kāi)極寬頻，可讓同頻或是鄰頻使用者所造成的干擾減至最低CDMA由指定不同的手機(jī)使用不同代碼的方式，允許多個(gè)使用者在同一時(shí)間使用同一個(gè)頻道CDMAIntroduction–

TheHistory1985ITU-FPLMTS(FuturePublicLandMobileTelecommunicationsSystems)成立1991Qualcomm發(fā)表一套CDMA系統(tǒng)測(cè)試結(jié)果，是當(dāng)時(shí)AMPS的十倍容量1993IS-95標(biāo)準(zhǔn)正式製定1994FPLMTS改名

IMT-20001997IS-95B標(biāo)準(zhǔn)完成CDMAIntroduction–

ThedevelopmentgroupCDG:CDMADevelopmentGroupTIA:TelecommunicationIndustry

AssociationETSI:EuropeanTelecommunication

StandardsInstituteTl.PG:TelecommunicationPlanningGroupCDMAPrinciples–

一個(gè)好的比喻1/3在室內(nèi)一群參加宴會(huì)的人們-TDMA

CDMAPrinciples–

一個(gè)好的比喻2/3在室內(nèi)一群參加宴會(huì)的人們–FDMACDMAPrinciples–

一個(gè)好的比喻3/3在室內(nèi)一群參加宴會(huì)的人們-CDMAHistoryOverview(CDMA)1938,inthefieldofradarsystems,examplesoffrequencyhoppingsignalpatternswerepatentedDuringandafterWWIIthefactofBWexpansionwithoutpulsenarrowingcouldalsoprovidefinertimeresolution.1950sSolGolombfirstBooksonCDMAEarlysystemareARC-50byMagnavoxandsatelliteradiosaswellasfewGPSsystemsHistoryOverview(OpticalCDMA)RelativelynewtechniqueinOpticalFibercommunicationsandseemstooutperformtraditionalTDMandWDMFirstappliedinmid1980’sbyASalehi

Prucnalandsomeothers.AimforTerabitperformanceonBroadbandNetworksbyreducingthecostofeveryaspectinopticalnetwork.IntroductionCDMAusedextensivelyinradiofrequencycommunicationsystems,especiallyin2Gand3Gcellulartelephonenetworks.BasicAdvantageisthewayithandlesafiniteBWamongalargenumberofusers(moreuserscantransmitthesamedataoverthesameBandwidth)…introduction(comparison)TDMAandWDMAschemespresentsignificantdrawbacksinLocalAreaSystemswhenlargenumberofusersmustbeconsidered.TDMA:oneusertxatatimeSystemcapacity=users*txrateWDMA:Fourwavemixingasdiscussed(nextslide)DrawbacksDWDM(revisited)DispersionAttenuationFourwavemixingNon-linearnatureofrefractiveindexofopticalfiberLimitschannelcapacityoftheDWDMSystemDifficulttoconstructfordynamicsetofmultipleusersbecauseofthesignificantamountofcoordinationamongthenodesrequiredforsuccessfuloperation.…comparisonOpticalCDMAdoesnotneedtimeandfrequencymanagementbecausealltheuserstransmitusingthewholeBWatthesametime!Itcanalsooperateasynchronously(asinwirelessapplications)withoutpacketcollisions.SlotallocationrequirementsarenotneededhereincontradictiontoTDMAandWDMA…comparison(Advantages)Simpleimplementation,usingexistingfibernetworksReducethecostineveryaspect:Equipment,outsideplantFacilities,OperationalSupportsystemsSECURITYEliminatemanyofintermediatetime-divisionmultiplexingstepsrequiredbySONETHowdoeso-CDMAworkTheprincipleisthesameasinwirelessapplication.Eachuserisassignedauniquecode(spreadinglength-L-)whichismultipliedbyeachbit.Thiscodeisonlyknowntothereceiverinordertodemodulatethedata.Themostimportantpartforcorrectdetectionisthecode.Thiscodemustbeuncorrelatedfromotheruser’scodesandbeorthogonal.Multiplicationbyeither+1or-1TwoopticalorthogonalCodewithlengthL=32andλα=λc=1.

Firstcodeisrepresentedbyplacingapulseatthe1st,10th13thand28th

chippositions.Secondcodeisrepresentedbyplacingapulseatthe1st,5th12thand31st

chippositions.OrthogonalCodeexample

…h(huán)owdoeso-CDMAworksO-CDMAdividesthefiberspectrumintoindividualcodes,allderivedfromasinglebroadbandopticalsource(WDMdividesthespectrumintonarrowopticalwavelengths)Itisasimple3–stepprocess:Source–Filter–ModulatorFilter:SpatialFiltercanbethoughtanopticalBarcode(fixedorprogrammable)SpectralCodingSpectralDecodingHowtochoosewavelength/channels=x…DecodingDecoding:X1user:calculater·X1-r·X1=12-8=4unitsofpower->‘1’X2user:calculater·X2-r·X2=10-10=0unitsofpower->‘0’OrthogonalCorrelationFunctionHadamardCodeBERv.s.numberofgratings(chippositions)andusersNumberofchipsNumberofUsersOnewaytosavethenumberofgratings:ModifiedDoubleWeightCode(MDW)

-sharedwavelengthOnlycorrelatedch