直接序列扩频通信dsss.docx

直接序列扩频通信dsss.docx

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直接序列扩频通信dsss

直接序列扩频通信（dsss）

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2005issuenumberfourth:

1001-893X（2005）-0128-0403

Thematicreview

SUMMARIZATION

AccuratemeasurementmethodofPNcodephaseindirectsequencespreadspectrumcommunicationsystem

HuXiulin,ZhangJun,YangLing

*

（Departmentoftelecommunication,HuazhongUniversityofScienceandTechnology,Hubei,Wuhan430074）

pick

ThispaperpresentsamethodforaccuratelymeasuringthephasedifferencebetweenthelocalPNcodeandtheinputPNcode,whichcombinesnumericalanalysis

Algorithmanddigitalsignalprocessingtechnology,andbymeansofthephaseunitoutputvaluehasahighmeasurementprecision,andthemethodforfulldigitalmethod,canuseFPGAandDSPprocessingchipconveniently.Theresultsofcomputersimulationaregiven,andtheaccuracyandnoiseimmunityofthismethodareanalyzedbysimulationresults.Thismethodisofgreatvalueinpseudocoderanging,highprecisionPNcodeacquisitionandtracking,differentialpositioning,andsoon.Keywords:

spreadspectrumcommunication;codephase;PNleastsquaresmethod;graphclassificationnumber:

TN914.42;documentidentifiercode:

A

A,Method,for,Accurately,Measuring,the,Phase,of,PN,Code,,in,DSSS,Systems

HU,Xiu-Lin,ZHANG,Jun,YANG,Ling

（HuazhongUniversityofScienceandTechnology,Wuhan430074,ChinaAbstract:

methodaccuratelymeasuringthe）forphaseerrorbetweenthelocalPNcodeandthereceivedAPNcodeisstudied.ThismethodisacombinationofnumericalanalysisalgorithmandDSPtechnology.Itanalysestheoutputofphaseerrorunittogainhigh-accuracy.Besides,itisaalldigitalmethodwhichcanberealizedconveniently.Theaccuracyandtheantiperformanceofthemethod-noiseareanalyzedbasedontheresultofcomputersimulation.Thismethodisofgreatvalueinthefieldsofpseudorandomranginghighpseudorandomacquisitionand-accuracytracking,differentialorientationandsoon.Keywords:

SpectrumspreadcommunicationPhase,of,PN,code,Least,squares,method,thisphasedifferencecannotbemeasureddirectlyandaccuratelybynumericalmethods.However,insomeapplications,suchassatellitedifferentialpositioning,itisnecessarytoknowpreciselythevalueofthisphasedifferencetoimprovethepositioningaccuracy.Afulldigitalmethodformeasuringthisphasedifferenceispresentedinthispaper.

I.citation

word

Indirectsequencespreadspectrum（DSSS）communicationprocess,inordertomakethelocalPNcodeandinputPNcodesynchronization,thereceiverneedstocaptureandtracking,toenterthePNcodewhenthelocalPNcodeandPNcodeinputphasedifferenceiswithintherequiredrange,webelievethatthetransmitterandthereceiver,thePNcodehasbeentoachievesynchronization.Evenwhenthetrackingloophasreachedasteadystate,thereisalsoaphasedifferencebetweenthelocalPNcodeandtheinputPNcodeduetoloopnoiseandotherreasons.Attheusualsamplingfrequency,

Two.Phasediscriminationunitandphaseerrorcurve

Theschematicdiagramoftheleaddelayphasediscriminatorusedinthemethodisshowninfigure1.

*

Receiveddate:

2004-08-19

128?

2005issuefourth

Thematicreview

SUMMARIZATION

Figure1

Principleblockdiagramofphasediscriminationunit

TheinputsignalofthediscriminatorunitshowninFig.1isthebasebandsignalx（n）.Inthecaseofnonoiseeffects,theexpressionsfortheX（n）areB,B,X（n）=A,K,PN,nT,s）,-j2,PI,Delta,fnT,s（E,B

（1））

TPNforwhichAKistheinformationcode,sisthesamplingperiodofthesystem,（nT,s）PNcodediscretetime-domainexpression,fistheresidualfrequencydeltadifferenceafterdownconversion.Remember,thelocalpseudorandomcodePNnTS+Kee（K）forthelocalphasedifference,PNcodeandPNcodeinputaheadofthelocalPNcode1/Tc+KE）behindthelocal,2ChipPNcodePNnTS+2（PNcode1/2ChipPNcodePNnTs（Tc+Ke）.Base2

Figure2P（k）Kefunctionrelationande

Three.CodephasemeasurementmethodPN

ReceivertocapturetheinputPNcode,thecapturesucceeded,thelocalPNcodeandinputPNcodephasedifferenceislessthanTC/2.ThereceiverthentracksthephaseoftheinputPNcodesothatthephasedifferencebetweenthelocalPNcodeandtheinputPNcodeislessthanTC/8.Itisthenpossibletoestimatetheresidualphasedifference.ThephasemeasurementmethodforthePNcodeisshowninfigure3.

WithsignalrespectivelywiththeforwardandbackwardPNmultiplication,eachmultiplicationresultsrespectivelyinacumulativeinformationelementineveryway,relatedprocessingaftertheresultswererecordedasR+k）-K（R）,and（,

N-1

R+（k）=R-（k）=

PN,B,sigma,X（n+kN）（nTs,N,=0）

N-1

+-

Tc+Ke）2Tc+Ke）2

（2）

PNsigmax（n+kN）（nTs,B,N,=0）

Intheform,Nisthenumberoftimesofeachinformationsymbol,=thelettercodecycle,N/samplingperiod.（andthesquareofthemodulus,thenR+k）,R-K）makesthedifferencebetweenthetwosquarestoobtainthedesiredphaseerrorvalue.ThephaseerrorvalueexpressionforP（k）=R（k）-||2-|+R（k）|2eTcTc=R2（K-E）-R2（K+e）（3）PNPN22

Fig.3blockdiagramofphasemeasurement

（thefunctionRPNtau）PNcodeautocorrelationfunction:

R,PN）=EPNt（T）,PN（+）,andP（（k）Kefunctionapproximatefigure2e

[1]

Firstofall,NCOcodePNcodeintothefixedsteplength（variablemoduluscounternoadjustmentstep）andapluralityofphasedemodulationunit,withadifferentphaseofthePNcode,atthesametimeextractionphaseandenterthePNcode129?

?

（4）

.

In2005fourththedifferenceoperation,resultingindifferentphaseerror,andthephaseerrorintheoryshouldbeshowninFigure2ofthephasecurve.SincetheenvironmentalprotectioncertificatetracksthelocalPNcodeandtheinputPNcode,thePNphasedifferenceusedbyeachphasediscriminatorislessthanTC/8,andthephasedifferencebetweenthecodephaseandtheinputPNcodeisnogreaterthanTC/2.Whentheaboveconditionsaremet,thephaseerrorcurve,whichisintendedtobederivedfromthemeasuredphaseerrorvalue,mustbeastraightlinesegment,correspondingtofigure2-TC/2toTC/2.ThenthephasedifferencebetweenthelocalPNcodeandtheinputPNcodecanbemeasuredonthebasisofthezerocrossingoftheproposedandphaseerrorcurve.InFigure3,thephaseerrorvalues1~7arePe1toPe7,respectively.Irrespectiveofthenoise,thePe7isthepointonthephasediagramPe1

（2）.Affectedbynoiseinterference,thePe1toPe7willdeviatefromthereferencephasecurve.ThephasedifferencebetweenthePNcodephaseandthelocalPNcodeusedbyeachdiscriminatorunitisx,sothatthephaseerrordifferenceisy,andthecoordinatesystemisestablishedbyusingXasthehorizontalaxisandtheverticalaxis,

Pe1~Pe7correspondstotheYpointcoordinateswere3Tc/16,Pe1（Tc）-/8（Pe2）（Tc/16,Pe3（0）,Pe4（Tc）/16,Pe5）,（Tc/8/16（3Tc,Pe6）Pe7）,.Accordingtothese7coordinates,theleastsquaresmethodisusedforlinefitting,asshowninfigure4.ThecoordinatesofthelocalPNcodeinthiscoordinatesystemare0,whiletheinputPNcodecoordinatesofthelineandtheaxisoftheintersectionofRcoordinates.Thus,theabscissavalueoftheintersectionofthelineandaxisrepresentsthephasedifferencebetweenthelocalPNcodeandtheactualreceivedPNcode.^e=P

MI=12I

Thematicreview

SUMMARIZATION

NoticethatthexIintheformulaissymmetricabouttheorigin,sigmax,I=0,i.e.

I=1M

Therefore,formula（5）canbefurthersimplifiedinto

MM

X0=-

Sigmay,I,sigma,x2i,I,=1,I,=1

M

（6）

Msigmax,I,y,I

I=1

Intheformula,thesigmaxisonethatcanbecalculatedinadvance,oftenbecauseofthenumber,sothecalculationformulaisnotlargeenoughtobeimplementedwithhardware.

Four,antinoisemeasuresinengineeringimplementation

Itcanbeprovedthatthemethodproposedinthispaperisaunbiasedestimationmethodforphasedifference,andthroughsomesimplemeasures,theaccuracyofphasedifferencemeasurementandthenoiseimmunitycanbeimprovedsignificantly.Inengineeringimplementation,theaveragevalueofphaseerrorshouldbeusedtofitthecurve,whichisusedtoapproximatethephaseerroroftheerrorcurve.Theeshouldbetakenasfollows:

P

L,e,sigma,P（k）,K,=1

L

（E）=EP（k）

（7）

Forexample,eachphaseunitwillgetaphaseerrorresultsinaninformationsymbolperiod,L=100100yuanwilltaketimecodeinformationinthephaseoftheaverage,withtheaveragevalueofcurvefitting,wecaneffectivelyimprovetheantinoisemeasurecan.

Five、numericalsimulationandperformanceanalysis

Inthesimulationprocess,severalimportantparametersusedinthenumericalsimulationofthesamplingrateis16timesthefrequencyofPNcode;numericalsimulationwithPNcodefor9Goldcode,usedtogenerateacompositepolynomialmsequenceGoldcodeforthisoptimizationandinitialphaseasshownintable1.Table1generatespolynomialandinitialphase

Initialbinary）（101101111111100101）

Msequencenumbergenerationpolynomialbinary）（M1graph4,thelocalPNcodeandtheactualreceivedPNcodedifferenceintime,M21001011001,1000010001

Thezerocrossingerrorofphasediscriminationerroriscalculatedbytheleastsquaremethod,andtheresultsareasfollows:

x0:

MMMM

Inthenumericalsimulation,differentsignal-to-noiseratiosarechosentostudytheeffectsofnoise

X0=-

Sigmay,Isigma,x2i-Sigma,x,I,sig