GPS Interceptibility Post-Test Analysis

7/28/2019 GPS Interceptibility Post-Test Analysis

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GEORGIAINSTITUTEOFTECHNOLOGY AUnitoftheUniversitySystemofGeorgia

Atlanta,Georgia30332

cremet*Ttcn mrnmtAmcnIHSTITUTC


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REPORTDOCUMENTATIONPAGE Form ApprovedOMBNo.074-0188Publicreportingburdenforthiscollectionof informationisestimated toaverage1hourper response,ncluding the timeforreviewingnstructions,searching existingdatasources,gatheringand maintainingthe dataneedednd completing an dreviewing thiscollectionof information.end commentsregardingthisburden estimate or anyother aspect ofthiscollectionof information,ncludingsuggestions for reducing thisburdento WashingtonHeadquartersServices,Directorate forInformation Operationsand Reports,1215 Jefferson DavisHighway,Suite1204,Arlington,VA2202-4302,and to the Officeof Managementand Budget,PaperworkReductionProject(0704-0188),Washington,DC 205031.AGENCYUS EONLY(Leaveblank) 2.REPORTDATESeptember 1 ^ 3.REPORTTYPEANDDATESCOVERED FinalReport4.TITLEANDSUBTITLE[GlobalPositioningSystem(GPS)UserEquipmentInterceptibilityPost-TestAnalysis(U) (E)]6 . AUTHOR(S)L.W.PickeringE .J .FainD.C.Chapman7.PERFORMINGORGANIZATIONNAME(S)AND ADDRESS(ES)CommunicationsSystemsDivision,ElectronicsandComputerSystemsLaboratory,GeorgiaTechResearch InstituteAtlanta,Georgia

GeorgiaTech ResearchInstituteGeorgiaInstituteofTechnologyAtlanta,Georgia03329. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)Commander,U.S.NavalSecurityGroup(CNSG)/NavalInformationWarfareActivity(NIWA)Ft.GeorgeG.Meade,Maryland

OPS-3Building 9800SavageRoadFortGeorgeG.Meade,Maryland20755-6000

5. FUNDINGNUMBERSN/A

8.PERFORMINGORGANIZATION REPORTNUMBERProjectA-8348

10.SPONSORING/MONITORING AGENCYREPORTNUMBERN/A

11.SUPPLEMENTARYNOTES Preparedfor:Commander,NavalSecurityGroupCommand,Ft,SecurityGroupActivityNorthwest,Chesapeake,VirginiaMeade,Maryland,andNaval

12a.DISTRIBUTION/AVAILABILITYSTATEMENTUnlimited. 12b.DISTRIBUTIONCODEN/A

13.ABSTRACT(Maximum200Words)ThisdocumentisthefinalreportofthePostTestAnalysis(PoTA)phaseoftheInterceptibility ModuleoftheDataLinkVulnerability AnalysisMethodology(DVAL)asappliedtotheGlobalPositioningSystem(GPS)UserEquipment(UE). TheGPSUEisareceiver-onlysystemandtherefore,thisstudyfocusesonunintentionalemissionswhichmayradiatefromthesystem. ThestudyconcludesthattheprobabilityofinterceptoftheGPSUEemissionsisverylow.

14.SUBJECTTERMS GlobalPositioningSystem,ProbabilityofIntercept,UnintentionalEmissions,GPSUE17.SECURITYCLASSIFICATIONOFREPORTUNCLASSIFIED

18.SECURITYCLASSIFICATION OFTHISPAGEUNCLASSIFIED19.SECURITYCLASSIFICATIONOF ABSTRACTUNCLASSIFIED

15.NUMBEROFPAGES26

16.PRICECODE N/A20.LIMITATIONOF ABSTRACT

ULNSN7540-01-280-5500 StandardForm298(Rev.2-89)Prescribedby ANSIStd. Z39-18

298-102


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INTERCEPTIBILITYPOST-TESTANALYSIS GeorgiaTechProjectA-8348Authors:

L.W.PickeringE.J.FainD.C.Chapman

September1989

Preparedfor:NAVALSECU RI TYG R O UPACTIVITYBuildingNS-84Charleston,SC29408-6200and

NAVALSECU RI TYG R O UPCodeG-853801NebraskaAvenue,NWWashington,D.C.20393-5210

PreparedbyCOMMUNICATIONSSYSTEMSDIVISIONElectronicsandComputer SystemsLaboratoryGeorgiaTechResearchInstituteAtlanta,GA30332


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TABLEOFCONTENTSPage

1.0 INTRODUCTION1.1cope1.2eportOrganization

2 . 0 SUMMARYandRECOMMENDATIONS3. 0 DISCUSSIONOFPOTENTIALEMISSIONSOURCES

3. 1ntentionalEmitters3.1.1elemetry,TrackingandControl(TT&C)Link3.1.2HFCrosslink3.1.3I,L2andL3Downlinks3 . 2 UnintentionalEmissions3.3valuationofUnintentionalEmissions3.3.1valuationof1401.52MHzLOEmissionLevel 03.3.2valuationofthe350.38MHzLOEmissionLevel 33.3.3valuationofthe10.23MHzLOEmissionLevel 44. 0 ANALYSISOFGPSRECEIVERINTERCEPTIBILITY54. 1 FeasibilityofDetection 55 . 0 CONCLUSIONS 0REFERENCES 1

1 1


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FigureLISTOFFIGURES

Page3-1 Rockwell/CollinsUERF/IF/LOarchitecture73-2 LimitforRE02narrowbandemissions125-1 ComparisonofRE02testlevelsvs.EMCONlevels22

LISTOFTABLESTable ^Se4. 1INKANALYSISFOR RECEPTIONOF1401.52MHzLO74. 2INKANALYSISFORRECEPTIONOF350.38MHzLO74. 3INKANALYSISFOR RECEPTIONOF10.23MHzLO7

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1.0NTRODUCTION1.1cope

ThisdocumentisthefinalreportofthePostTestAnalysis(PoTA)haseoftheInterceptibilityModuleoftheDataLinkVulnerabilitynalysisethodologyDVAL)sppliedoheGlobalPositioningSystem( G P S )UserEquipment( U E )developedbyRockwell/Collins.tontinuesndcompleteseorgiaTech'streatmentfomessuesirstddressedndernarlierprogram,ontract68787-86-3383,ndescribedn eportentitled"DVALAssessmentofNAVSTARGPS".hatearlierreportwasthefinalreportforthePre-TestAnalysis( P T A )phaseoftheSusceptibilityandInterceptibilityModulesoftheDVALMethod-ology.

ItshouldbenotedthattheGPSUE,unlikemanyofthedatacommunicationsystemsthatitisreasonabletoevaluatewiththeDVALmethodology,doesnotintentionallytransmitsignals.hus,theInterceptibilitymoduledoesnotplayasbigaroleintheanalysisfGPSammingvulnerabilityastwouldorothersystems.nderthisprogramtheinterceptibilitymodulehasnotbeenemphasizedtothesameextentastheotherthreemodules,whichwillbedocumentedinforthcomingGeorgiaTechreports.

AsspecifiedbytheJointTestForcethatdevelopedtheDVALMethodology,theInterceptibilityModuleisonecomponentinafour-moduleassessmentofthevulnerabilityofradiofrequencydatalinksinanelectroniccountermeasuresenvironment.ntheclassicalcontext,InterceptibilityinvolvesthedeterminationoftheprobabilitythatRFradiationfromacommunicationsystemtransmittercanbedetected,thatthesourceofthatradiationcanbeidentifiedandlocated,andthatthecharacteristicsoftheradiatedsignalcanbeexploitedtodevelopandmountajammingttackgainstheink'seceiver.hisntercep-tibilityanalysisdeviatesfromthisclassicalcontextinthat


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thepecificevicenderonsideration,hePSE,sreceiver-onlyystem.herefore,nanalysisfemissions"focusesprimarilyonunintentionalemissionswhichmayradiatefromtheGPSUE.hevaluefatelliteuplinkemissions,satellitedownlinkemissions,and UHFcrosslinkemissionsisdis-cussed;however,previousdiscussionshaveindicatedthattheseemissionshavelittleornoimpactontheInterceptibilityoftheGPSUE.hisInterceptibilityevaluationreliesprimarilyonanalysis,discussionswithappropriatemilitarytestingagencies,anddiscussionswithRockwell/CollinstestingentitiesnanefforttoassessInterceptibility.talsoprovidesrecommenda-tionsrelativetofurthertesting.1.2 ReportOrganization

Section2.0brieflysummarizesthefindingsofthisreportandssociatedecommendations.ection.0ummarizeshepotentialGPSUEemissionsources,andprovidesabriefsummaryoffindingsfromthepreviousreport.naddition,thissectionfocusesonpotentialGPSUEemissionsthatcouldhypotheticallyprovideforInterceptibilityconcern.ection4.0addressesthefeasibilityofnterceptibilitygiventhepecifiedpotentialemissionsources.ection5.0providesconclusionsanddiscussesrecommendedtestingandassociatedtestingmethodology.oten-tialInterceptibilitytestingthatmaybeincorporatedintotheGPSUEOPEVALisalsoaddressed.


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2.0 SUMMARYandRECOMMENDATIONSFromtheinvestigationdocumentedinthisreport,thas

beenassessedthattheprobabilityofInterceptoftheGPSUEbasedonintentionalsystemandunintentionalUEemissionsisveryow.hiseportaseneratedotentialorstaseInterceptReceiverdetectionrangesbasedontheMIL-STD-461CE06andRE02specifiedallowableupperlevels.Near-FielddeterminedRE02limitsforGPSUEunintentionalemissionshavebeenextra-polatedtotheFar-FieldinanefforttogetanestimateofthepotentialInterceptibilityoftheGPSUE.

Underthefollowingconditions,itisrecommendedthatFar-FieldradiatedpowermeasurementsnotbeperformedtoassessIntercept ibi1ity:

I f ,uringheMI/EMCIL-STD-461pecificationverificationrocess,ear-fieldeasurementsallbelowthespecifiedMIL-STD-461levels.

Ifthesemeasurementsgivegoodindicationthatfar-fieldradiatedlevelsarenotexcessive.

Iftheseconditionsarenotmet,andiftheGPSUEisacceptedwithmissionsbovethepecificationevel,hisituationrelativetoInterceptibility wouldrequireareassessment.


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3.0ISCUSSIONOFPOTENTIALEMISSIONSOURCES3.1ntentionalEmitters

ThissectionbrieflydiscussestheInterceptibilityissuespertainingtotheGlobalPositioningSystemasawhole.nten-tionalemissionsincludethefollowing:Telemetry,Tracking,andControl(TT&C)LinkUHFCrosslinkLIDownlinkL2DownlinkL3Downlink

Previouswork(Section8.0,"DVAL AssessmentofNAVSTARGPS")hasevaluatedhesententionalmissionsithegardonter-ceptibilityoftheGPSasawhole.otethatthesepreviousfindingsindicatedthattheInterceptibilityoftheseintentionalemissionshadlittleornoeffectontheInterceptibilityoftheindividualGPSUEs.hesefindingsshallnowbebrieflysum-marized.3.1.1elemetry.TrackinaandControl(TT&C)Link

ThevalueofinterceptingtheTT&Clinkappearslimited.Jammingtheuplinkappearstobeoflittlevaluebecausethesystemhassuchinherentstabilitythatitcanfunctionformanydayswithoutupdatingorbitalpositiondata,withonlyaslowdecayofGPSUEmeasuredpositionaccuracy.ammingthedownlinkalsoappearsoflittlevaluebecausealternativedownlink/cross-linkpathsanprovideequireddatatotheNetworkControlCenter(NCC).

Greatobstaclesexistevenforhighlycoordinatedjamming,interception,andspoofing.irst,thedataisheavilyencryptedproviding stringent controller/SVDalidationorevent


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spoofing.econd,TT&C ,datatransactionstakeplaceprimarilyovernitedtatesirspace,imitingccessootentialinterceptors/j ammers.

Inaddition,nowledgeofTT&CcommunicationsactivitiesdoesothingoncreaserffecthenterceptibilityfindividualGPSUEs;itistheinterceptibilityoftheUEsthatisemphasizedbytheDVALmethodology.3.1.2HFCrosslink

Utilizingaprioriknowledgeofexactsatellitepositionswouldprovemorebeneficialthanattemptingtodeterminesatel-liteositionsiantegratedransferystemHFrosslinkinterception.

Highlycoordinatedground-basedjammingcouldhypotheticallydisruptUHFcrosslinkinformationtransfer.NodetailshavebeenobtainedregardingGPSspecificinformationtransferredontheUHFcrosslinks,makingdetailedanalysisimpossible.)fUHFcrosslinksprovidearelaynetworkforalmanacdatatransferbetweenGPSsatellites,andthecorrectreceptionofthisdataisdeniedowingtohighlycoordinatedjamming,thenjammedsatel-litesanimplyelynnternallyredictedlmanacataupdatingithittleroverallPSystemerformancedegradation.nddition,ndividualatellitelmanacdataupdatingcanbeprovidedbytheTT&Clinkonceevery24hourperiod.ndertheseassumptions,UHFcrosslinkinterception/jam-mingwould proveoflittlevalue.otealsothatinterceptionofUHFcrosslinkswouldprovidenoinformationaboutthelocationofindividualGPSUEs.3.1.3I.L2andL3Downlinks

FromaGPSUEinterceptpointofview,detailedknowledgeoftheL1/L2/L3signalsonthedownlink wouldnotprovidethejammer


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withnyseful informationertainingoheocationfindividualGPSUEs.

AlthoughknowledgeofthedownlinksignalsdoesnotdirectlyassistinterceptibilityofGPSUEs,hisinformationcouldbeusedyophisticatedeceptionroalledpseudolite"jammers.histopicisaddressedfurtherintheSusceptibilityModulePost-TestAnalysisReport"providedunderthisprogram.3.2nintentionalEmissions

AlthoughtheGPSUEfunctionssolelyasareceiver(andforthatreasoncontainsnodeliberatetransmissionsthatneedtobeassessedrelativetointerceptibility)hereareunintentionallowlevelemissionswhichemanatefrominternalleakagesources.Intheabsenceofdeliberateemissions,thesearetheemissionsourcesthataretheclosesttofallingwithintheintercept-ibilityanalysisconcept.

UnintentionalemissionsfromtheGPSUEreceiversconsistprimarilyofradiatedemissionsfromUEinternalreceiverlocaloscillators.igure3.1illustratesasimplifiedblockdiagramoftheRFportionoftheRockwell/CollinsGPSUE.

AreviewofthisfigureindicatesthatpotentialGPSUElocaloscillatoremissionsourcesconsistofthefollowing:

. 1401.52MHzLO350.38MHzLOReference10.23MHzLOReferenceandHarmonics

Interceptibilitybasedontheanalysisofemissionoftheabovementionedpotentialsourcesfocusesonradiationfromthereceiveantenna,adiationfromRFandIFcablesandconnectors,ndradiationromtheGPSUEaseandomponents.


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I2 X2to1^ C M C D II in

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MIL-STD-461CE06specificationsprovideanupperboundontheallowableunintentionalpowerlevelswhichmayresideattheGPSUEantennaterminal.ikewise,MIL-STD-461RE02specifica-tionsrovidenpperoundnadiationromhePSEsubsystemRFcables,ase,ndcomponents.NOTE:adiationfromtheIFcablesillustratedinFigure3-1arenottestedaspartofthestandardRockwell/CollinsMIL-STD-461verificationprocess.)hisssessmentofnterceptibilityevaluatestheimpactofthese"worstcase"MIL-STD-461specifiedlevels,alongwithknownlevelswhichexistontheIFcables.

StrictualityontrolustetilizednhePSEinstallationprocesssuchthatRFandIFcable/connectorshieldintegrityisverifiedandmaintained.Shielddamageorshieldingdeficienciesouldmpactthedectectibilityofunintentionalemissions,andthisimpactshouldbeevaluated.

Fromhe standpointf Interceptibility, oneusteconcernedftheseunintentionalemissionsareofhighenoughaleveloedetectedandutilizedtoassisthostilejammingefforts.

Itisimportanttonotethatfromapracticalstandpoint,theLOemissionsfromtheGPSUEarelikelytobeminutecomparedtotheradarndommunicationsmissionsromheameplatform.

LimitsnadiatedmissionsndestingcenariosrespecifiedyIL-STD-461ndIL-STD-462,espectively.s-sociatedestsenerallynvolve:)irectlyeasuringhepowerlevelofspuriousleakagecomponentsoninterconnectingleads,nd2 )erformingnear-fieldantennameasurementsinaclosedchamberenvironmenttodetermineradiatedcomponentfieldlevels.


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Unfortunately,heseestsootlwaysivedequateindicationoftheradiatedpowerlevelsinthefar-field.FromthestandpointofInterceptibility,tmustbedeterminedifthesefar-fieldradiatedlevelsarehighenoughtoallowforinterceptndirectionfammingesources,ndetermineWorstCase1limitsonInterceptibility.

IntheflavoroftheDVALInterceptibilityMethodology,thefollowingsectionevaluatesthepotentialimpactoftheabovementionedunintentionalemissions.3.3valuationofUnintentionalEmissions

Thisectionocusesnheeterminationfotentialunintentionalemission worstcaseradiatedpowerlevels.Lackoffar-fieldmeasurementtestdatamotivatessimple

calculationstoassessInterceptibilityowingtounintentionalemissions.hesealculationsaveeenerformednhefollowingfashion:

WorstCaseallowableMIL-STD-461emissionlevelshavebeentilizedorhenintentionalmissionsfinterest.TheseMIL-STD-461levelshavebeenextrapolatedtothefar-field,rovidingor orstasepproximatepotentialfar-fieldradiatedlevel.

.asednheseotentialar-fieldevels,inkanalyseshavebeenperformedinanefforttodetermineathataximumangesnterceptouldotentiallyoccur.

Severalmajorobstaclesexistregardingthisanalysiswhichinclude:


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Nodataexistsrelatedtofar-fieldemissionlevels.Capabilitytomakevalidfar-fieldassumptionsbasedonMIL-STD-461specificationsislimited.Capabilitytoaccuratelydeterminethedegradationinshieldingffectivenessrom ultitudefableshieldingdeficienciesandothershieldingsourcesdoesnotexist.

ThevariousallowableemissionlevelsspecifiedinMIL-STD-461,longwithknownpowerlevelsexistingwithintheRock-well/CollinsGPSUEhavebeenusedtoassistthisanalysisofpotentialradiatedpowerlevels.3.3.1 Evaluationof1401.52MHzLOEmissionLevel

Tobeginthisevaluation,worstcaseMIL-STD-461B(surfaceships)E06limitshavebeenutilized.TheseCE06limitsimplythatconductedemissionsinexcessof34dB^V(narrowband)shallnotappearatthetestsample'santennaterminals.

Assuminga50ohmimpedancefortheRFcablebetweentheGPSantennaandtheAE-4Electronicsassembly,hespecifiedCE06upperlimitmpliesaworstcasepowerlevelf-7 3Bmat1401.52MHz.

CEO6LevelonRFCable: -73dBm( 3 4dB^V)1 )Obviously,theamountofthis'worstcase'potentialpower

thatcouldberadiateddependsonanumberoffactorswhichincludeableength,ablehieldingffectiveness,thershielding,etc.inkanalysisperformedinalatersectionwilltakethesefactorsintoaccount.

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MIL-STD-461BE02imitsorarrowbandmissionsl-lustratednigure-2ndicatehatt401.52Hz,ieldemissionsmustbelimitedto55dB/iV/meter.tshouldbenotedthathisarrowbandE02imitsasedn ear-fieldmeasurementperformedatadistanceof1meter.elatingthemeasurednear-fieldstrengthtothepotentialfar-fieldstrengthcanprovetobeacomplexexercise,soeffortshavebeenmadetodeveloppproximateboundsnthemaximumpotentialar-fieldlevel.

Ifsimplifyingassumptionsareutilized,nindicationofthepotentialfar-fieldstrength[oralternativelythepotentialEIRPEffectivesotropieadiatedower)eneratedromheunintentionalmitter]anbeapproximatedntheupperboundsense.

At1401.52MHz,heallowableMIL-STD-461BRE02narrowbandemissionelectricfieldstrength( EVolts/m)measuredat1meterisspecifiedas:

E=55dB/iV/m=562/iV/m 2 )

Assumingareespaceimpedanceof37 7ohms,heapproximatedpowerdensity( P ( j )associatedwith562/iV/misgivenby:

Pd=E2/37 7=837.78X10~12(W/m2) 3 )

UtilizingtheMIL-STD-462eparationdistanceof1meter,andthevalueofP < jexpressedinEquation( 3 ) ,thepotentialEIRPlevelisgivenas:

RE02EIRPofUnintentionalEmission:-49.77dBm ( 4 )

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MIL-STD-461

cor-I/) E OJo c3 -O3os-s-(C cCM oo

(->r-E CS JI s-3CD

1 2


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Inhisalculation,heE02ieldmissionimitt1401.52MHzasbeenonvertedoanpproximateIRPevelutilizingFarFieldassumptions.Thislevelcannowbeusedtoperforma'worstcase'linkanalysisinanefforttoassessthepotentialInterceptibilityoftheGPSUE.Inthissense,worstcase1isdefinedbasedonthefollowingassumptions:

( 1 )heGPSUEemitsatthespecifiedRE02level.Conver-sationswithRockwell/CollinsindicatethattheGPSUEemitsbelowtheRE02specifiedlevels.)

( 2 )hefarfieldassumptionsinvokedinthederivationoftheadiatedowerevelEIRP)onstitutenp-proximateupperboundontheactualpotentiallevel.

Insummary,ithnoactualmeasuredfar-fielddataonthepotential401.52HzOeakageomponent,herecedingassumedvaluesinEquations1 )nd4 )avebeenutilizedtoassesstheInterceptibilitypotentialoftheGPSUEintheworstcasesense.TheapproximatedEIRPisaconvenientquantityusedinstandardlinkanalysiscalculationswhichfollowinalatersection.3.3.2 Evaluationofthe350.38MHzLOEmissionLevel

The350.38MHzLO,usedinthederivationofthe1401.52MHzLO,istransferredtotheAE-4downconverterfromtheRCVR3A(orRCVR3S)oduleviatheLIIFcable.heactualaveragepowerlevelofthe350.38MHzLOcomponentontheIFcableis0dBm.

ActualLevelonIFCable: 0dBm 5 )TheIL-STD-461BimitorE02arrowbandmissiont

350.38MHzis39dB/iV/m.erformingananalysisofthepotentialEIRPasillustratedinEquations2)-(4),hepotentialworstcase'EIRPat350.38MHzisgivenas:

1 3


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RE02EIRPofUnintentionalEmission: -65.77dBm ( 6 )3.3.3valuationofthe10.23MHzLOEmissionLevel

The10.23MHzLOresidesintheRCVR3A(orRCVR3S)receivermodule.AllUELO'sarederivedfromthis10.23MHzreference.IndditionorivingllystemO's,hiseferencesutilizedtodrivethePandC/ACodeclocks,therefore,thereisapotentialforthis10.23MHzsignaltoberichinevenorderandoddorderharmonics.

ReferringtotheMIL-STD-461BRE02imitsfornarrowbandemissions,thespecifiedlimitat10.23MHzis22d B / i V / m .

PerforminghepproximatenalysissresentednEguations(2)-(4),thepotentialallowableEIRPat10.23MHzisgivenas:

RE02EIRPofUnintentionalEmission: -82.77dBm ( 7 )

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4.0NALYSISOFGPSRECEIVERINTERCEPTIBILITY4.1easibilityofDetection

ThissectiondiscussesthefeasibilityofdetectingtheGPSUEbasedonthecalculatedpotentialworstcaseEIRPlevelsofunintentionalemittersdiscussedintheprevioussection.

Forallthreeunintentionalrequenciesofinterest,hefollowinganalysishasbeenusedtodeterminethemaximumrangethatahypotheticalinterceptreceivermustbefromtheGPSUEinordertoeffectivelyexploitunintentionalemissionsfromtheGPSUE.

Thefollowinglinkequation[ 1 ]willbeusedtoassessthefeasibilityofdetection:( 2 ) dB 01og(EIRP)-20log(47rr/A)+101og(G r/T)-101og(k)-10log(BW)

( 8 )where,

C/NCarrierpowertoNoisepowerRatio( C N R )A =c/f=(2.99x10sm/s)/frequency(Hz)=wavelength

Gr/T=interceptreceiverfigureofmeritk=Boltzman'sconstant

BW=interceptreceivereffectivenoisebandwidthEIRP=assumedpotentialradiatedpowerfromGPSUE

r=maximuminterceptreceiverseparationdistanceforthespecifiedreceivedC/N,receiverGr/T,andapproximatedpotentialemissionEIRP

Forheurposesfhisnalysis,heollowingdditionalassumptionsaremade:

( 1 ) Atmosphericlossesareassumednegligible.15


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( 2 ) Theypotheticalntercepteceiverffectiveoisebandwidthis2kHz.

ThefollowingTables4.1through4.3summarizethemaximumdistancesatwhichthespecifiedhypotheticalinterceptreceiverswillbeabletoperformadetection.

Table4.1summarizestherangerequirementsforaninterceptreceiverwithhepecifiedr/Tigureferit, Hzeffectivereceivernoisebandwidth,ndthespecifiedreceivedCNRfordetectionofthe1401.52MHzLOemission.TwovaluesofCNR(i.e.5and20d B )areutilized.Inthegeneralsense,iftheinterceptreceiverreceivestheunintentionalemissionataCNRof20dB,thentheprobabilityofdetectionisobviouslyveryhigh.Likewise,atareceivedCNRof5dB,theprobabilityofdetectionislow.hevaluesofGr/Tfigureofmerit)sedcorrespondo airlyhighualityntercepteceiver.hecalculatedIL-STD-461BPSUE401.52MHzmissionEIRPf-49.78dBm(-79.78dBW)wasutilizedinthislinkanalysis.otethatasednhepecifiedarameters,heypotheticalinterceptreceivercouldbeasfarawayas10km(line-of-sight) forahighprobabilityofdetection,gnoringtheeffectsofatmosphericattenuation.

AsspecifiedinEquation1 ) ,hepotentialMIL-STD-461BCE06levelofthe1401.52MHzsignalontheRFantennacablemayneverexceed-73dBm(-103dBW).ssumingthatthecableandassociatedfilteringprovidesfora'worstcase'3dBattenua-tion,thenthepotentialEIRPlevelof-106dBWimpliesthatinthe'worstcase'sense,detectioncouldbepossibleatrangesofupto0.5km,asillustratedin Table4.1.napracticalsense,cableshieldingdeficiencieswouldingeneralresultinaworstcase30dBattenuation,insteadofthe3dBattenuationusedinthisanalysis.herefore,nterceptbasedonthisworstcaseCE06levelisvirtuallyimpossible.

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TABLE4. 1LINKANALYSISFOR RECEPTIONOF1401.52MHZLO

LOEIRPRequired

CNR Gr/TMaximum

PotentialRange-80dBW-80dBW106dBW-106dBW

5B20B5B20B20dB20dB20dB20dB

58.0km10.0km2. 9km. 5km

TABLE4. 2LINKANALYSISFORRECEPTIONOF350.38MHZLO

LOEIRP-95.77dBW-95.77dBW-110dBW-110dBW-110dBW

RequiredCNR5dB20dB5dB20dB20dB

MaximumGr/T PotentialRange10dB 12.0km10dB 2. 1km10dB 2.3km10dB . 4km20dB 1.3km

TABLE4. 3LINKANALYSISFORRECEPTIONOF10.23MHZLO

LOEIRP 113BW -113BW -113 dBW

RequiredCNR20dB5dB20dB

Gr/T10dB 1 0dB10dB

MaximumPotentialRange10.0km5.6km1.0km

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Inummary,hisnalysisndicateshatasednheallowableworstcase'MIL-STD-461levels,averyslightpoten-tialexistsforthedetectionofthe1401.52MHzLOemission.CaremustbetakentoassurethatthisunintentionalLOemissionisappropriatelyattenuatedbypropercableshielding,andthatsystemfilteringi.e.PSUEreceiveantennafiltering)lsoprovidesforadequateattenuation.Inamorepracticalsense,forreceiverswhichemitwellbelowtheallowedRE02level,detectionofthisemissioncouldbefeasibleonlyatveryshortranges,implyingthatthereisaverylowriskofInterceptibilitybasedonthisemission.

Table4.2summarizesinterceptreceiverrangerequirementsforeceptionfhenintentional50.38HzOmission.Equation( 6 )indicatesthatthepotentialEIRPofthe350.38MHzLOmayneverexceed-95.77dBW.asedonthispotentialpowerlevel,interceptcouldtakeplaceatrangesuptoapproximately2.1km.otethatatthisfrequency,lineofsight'snotrequiredfordetection.

Equation( 5 )indicatesthatthepowerlevelontheGPSUEIFcableisapproximately0dBm(-30dBW) .ssuminganIFcableradiatedpowershieldingattenuationof80dB,thepotentialEIRPofthe350.38MHzsignalcouldbeapproximately-110dBWimplyingthathighprobabilitydetectioncouldnotoccuratrangesgreaterthan. 5km.

Table4.3summarizesinterceptreceiverrangerequirementsforthepotentialunintentional10.23MHzemission.Aspreviouslydiscussed,thissignalhasthepotentialtoberichinoddandevenorderharmonics.fitisassumedthattheharmonicsmayradiateatthesamespecifiedEIRPlevelstheundamentalfrequency,thanobviouslydetectionrangeswillbeappropriatelyincreased.

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InconversationswithagenciesresponsibleforperformingEMI/EMCtestingoftheGPSUE(i.e.NADC,GTRI) ,thasbeenreportedthattheGPSUEhasbeenfoundtoadverselyaffectothercommunicationsystemslocatedonthesameplatformatintervalsof10.23MHzintheHF,UHF,and VHFregions.lthoughthisdoesnotexplicitlyimplythathighfar-fieldradiationlevelsexistatmultiplesof10.23MHz,withtheabsenceofanyfar-fieldmeasuredata,hesectualar-fieldevelsreurrentlyunknown.

ThesimplelinkanalysisformulapresentedinEquation( 8 )doesnottakeintoaccounttheeffectsofHFpropagationphenome-nasuchasionosphericreflection.iththisinmind,tisnotedinTable4.3thatdetectioncannottakeplaceatrangesgreaterthan m.herefore,asedonthisnalysis,heprobabilityofInterceptofthe10.23MHzLOanditsharmonicsislow.

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5.0 CONCLUSIONSConversationswithRockwell/Collinsengineershaveindicated

thattheactualemissionlevelsoftheGPSUEfallwellbelowtheallowableMIL-STD-461specification.elephonereferenceshavebeenmaderegardingthefollowingRockwell/Collinsreports:)EMIestReportforGPSRCVR3A,)MITestReportorGPSRCVR3S,and3 )AE-4EMITestReport.

Unfortunately,thesereportscouldnotbeobtainedintimetobereviewedanddiscussedinthecurrentdocument.heywillbeeviewedheneceivedteorgiaech.romxtensiveinteractionswithRockwell-Collinspersonnelitisnotexpectedthatheywillesultn ifferenterspectiveromhatpresentedhere.

Assupportedbythecalculationspresentedinthisreport,thepotentialforinterceptibilityoftheGPSUEisverylow.Itshouldeointeduthatar-fieldeasurementsereotperformedsartfheoutineockwell/Collinsestingprocedures.helinkcalculationspresentedinthisreportarebasedonapproximatenear-fieldtofar-fieldworstcasetransla-tions.

Eventhoughidealpropagationconditionsareimplicitinthesecalculations,theresultsdonotindicatedetectibilitiesofgreatconcern.nconsiderationoftheadditionalfactsthatthecalculationsarebasedonthemaximumallowableradiatedsignals(accordingtoemissionspecifications)andtheemissionsarereportedtobewellbelowspec,thereislittlereasonformajoroncernelativetothenterceptibilityofunintendedemissionsfromtheGPSreceiver.

Fromapracticalstandpoint,standardemissionsfromship-basedlatformshouldeadomuchhigherprobabilitiesfdetectibilityhannintentionalmissionsromhePSE.

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Figure5. 1illustratesacomparisonof'broadband'RE02levelsversusthespecifiedEMCON(EMissionCONtrol)levelat1nauticalmile.sshown,ear-fieldRE02evelsmeasuredat1meter)extrapolatedoutto1nauticalmilefallwellbelowtheEMCONlevel.

Iflannedndn-goingMC/EMIestsesultnieldstrengthshigherthanthoseexpected,itmaybenecessarytore-evaluatethesituationrelativetoInterceptibility.urrently,however,healculationsndiscussionsresentednhisreportndicatehatherobabilityfnterceptsow.Accordingly,ar-fieldmeasurementsofInterceptibilityarenotrecommended.

REFERENCES[ 1 ] Feher,Kamilo;DigitalCommunications.Satellite/EarthStationEngineering,PrenticeHall,1983.

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Documents

GPS Interceptibility Post-Test Analysis