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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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X2
So
i.= 3 +J Oa ; + -> o
in coo
< _ > oa:iCO i-3CD
I2 X2to1^ C M C D II in
I
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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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