SINGLE

V_01.21No.4JOURNALOFELECTR0NICS(CHINA)July2004

    ;SINGLEToNEJAMMINGELIMINI’IoNSCHEME

    ;oFMUUI’ICARRIERSPREADSPECTRUMSYSTEM1

    ;YingXiaofanChuZhenyongTianHongxinYiKechu

    ;(StateKeyLabofIntegratedServiceNetworks,XidianUniv.,XiNn710071) ;“(TheTelecommunicationEng.Institute,AirForceEng.Univ.,Xi’an71O077)

    ;AbstractTheproposedschemeisbasedonDiscreteFourierTransform(DFT)domainpro? ;cessing.Thekeytechnologyofthisschemeisjammingparameters’accurateestimationand

    ;jammingreconstruction.Comparedwiththe”thresholdexciser”schemei.theproposedscheme

    ;caneliminatemorejammingenergyonthewholefrequencybandwiththeminimumlossofuse—

    ;fulsignalenergy.Asshownintheresearchandsimulation,theproposedschemeismuchbetter ;thanthe”thresholdexciser”scheme,especiallyinthecaseofhighpowerjammingwhereasthe

    ;“thresholdexciser”schememightbeinvalid.

    ;KeywordsJammingelimination;Transformdomain;Multicarrierspreadspectrum;Single ;tonejamming

    ;I.Introduction

    ;MultiCarrierSpreadSpectrum(MCSS)techniquehasattractedmuchinterestforits ;highspectrumefficiency,jammingrejectioncapability,securityandsoon[一驯.Transform

    ;domainprocessingisanimportantanti-jammingmethod[51.”Thresholdexciser”isaclass[一

    ;calanti-jammingschemebasedontransformdomainprocessing.MCSSsystemusesDiscrete ;FourierTransform(DFT)tododemodulation,sotransformdomainbasedanti-jammingpro—

    ;cessingissignificant[6,’,whichcancooperatewithdemodulationverywellandimprovethe

    ;systemperformancewithlittlecomplexityincreasing.However,ifthefrequencyofjamming ;isnotthesameasoneofthesubcarriers,”spectrumleakage’’occurs[引,thejammingenergy

    ;willspreadtothefrequencybinofallthesubcarriersbecauseofthefinitelengthofsampling ;window.”Thresholdexciser”canonlyeliminatepartofthejammingenergyandtheenergy

    ;lossofusefulsignalofcorrespondingfrequencybinisinevitable,sotheperformanceofthe ;“thresholdexciser”isrestricted.Thereby,anovelsingletonejammingeliminationscheme

    ;isproposed,whereinthekeytechnologyisaccurateestimationofjammingparametersand ;jammingreconstructionwiththeDFTresultofdemodulation.Thenewschemeherecan ;eliminateallthejammingenergythatspreadtoallthefrequencybinsbecauseof”spectrum

    ;leakage”andminimizethelossofusefulsignalenergy.Comparedwith”thresholdexciser’’

    ;scheme,thenewschemehasmuchbetterperformance.

    ;Thisletterisdividedintofivesections.InSectionII.thesystemmodelisdescribed.In ;SectionIII,thenewschemeofjammingeliminationispresented.InSectionIV,simulations ;arecarriedouttocomparetheperformanceofnewschemewiththe”thresholdexciser”

    ;scheme.Finally,wesummarizeourresultsinSectionV.

    ;II.SystemModel

    ;Thediscretebasebandmodulationsignalcanbeexpressedas

    ;Manuscriptreceiveddate:December29,2003;reviseddate:March5,2004. ;SupportedbytheNationalNaturalScienceFoundationofChina(No.60172029)

    ;

    ;NO.4SINGLETONEJAMMINGELIMINATIONSCHEME323

    ;M—l

    ;s()=p(i—KM)?c(m)e陪m

    ;m=0

    ;(1)

    ;whereMhenumberOfsubcarrs,p():{17’,c(m)hePN

    ;codeanddisthe七一thsymbolinformation.Thediscretebasebandmodulationsignalis

    ;thendigital—to—analogconvertedtoanalogsignalS(！).Thereceivedbasebandsignalcanbe ;characteredas

    ;n(t)=s(t)+n(t)+J(t)(2)

    ;wheren(t)istheAdditiveWhiteGaussianNoise(AWGN),J(t)isthesingletonejamming

    ;whichcanbeexpressedas

    ;J(t)=AeJ(&件)(3)

    ;Aistheamplitude,,Jisthefrequencyandistheinitialphaseofthejammingsigna1.R(t)

    ;issampledtobethediscretesignalR(f)denotingthe/-thsampleofthe七一thcodesigna1.

    ;ThenthesamplesareSerially—to-Parallelly(S/P)convertedandM—pointsDFTisdoneto ;getthechipinformation.ChipinformationaremultiplexedbyPNcodetogetdk(m),which

    ;callbegivenby

    ;M，1

    ;(m)=c(m)?Rk(1)e—J备(4)

    ;Finally(m)aresumedupandjudgedtogetsymbolinformationdk ;dk=Judge

    ;(,m=0

    ;cm

    ;)

    ;whereJudge(?)denotesthejudgementfunction.

    ;III.NewJammingEliminationScheme

    ;DFTDomainProcessing

    ;WeCaneasilyjudgewhethersingletonejammingexistsby ;oldexciser”determinesandcutstheworstinfectedfrequency

    ;threshold,whichCanbeexpressedas

    ;d(m):fdk(m),LU,

    ;Basedon

    ;(5)

    ;theDFTresult.”Thresh—

    ;binswhosepowerexceeds

    ;Idk(m)I<threshold(k)

    ;ldk(m)lthreshold(k)(6)

    ;wherethethreshold(k1iSthethresholdofk—thcode.

    ;However.’’spectrumleakage’’constrainedtheperformanceof”thresholdexciser”.

    ;“Thresholdexciser”canonlyeliminatepartofthejammingenergywiththecostofuse

    ;fulsignalenergyloss.SoanewjammingeliminationschemeisproposedasshowninFig1. ;First,thejammingparametersincludingfrequency,amplitudeandinitialphaseareaccu—

    ;ratelyestimatedutilizingDFTresult.Thenthejammingisreconstructedbytheparameters ;estimated.Finally,jammingiSeliminatedonDFTdomain.

    ;Becauseofthe”spectrumleakage”andrestrictedresolvingcapability,wecannotget

    ;theaccurateparametersofjammingsignaldirectlyutilizingDFTresult.FromtheDFT ;1nformationwecanonlydirectlygetthecursoryvalueofjammingparameters[引.Wefocuson

    ;theaccurateestimationofjammingparametersbyusingtheDFTinformationtodofurther ;

    ;324JOURNALOFELECTR0NICS(CHINA)Vl01.21

    ;—

    ;To(01

    ;—一Rk(1)r=:一

    ;SIPfc(1)?Judge一，I

    ;Ll…Jam似m眦ing叵—9一lestimationll……一……’I—

    ;Fig.1Newjammingeliminationscheme

    ;computation.First,weanalyzetheDFTcomputationofsingletonejammingsigna1.When ;demodulation1wesamplethereceivedanalogsignalatthesamplingrateoflstogetdigital ;signal,andinterceptthedigitalsignalbyrectanglewindowoflengthM.Theintercepted ;digitalsignalJd(n)is

    ;(n):J(n)p(n)(7)

    ;whereJ(n)isthediscretesequenceof(t),p(n)istherectanglewindowfunction,whose ;DiscreteTimeFourierTransform(DTFT)P(ej)isIs]

    ;P(ej,:e-J(M一)/

    ;whereisthenormalizedanglefrequency.

    ;ofsingletonejammingis

    ;2sin(wM[2)

    ;sin(w/2)(8)

    ;:2Try~{sIfdenotesthefrequency.TheDTFT

    ;J(ei):AeJ~5(w—uJ)(9)

    ;where.,isthenormalizedanglefrequencyofjammingsigna1.

    ;Becausegd(n)istheintercepted(n),theDTFTofJd(n)istheconvolutionofJ(ej) ;andP(e5),expressedas

    ;Jd(ej,=AeJCe—j(一J)(M一)/

    ;WecanfurtherdeducetheDFTofJd(n)

    ;2sin【(—wg)M/2】

    ;sin[(w一~j)/2】

    ;Jd-DFTcm,=AeJCe-jTr(m-ma)(M-1)/M

    ;(10)

    ;(11)

    ;wheremj:MfJ|{8.

    ;Therefore,if{3isintegertimesof{3,inotherwords,thefrequencyofjammingsignal ;isthesameasoneofthesubcarriers,theJd—DFT(m)hasonlyonenon—zerobinwhichCan

    ;actuallyreflecttheamplitude,frequencyandinitialphaseofjammingsigna1.Otherwise,

;thejammingsignalparameterscannotbeaccuratelyestimatedasshowninFig2.Anovel

    ;estimationalgorithmisproposedinthislet’ter,whichusesthetwoJd—DFT(m)binsthat

    ;havethelargestabsolutevaluetodofurtherprocess.Wedefinethebinpossessingthe

    ;largestenergyasthemainpeak,denotedby1,thebinpossessingthesecondlargestenergy

    ;asthesecondpeakldenotedbyY2.ThelocationofthemainpeakisL=roundM{1||1

    ;whereround(?)istheroundfunction.TheerrorbetweenLandthepeaklocationintheory

    ;mj=M|JfjsisAL(0sAL0.5.

    ;First,wethinkaboutthesituationthatthelocationofthemainpeakishigherthan

    ;thatofthesecondpeak.UnderthissituationthelocationofthemainpeakisLandthe

    ;

    ;No.4SINGLETONEJAMMINGELIMINATIONSCHEME325

    ;1Ymax

    ;/I

    ;,I

    ;,I

    ;,’

    ;,’

    ;t

    ;.

    ;L一2L—lmiLL+l

    ;Fig.2TheabsolutevalueofsingletonejammingDFTJd-DFT(m) ;一

    ;Yl=AeJCe-j~(L-mJ)(M:-I)/M

    ;训AeJCe-jr(L-1-rnj)(M.1)/MJ

    ;?=eJe—J7r?L(M—1)/M五sin(~rAL)

    ;2=e一L-l1)sin[~r(AL-

    ;1)

    ;1)]

    ;Fromtheequationabove,wecanget

    ;Yl—

    ;Jsin[~r(AL一1)/M]J

    ;ly2lIsin(~rAL/M)I

    ;Because~r(AL一1)/Mand~rAL/Marebothverysmall,

    ;(13)

    ;(14)

    ;sin(~rAL/M

    ;一

    ;~rAL/M}(15))?J

    ;Eq.(14)Canbesimplifiedas

    ;?

    ;II

    ;Letr=fylf/ly2f,ALcanbecalculatedby

    ;?(17)

    ;Sothepeaklocationintheorycanbeestimatedby

;mj.est=L一?(18)

    ;Ifthelocationofthemainpeakislowerthanthatofthesecondpeak,thelocationofthe ;mainpeakisLandthelocationofthesecondpeakisL+1,thepeaklocationintheoryCan ;beestimatedas

    ;mI,.est=L+?L(19)

    ;

    ;326JOURNALOFELECTR0NICS(CHINA)VO1.21

    ;Thel3canbededucedas

    ;{{(20)

    ;FromEq.(13),theamplitudeAandinitialphaseofthejammingsignalcanbecalculated ;aLS

    ;A=IYlsin(nAL/M)

    ;sin(hAL)

    ;=angle(?eJ7r?L’M—lM)

    ;whereangle(?)isthefunctionforcalculatingtheangleofcomplex. ;Withthejammingparametersbeingestimatedaccurately,we

    ;jammingsignal,andeliminateitfromthereceivedsignalafterwards ;IV.SimulationResult

    ;(21)

    ;(22)

    ;couldreconstructthe

    ;Simulationsarecarriedouttoevaluatetheperformanceofthejammingelimination ;scheme.ThenumberofthesubcarriersiS128andtheDFTsizeiS128.The/?0iS12dB.

    ;InFig.3.wecomparetheBERperformanceofthe”thresholdexciser’’andthenew

    ;scheme.Wherein,curveBiStheBERperformancewithoutjammingelimination.CurveC ;andcurveDaretheBERperformanceof”thresholdexciser”respectivelyunderthethreshold

    ;3timesand2timesofaverageabsoluted(m).CurveEiStheBERperformanceofthenew ;scheme.TheBERcorrespondingtocurveCandcurveDare4.4×10—and6.5×10一

    ;whenJSRiS25dB.whichindicatethe”thresholdexciser”iSvalidwhenJSRisnotveryhigh

    ;andthethresholdselectedgreatlyinfluencestheperformanceof.

    ;jammingelimination.Ifthe

    ;JSRbeingincreasedto40dB.theBERcorrespondingtocurveCandcurveDare0.1565 ;and0.14.theperformanceisverybadandthereiSonlylittledifierencebetweenthem,which ;indicatethat”thresholdexciser”becomesnearlyinvalidunderthissituation.Ifusingthe

    ;newschemetoeliminatejamming,thereisnOerrorbitin2000000MonteCarloexperiments ;whenJSRiSlowerthan98dB.theBERiSstilllowerthan10—whenJSRiS106dB,which

    ;provesthatthenewschemeproposedinthisletterhasgoodperformance.Thenewscheme ;caneffectivelyeliminatesingletonejammingofveryhighpower,itsperformanceismuch ;betterthanthatofthe”thresholdexciser”.

    ;10.

    ;l0一l

    ;l0—2

    ;重l0-3

    ;lO—

;l0—5

    ;lO_6

    ;20406O8OlOOl2Ol40

    ;JSR(dB)

    ;Fig.3BERperformanceundersingletonejamming

    ;

    ;NO.4SINGLET0NEJAMMINGELIMINAT10NSCHEME327

    ;V.Conclusion

    ;TheDFTofsingletonejammingisstudied,whichisaclassicalproblemofdigitalsig—

    ;nalprocessing.Afterwards,anovelsingletonejammingeliminationschemeofmulticaxrier ;spreadspectrumisproposed.Thenewschemeisbasedonaccuratejammingreconstrunc—

    ;tion,theprocessingcancooperatewiththeDFTbaseddemodulationverywell,SOthe ;complexityincreaseiS~~erylOW.Comparedwiththe”thresholdexciser”scheme,thenew

    ;schemecanperformmu.chbetter.HOWtoreconstructandeliminatemulti—tonejammingiS

    ;aproblemworthyoffurtherstudy.

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