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首页 A-GPS_OTA_WhitePaper

A-GPS_OTA_WhitePaper.pdf

A-GPS_OTA_WhitePaper

浪淘沙
2014-03-26 0人阅读 举报 0 0 暂无简介

简介:本文档为《A-GPS_OTA_WhitePaperpdf》,可适用于人文社科领域

WhitePaperAGPSOverTheAirTestMethod:BusinessandTechnologyImplicationsRonBorsato,SpirentCommunicationsDrMichaelDFoegelle,ETSLindgrenwwwspirentcomwwwspirentcomWiththeriseinLocationBasedServices(LBS)applicationsandtheneedtomeetErequirements,thenumberofmobilecellulardevicessupportingAssistedGPS(AGPS)issteadilygrowingAsoneoftheenablingLBStechnologies,AGPSofferscustomershigherpositionaccuracy,quickerlocationfixes,andimprovedcoverageofserviceindifficultlocations,suchasurbanandinbuildingenvironmentsAsaresult,mobileoperatorsanddevicemanufacturesarelookingfortestingchoicesthatquantifyandbenchmarkrealworlddeviceperformanceUntilrecently,allindustrydefinedAGPStestmethodologiesfocusedontestingtheperformanceofadeviceoveracabledRFconnection,bypassingtheGPSantennaandassociatedcircuitry,asshowninFigureThisapproachdoesnotgivethecompletepictureofrealworlddeviceperformanceanditsimpactontheenduserexperienceofLBSapplicationsToachievethis,GPSperformancetestingneedstoincludeallrelevantcomponentsAnOverTheAir(OTA)testmethodology,showninFigure,isthebestsolutiontoaddressthisneedThiswhitepaperpresentsanoverviewofthebusinessandtechnologydriversforOTAAGPStesting,whichdescribesamethodtosatisfytheradiatedtestingrequirementsofallinvolvedpartiesWhilethewhitepaperisintendedforDepartmentManagers,LabandRDManagers,andEngineersalreadyworkingwithAGPSorOTA,theintroductorycontentinthefollowingsectionsisalsobeneficialforthoseunfamiliarwiththeseconceptsIntroductionFigureConductedRFSignalFigureOverTheAirRFSignalwwwspirentcomConventionalStandaloneGPSWithconventionalstandaloneGPS,theGPSreceiverinthemobiledeviceissolelyresponsibleforreceivingsatellitesignalsandcomputingitslocationThismethodrequiresthedevicetotrackatleastfoursatellitestocomputeitslocationThesamemethodisusedbynearlyallPersonalNavigationDevices(PNDs)AnyonewhohasusedthesedeviceshasexperiencedthelongtimedelayassociatedwithgettingapositionfixwhenthedeviceisfirstpoweredonPNDsalsohavelimitationsinobtainingapositionfixinchallengingenvironments,suchasindoors,in“urbancanyons”,andunderdensefoliageFigureGPSUserinUrbanEnvironmentConventionalStandaloneGPSvsAssistedGPSAssistedGPSUsingwirelessconnectivity,mobiledevicescanalsosupportassistedGPS(AGPS)AGPSimprovesthelocationdeterminationperformancebyobtaining“assistance”datafromthenetworkoverthewirelesscommunicationchannel,enabling:•Fasterinitialacquisitionofsatellites•AneffectiveincreaseinGPSsensitivity,whichcanresultinpositionfixesinmorechallengingenvironments•Somepositioncalculationstobeoffloadedtoaremoteserver,freeingthedevice’sprocessortoservicemorecriticalfunctionsTheseadvantagesarethereasonnearlyallmobiledeviceswithGPSchipsetssupportAGPSMobiledevicescanmakeuseofseveraldifferentapproachestodeterminetheircurrentlocationSomeofthese–CellIdentification,UplinkTimeDifferenceofArrival(UTDOA),AdvancedForwardLinkTrilateration(AFLT),andEnhancedObservedTimeDifference(EOTD)–relyonthecellularnetworkAnotherpopularmethod,usedbydevicesthatsupportWirelessLAN(WLAN),ismappingknownWLANaccesspointsthenusingthisinformationtoapproximateadevice’scurrentlocationHowever,sincethemajorityoftheseapproacheshavelimitations,includingaccuracyandavailability,themostcommonmethodemployedinmobiledevicestodayistheGlobalPositioningSystem(GPS)GPSisaGlobalNavigationSatelliteSystemthathasbeenfullyoperationalsinceDeviceswithembeddedGPSreceivingcapabilityareabletoaccuratelycomputetheircurrentpositionalmostanywhereonearthwheresatellitesignalscanbereceivedThereliability,accuracy,andavailabilityofthistechnologyhavedrivenwidespreadadoptionMobiledeviceswithGPShavetwooptionswhendeterminingtheircurrentlocation:)ConventionalstandaloneGPScapabilitiesand)AssistedGPS(AGPS)wwwspirentcomRecently,industryorganizations,includingCTIA,haverecognizedtheneedtocreatestandardizedtestproceduresforAGPSOTAtestingtoobjectivelyspecifyandvalidateacceptableperformanceAsubgroupoftheCTIAorganizationhascompletedworktoincludeforthefirsttime,asectiononAGPSOTAtestingThisisincorporatedintheversionreleaseoftheCTIATestPlanforMobileStationOverTheAirPerformance(hereafterreferredtoastheCTIAOTATestPlan)ThegeneraltestmethodologydefinedinthisspecificationisexplainedinthefollowingsectionsofthiswhitepaperThecertificationorganizationforGlobalSystemforMobileCommunications(GSM)andUniversalMobileTelecommunicationsSystem(UMTS)devicessoldintoNorthAmerica,thePCSTypeCertificationReviewBoard(PTCRB),arelikelyadoptersofthenewversionoftheCTIAOTATestPlanItisalsolikelythatotherindustrybodieswilladoptsimilarmethodsinthefutureIndustryorganizationsarenottheonlyonesinterestedinmandatingAGPSOTArequirementsManynetworkoperatorsalsobelievethistestingisveryimportantandsomealreadyhaveAGPSOTAtestprogramsinplaceNowthatversionoftheCTIAOTATestPlanisfinalized,manyofthesenetworkoperatorsareexpectedtoadoptthemethodologyinthisspecificationtohelpensuretheperformanceoftheAGPScapabledevicestheyoffertheircustomersAboutCTIATheWirelessAssociationCTIATheWirelessAssociationisanindustryconsortiumrepresentingthewirelesscommunicationsindustryintheUnitedStatesFoundedin,thisorganizationrepresentsnetworkoperators,devicemanufacturers,wirelessdatanetworkingcompanies,andothercontributorstothewirelesssectorInadditiontolobbyingtheUSCongressandFCConbehalfofthewirelessindustryandoperatingoneoftheindustry’slargesttradeshows,CTIAmaintainsawirelessdevicecertificationprogramintendedtoensureahighstandardofqualityperformanceforconsumersOverTheAirTestingTheneedforOTAperformancetestingofcellularandWiFiwirelessdeviceshaslongbeenakeyrequirementintheoveralltestingprocessOvertheyears,standardOTAperformancetestplanshavebeencreatedbyorganizationssuchasCTIATheWirelessAssociation®,GPP,andWiFiAlliance®OTAtestingisperformedinacontrolledradiatedenvironment,calledananechoicchamber,usingspecializedequipmenttoprovideaknownsignaltothedeviceundertestAkeyaspectofthistestingisthatallsignalsaretransmittedandreceivedwirelessly,astheyareintherealworldThisensuresthatallinteractionfactorsbetweentheradioandtherestofthewirelessplatform,includingradiationpatternandplatforminterference,aretakenintoaccountwhendeterminingoverallwirelessperformanceUntilrecently,allAGPStestingtoindustrystandardswasperformedusingacabledRFconnectionAsaconsequence,devicesthatpassalltestsintheexistingconformancestandardsmayperformpoorlyintherealworldThisresultsinaninferiorenduserexperienceofLBSapplicationsandhasledsomeindustryleaderstocreatetheirownAGPSOTAsolutionswwwspirentcomThissectiongivesanoverviewoftheAGPSOTAtestmethodspecifiedintheversionreleaseoftheCTIAOTATestPlanAGPSOverTheAirtestingrequiresspecializedequipmentbeyondthatrequiredforconductedtestingoveranRFcableThetestmethoddescribedinthissectionappliestoUMTS,GSM,andCodeDivisionMultipleAccess(CDMA)devicesRequiredEquipmentandSetupThegoalofOTAtestingistoobtaina“snapshot”oftheperformanceofthedeviceundertest(DUT)inalldirectionsaroundthedeviceForexample,considerarequirementtocomparetheamountoflightemittedfromalightbulbaroundtheroominalldirectionsItisnecessarytolookatthelightbulbfromalldirectionstomeasureandcomparetheresultsTheDUTisconfiguredfortypicalusecasesForamobiledevice,thisincludesuseofaphantomheadandhandtosimulatetheeffectsofadeviceheldagainstthehumanheadForhandheldapplications,suchaspersonalnavigationusingAGPS,aphantomhandisusedtoholdthedeviceinthesamewayausertypicallywouldThus,theRFshadowsandnearfieldeffectscausedbytheproximitytothesephantomscanbetakenintoaccountwhendeterminingthedeviceperformanceTheradiatedenergyfromortotheDUTismeasuredbyplacingaMeasurementAntenna(MA)afixeddistanceawayfromthedeviceBecausetheDUTcanberandomlyorientedwithrespecttotheMA,adualpolarizedmeasurementantennaisusedtomeasuretwoorthogonalpolarizationsrecordingthetotalradiatedenergyirrespectiveoftherelativeorientationInalllikelihood,thedevicewillbeoperatinginahighlyscatteredenvironmentwhenoperatingnearthelimitofitssensitivityInthiscase,thedevicedoesnotfavoranyparticularpolarizationThetestmethodologyforAGPSOTAtestingutilizesanMAwithlinearpolarization,asopposedtocircularpolarizationtoremaincompatiblewiththeexistingCTIAOTATestPlanTocoverallpointsonthesurfaceofaspheresurroundingthedevice,itisnecessarytobeabletomovetheMArelativetotheDUTintwoorthogonalaxesImaginelookingataglobeoftheEarthandwantingtoensurethatyouhaveobservedeverypartofitssurfaceequallyYouwouldhavetomovenorthandsouth,aswellaseastandwest,tocovertheentireglobeThisAGPSOverTheAirTestMethodmovementoftheMArelativetotheDUTrequiressomeformofsphericalpositioningsystemTherearetwocommonwaystoachievethisThefirstistomounttwoorthogonalpositioners,oneontopoftheother,torotatetheDUTintwoaxesInthiscombinedaxisscenario,theMAremainsfixed,whiletheDUTrotatesintwoaxesThesecondinvolvesplacingtheDUTonaturntableandusingaseparatepositionertomovetheMAupanddownarounditIneithercase,fromtheviewpointoftheDUT,theMAmovesnorthsouth(theta(q)axis)andeastwest(phi(f)axis)aroundit,resultinginfullsphericalcoverageToavoidunwantedinterferencefromoutsidesignalsources,andpreventinterferencewithothercommunicationsystems,theDUTandMAmustbeshieldedfromtheoutsideworldThisisdonebyplacingtheminsideanRFshieldedroomHowever,whiletheshieldreflectsexternalenergyawayfromtheDUT,italsoreflectsenergyradiatedfromtheDUTbacktowardstheMAandviceversaThiscanresultintheenergybeingmeasuredmorethanonceThisduplicationoccursbecausetheenergycanbemeasureddirectlyfromtheDUT,aswellasafteritreflectsoffthewallsoftheroomTopreventthisfromhappening,theroommustbelinedwithRFabsorbingmaterialtoreduceunwantedreflectionsTheresultisafullyanechoicchamberwhereallofthewalls,thefloor,andtheceilingarelinedwithRFabsorberOutsidethechamber,themeasurementantennamustbeconnectedtotestinstrumentationtomeasurethepowerradiatedfromtheDUT,ortotransmitsignalsataknownleveltotheDUTtodetermineitsreceiversensitivityThepathlossassociatedwithcabling,measurementantennagain,andrangepathlossmustbeappliedtocorrectthetestequipmentreadingtocorrespondtowhatisoccurringattheDUTTodetermineradiatedpowerfromtheDUT,asignalanalyzerorpowermeteristypicallyusedTodeterminethereceiversensitivityoftheDUT,aNetworkEmulator(NE),orsatellitesimulatorinthecaseofAGPStesting,providestheknowndownlinksignalwwwspirentcomDependingonwhattestinstrumentmustbeconnectedtotheMA,itisoftennotpracticaltomaintainthecommunicationlinktotheDUTthroughtheMAThus,aseparatecommunicationantennaistypicallyusedtoprovideadedicatedcommunicationpathbetweentheNEandDUTThiscanprovidealowlossuplinkpathwhentheMAisusedfordownlinkonlytestsItcanalsoprovidebidirectionalcommunicationsignalingwhentheMAisconnectedtoasignalanalyzerforpowermeasurementBecausemostcommunicationtestequipmentisdesignedforconductedtesting,additionalsignalconditioningcomponentsareusuallyrequiredtoadapttheOverTheAirsignalstotheavailabledynamicrangeoftheinstrumentationAnRFswitchmatrixisusedtoprovideallofthenecessaryroutingbetweenthecomponentpartsofthesystemFinally,aPCrunningtestautomationsoftwareisusedtocontrolthepositioningsystemandcapturethedesiredmeasurementsfromallorientationsaroundtheDUTFigureillustratesatypicaltestsysteminwhichtheDUTisrotatedintwoaxesandwhichiscapableofperformingOTAtestingforanumberoftechnologiesTestProcedureandInterpretationofResultsBecausetheGPSradioisreceiveonly,themaininterestisinevaluatingreceiversensitivityfromvariousdirectionsaroundthedeviceTheresultingEffectiveIsotropicSensitivity(EIS)patternthendeterminestheaverageradiatedreceiversensitivityacrosstheentirespherearoundthedevice,referredtoasTotalIsotropicSensitivity(TIS),oracrossaportionofthesphereInadditiontodeterminingthebaselineradiatedsensitivityoftheGPSreceiver,theeffectofcellularcommunicationontheGPSreceiverisevaluatedtoensurethattheGPSreceiverperformanceisnotdegradedduetointerferencefromthemobilephonetransmitterTraditionally,aTISmeasurement(themeasurementofanEISpattern)isdeterminedbyperformingasensitivitysearchateachpointaroundthedeviceThesignalleveltransmittedtothedeviceislowereduntilatargeterrorrateisreportedbythedeviceThatdefinesthelimitofthedevice’sreceiversensitivityforthatdirectionTheresultisacontouredradiationpatternwherethepeaksrepresentsintheantennapatternwheremorepowerwasrequiredtogetthesignalthrough,andthevalleyscorrespondtothepeaksintheantennapatternwherethedeviceisthemostsensitiveAGPSOvertheAirTestMethod(cont’d)FigureTypicalOTAEquipmentSetup(DiagramusedwithpermissionofETSLindgren)DUTMultiAxisPositionerDualPolarizedMeasurementAntennaFullyAnechoicChamberRFAbsorberMaterialCommunicationAntennaMeasurementSignalPathCommunicationSignalPathBaseStationEmulatorDynamicRangeSignalConditioningRFSwitchMatrixBroadbandSignalAnalyzerPositioningControllerSatelliteSimulatorPCRunningTestAutomationSoftwareFiberOpticControlLinesNetworkEmulatorwwwspirentcomDeterminationoftheTISforanAGPSdeviceiscomplicatedbythetimeinvolvedindetermininga“good”vs“bad”resultAsingleAGPSfixcantakeoverseconds,andrepeatedfixesarerequiredasthepowerisloweredItisalsorequiredtoobtainalevelofstatisticalconfidencethattheappropriatesensitivitylevelhasbeendeterminedTodothisfromalldirectionsaroundadevicecouldeasilyrequiredaysoftestingAsanalternative,amethodhasbeendevelopedtotakemeasurementsfromtheAGPSdeviceitselftohelpdeterminetheradiationpatternofthedeviceTheresultantpatternisthennormalizedtoasingleEISsensitivitysearchtodetermineanestimatefortheentireEISpatternThetestprocedureconsistsoffivesteps:AntennapatternLinearizationRadiatedsensitivityTIS,UHIS,andPIGScalculationIntermediatechanneldegradationInadditiontounderstandingthetestmethodforAGPSOTA,itisimportanttounderstandthesignificanceofeachmeasurementandhowitisusedtoquantifytheAGPSperformanceofdevicesThisallowsdevicemanufacturerstocreatebetterperformingdevicesandhelpsnetworkoperatorsensurethatdeviceslaunchedontheirnetworkperformwellAntennaPatternThefirstpartoftheAGPSOTATestPlancallsformeasurementoftheGPSantennapatternAnantennapatterncanberepresentedvisuallytoidentifythewirelessdevice’sabilitytoeffectivelyreceivesignalsfromdifferentdirectionsImaginetheantennaatthecenteroftheshapeinFiguretheareaswithlargepeakssignifythedirectionsfromwhichtheantennareceivessignalsmosteffectivelyFigureTypicalGPSAntennaPatternAntennapatternmeasurementisimportantinquantifyingthetrueperformanceofGPSantennasinmobiledevicesAsdevicesbecomesmaller,morepowerful,andpricedlower,thetradeoffsbetweensize,cost,andperformancebecomemoredifficultThisisalsotruefortheGPSantennasnowembeddedinnearlyallhighendmobiledevices,andanincreasingnumberofmidandlowenddevicesForthesedevicestodeliveragooduserexperienceforlocationbasedapplications,theGPSantennapatternshouldbecompromisedaslittleaspossibleTheantennapatternofadevicecanbeimpactedbyanumberoffactorsincluding,butnotlimitedto:•GPSantennadesign•Deviceformfactor•LocationoftheGPSantennainthedevice•PresenceofahumanheadorhandnearthedevicewwwspirentcomFigureillustratestheimpactofahumanheadonaGPSantennapatternNotethelargevalleyatthelocationoftheheadFigureImpactofHumanHeadonAntennaPatternFigurestressestheimportanceofGPSantennalocationInthiscase,theantennaisatthebottomofthedevice(noticethepeaksfacingdownwards)whenthedeviceishelduprightSincethedeviceclearlyfailstoeffectivelyreceiveGPSsignalsfromdirectlyoverhead,itislikelytobearelativelypoorperformerFigurePoorlyPerformingAntennaPatternWhileit’snotuncommontoperformpassiveteststoevaluateanantennaradiationpatternbyfeedingitwithanRFcable,thisisavoidedforOTAtestingforseveralreasonsTheRFcableitselfcandrasticallychangetheradiationpatternofadevice,especiallyforelectricallysmalldeviceslikeatypicalmobilephoneInaddition,theresultsfrominteractionsbetweentheradio,antenna,anddeviceplatformarenotthesameastheperformanceoftheindividualsystemcomponentsForAGPSOTAtesting,theantennapatternisestablishedbyradiatingaknownGPSsignalpowerlevelandobtainingfullsphericalcoveragearoundthedeviceBykeepingtrackoftheGPSpowerlevelsthattheDUTmeasures,itispossibletoplothowwellthedevicereceivesGPSsignalsatdifferentanglesofarrivalForAGPS,themetricusedtocharacterizetheantennapatternisthecarriertonoiseratio(CN)oftheGPSsignalFortheCTIAdefinedtests,discretepositionsarerequiredforfullsphericalcoverageMeasurementsaremadeintwoaxes(fiveanglesinthetheta

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