Building Blocks for Small Aircraft APNT · building blocks for small aircraft APNT (Months: 3-10) of NAVISAS. It provides an overview of the state of the art of navigation techniques

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Building Blocks for SmallAircraftAPNT

D3.1 NAVISAS Grant: 699387 Call: H2020-SESAR-2015-1

Topic: Sesar-08-2015 Communication, Navigation andSurveillance(CNS) Consortiumcoordinator: TEKEVERASDS Editiondate: 15June2017 Edition: 00.02.00

EXPLORATORYRESEARCHRef. Ares(2017)3028540 - 16/06/2017

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©-2016–NAVISASConsortium.Allrightsreserved.

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Authoring&Approval

AuthorsofthedocumentName/Beneficiary Position/Title Date

TEKEVERASDS Coordinator 04/01/2017

CSEM Partner,WP3Leader 04/01/2017

SHARK.AERO Partner 04/01/2017

THALESAVIONICS Partner 04/01/2017

ReviewersinternaltotheprojectName/Beneficiary Position/Title Date

RicardoMendes/TEKEVERASDS COO 05/01/2017

AndréOliveira/TEKEVERASDS BusinessDevelopmentManager 06/01/2017

ApprovedforsubmissiontotheSJUBy—RepresentativesofbeneficiariesinvolvedintheprojectName/Beneficiary Position/Title Date

AndréOliveira/TEKEVERASDS BusinessDevelopmentManager 06/01/2017

RejectedBy-RepresentativesofbeneficiariesinvolvedintheprojectName/Beneficiary Position/Title Date

DocumentHistory

Edition Date Status Author Justification

00.00.01 06/11/2016 Firstcontentinput TEKEVERASDS

00.00.02 26/11/2016 IntegrationofcontentCSEM

00.00.03 07/12/2016 IntegrationofcontentSHARK.AERO

00.00.04 12/12/2016 IntegrationofcontentTEKEVERASDS

00.00.05 04/01/2017 IntegrationofcontentTHALESAVIONICS

00.00.06 05/01/2017 Finalharmonization AndréOliveira

00.01.00 06/01/2017 Issued AndréOliveira

PROJECTMANAGEMENTPLAN

©-2016–NAVISASConsortium.Allrightsreserved. 3

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00.02.00 15/06/2017 Secondissue AndréOliveira AddressingremarksofSESARJU

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NAVISASNAVIGATIONOFAIRBORNEVEHICLEWITHINTEGRATEDSPACEANDATOMICSIGNALS

ThisprojecthasreceivedfundingfromtheSingleEuropeanSkyATM(AirTrafficManagement)ResearchJointUndertakingundergrantagreementNo699387.

Abstract

ThisdocumentcomprisestheworkperformedunderWP3-State-of-the-artandanalysisofbuildingblocksforsmallaircraftAPNT(Months:3-10)ofNAVISAS.Itprovidesanoverviewofthestateoftheartofnavigationtechniques(includingthoseapplicabletosmallaircraft)andananalysisofthestateoftheartforatomicclocksandatomicgyros.Furthermore,itreportsontheexperimentscarriedouttoverifythattheNAVISASatomicgyroandatomicclockareinlinewiththecurrentstateoftheart.Atthisstageoftheproject,theconsortiumhasbeenableto achieve TRL2.5. Finally, the document proposes an operational concept for the use ofNAVISASbysmallaircraft.



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ExecutiveSummary

TheobjectivesofthedeliverableD3.1aretoreportupontheworkcarriedoutunderWP3“State-of-the-artandanalysisofbuildingblocksforsmallaircraftAPNT”[Months:3-10]whichhasthefollowingobjectives:

- Toclearlydefinethestate-of-the-artinnavigationtechniques,clocksandatomicgyrosatthetimeofprojectexecutionandinthelightoflatestSESARdevelopments.

- Toclarifythestate-of-the-artonatomicgyrosandclocksthroughexperiments.

- TocreateapoolofbuildingblocksthatareinlinewithWP2requirementsandwillserveasthesolutionworkspacesubsetthatwillbeusedinWP4fortheconceptdesign.

Concerningthefirstsetofactivities,theconsortiumanalysedseveralnavigationtechniquesincludingthefollowing:

• GlobalNavigationSatelliteSystem(GNSS)• SpaceBasedAugmentationSystem(SBAS)• GroundBasedAugmentationSystem(GBAS)• CombinationofGNSSwithInertialNavigationSystems(INS)• CombinationofINSwithradar• CombinationofINSwithimagery• Beaconbasednavigation

o NonDirectionalBeacons(NDB)o VHFOmnidirectionalRadiorange(VOR)o DistanceMeasuringEquipment(DME)

• SignalsofOpportunity(SoOP)basedono ReceivedSignalStrength(RSS)o AngleofArrival(AOA)o TimeDifferenceofArrival(TDOA)o Pseudorangemeasurement

Notallofthetechniquesmentionedaboveapplytosmallaircraft.Theyhaveincludedintheanalysisnonethelessforcompleteness.Foralltechniques,theconsortiumdescribedtheprincipleofoperation,assessedthematurityofthetechnique(e.g.whilebeaconbasednavigationisstateofplay,SBASis

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stateoftheartandSoOPisstillininfantresearchphases),identifiedtheequipageandinfrastructureneedsanddescribedtheperformancesachievable.

Relevantresearchactivitiesinthesedomainshavealsobeenidentifiedandreferenced.

The consortium concluded themajority of small aircraft (GA,VLA,UL andUAVs as definedby theproject)relyonGNSSandthecombinationofGNSSwithINSfornavigation.MannedsmallaircrafttendtorelyonGNSSreceiversandmakeuseofbeaconbasednavigationmostlyforinstructionalpurposes.ThevastmajorityofunmannedaircraftrelypurelyonGNSSoronthecombinationofGNSSwithINSorothersensors(suchasradioaltimetersorimagery)tonavigateandperformautomaticapproachesand landings.ThecombinationofGNSSwith imagery isbeingexploitedmostlybyverysmallUAVsflyingindoors(outdoorflighttendstousethemoreversatileGNSS).SomesmallA/CalsomakeuseofSBASbuttoamuchsmallerextent.

GBASisalmostsolelyusedbycommercialaircraftwhileSoOPtechniquesarenotmatureenoughatthemomentforregularuseinaerialnavigation.

Concerning the state of the art analysis of atomic clocks (MAC) and atomic gyros (Spin NuclearMagnetic Resonance or SNMR), the consortium explained the principles of operation for eachtechnologyandperformedpatentsurveysonbothtechnologies.Commercialproductsonthemarketwere identified and assessed. In order tomake aMAC competitive, the performance in terms offrequencystabilityisessentialbuttheformfactorandthecostsareofkeyimportanceaswell.Thephysicspackageisacriticalelementneededtofulfillthesechallengesandsofarnosolutionexiststhatishighperformingandcompetitiveincost.Themainaspectsofthephysicspackageareitsformfactor,powerconsumptionandproductioncost.

ThepatentsurveyonMAChasdemonstratedapeakinpatentapplicationsinthisareaaround2010(coincident with major DARPA work funding). The main players in the domain are Honeywell,MicrosemiandNorthropGrumman.AlthoughSeiko/Epsonisthetoprankingpatentapplicant, theyhaveneitheracorrespondingproductnorascientificdemonstratorofaMAC.Thehighnumberofpatentsisinpartduetoahighnumberofpatentfamilieswithonlyminordifferencesinthecontainedclaims.

TheconsortiumthenexplainedtheapproachesusedbydifferentgroupstorealizeMACprototypes.Prototypepackagesdevelopedbythefollowinggroupshavebeenconsideredandpresented:

- WestinghouseandNorthropGrumman- NationalInstituteforStandardsandTechnology(NIST)- Microsemi/Symmetricom/DraperLaboratory/SandiaNationalLabs- TeledyneScientific/RockwellCollins/AgilentTechnologies- Honeywell- Sarnoff/Princeton/FrequencyElectronics- MAC-TFCconsortiumandISIMACconsortium- SpectratimeOrolia- CSEM

Withrespecttotheatomicgyrosstateoftheart,theconsortiumanalysedandexplainedthemaintechnicalaspectsbehindtheoperationanddesignofthesedevices.Theseinclude:



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- Polarization,achievedthroughopticalpumping(threedifferenttechniquesarecurrentlyused);

- Precession–applyinganoscillatingfieldtoinducecoherence;- Detectionoftheprecessingnuclearmagnetization,achievedthroughopticaldetectionbased

ondifferenttechniqueso Dehmelttechniqueo Faradayrotationo Inductioncoilso Externalmagnetometers

BenchmarkingofNMRgyrosbasedonavailablepublic informationwascarriedout (theresultsaresummarizedbelow).Afterwards, theconsortium identified themaindifferences in termsofdesignbetweentheNAVISASgyroandNorthropGrumman’s.Finally,thepossiblesharedblocksbetweentheSNMRgyroandtheMACforNAVISASwereidentified:

• SametechnologytofabricateMEMScell• Pump/probelaser• Cellheating• Useoftheclockcelltostabilizepumplaserforgyro• SharingofRFmodulationoflaserfor(i)CPT(coherentpopulationtrapping)interrogationof

clockand(ii)dual–frequencypumpingofgyro• Sharingofpartsofmagneticshielding

InordertoprepareandsupporttheER/IRgateattheendoftheproject,aTRLroadmapwasdevelopedandTRLmilestoneswereintroducedintheprojectGanttchartintheProjectManagementPlan(PMP).Duringthisreportingperiod,theconsortiumhasmanagedtoachieveTRL2+throughthesuccessfulofthefirstthreestepsoftheTRLroadmap,asrepresentedinthetablebelow.TheconsortiumcarriedoutteststoverifytheTRLoftheNAVISASgyroconcept.Theexperimentalsetupandactualtestscarriedoutaswellastheirresultsarepresented.Someresultsoflaboratorytestsperformedtomeasurekeyparametersofinterestforthetechnologiesofinterestwereobtainedandthepartnersbelievethesecan validate some of the assumptions of the previous maturity level concerning aspects likeperformance.

ThefinalactivityofWP3wastask3.4dedicatedtothecreationofapoolofbuildingblocksinlinewithWP2requirementsthatcanserveasthesubsetofthesolutionworkspaceforWP4andthebeginningofthedefinitionoftheoverallsystematconceptual level.Afterinternaldiscussion,theconsortiumconcluded thatat thecurrent stageofdevelopmentof theproject (whichhas fulfilled its foreseenobjectives) and given that a blockdiagramexplaining thedifferent blocks ofNAVISASwas alreadyproposedinWP2(refertoFigure41elsewhereinthisdocument)itwouldnotmakesensetocarryouttheseactivitiesastheteamwouldberepeatingworkfromWP2andunabletoprogressmoreonthedetailingoftheblocks.Alternatively,itwasagreedthatNAVISASwasmissinganoperationalconceptfor small A/C. Therefore, the consortium agreed to pursue the development of one or moreoperationalconceptsthatexplainhowtheconsortiumenvisagestheusageofNAVISASbythesmall

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A/Cuniverse.TheideabehindthisisfortheoperationalconceptstoprovideabiggerpictureonwhatvalueNAVISAScanbring to small aircraft andhelpunderstandwhat is achievableandunderwhatconditions. After this analysis is completed it will be possible to progress on the building blocksdetailingworkthatwasinitiallyplannedforWP3.4.

Thediscussionsbetweenpartnershaveyieldedthefollowingpotentialoperationalconceptsbasedontheassumptionthatbaselinenavigationinsmallaircraft(GA,VLA,ULandUAVs)isperformedbyusingacombinationofINSandGNSS:

- NAVISASMACcanbeusedtodetectGNSSspoofing-Thiscaseisapplicableinallflightphases,allflightrules(IFRandVFR)andrelevantforbothmannedandunmannedsmallaircraft;

- AnINScomprisingasetof3NAVISASGyroscombinedwithaccelerometersandaKalmanfiltercanbeusedtoprovidenavigationincaseswhereGNSSsignalsarelost

o UnderVFRconditions,NAVISAScanbeusedtoprovideconditionssimilartoIFRbutwithlessconstraints;

o UnderIFRconditionsandwhenflyingen-route,asmallaircraftcanrelyontheNAVISASbasedINSto“buytime”andcoastuntilGNSSsignalsarereacquired.Ifafterapre-determinedperiodGNSSisstillnotavailabletheA/Cwillhavetoreverttoanemergencyprocedure;

o UAVsmayusetheNAVISASgyrostocarryoutemergencyprocedures;o TheNAVISASbasedINSmaybeusedtoreacquireGNSSsignalsfaster;o ItmaybepossibletousetheNAVISASbasedINStostillgetGNSSsignalsunder

jammingconditions;

TheNAVISASsystemcomprisingtheGNSSplusMACplussetof3gyrosandaccelerometerscanbeusedtocarryoutauto-landoperationsforbothunmannedandmannedsmallaircraftaslongasanadditionalsensorisconsideredtoincreasetheverticalaccuracy(e.g.radioaltimetersorLIDAR).

Finally,asetofoperationalconceptsforhowNAVISAStechnologiescouldbeusedinRPASandGA/VLA is presented. The relationship between NAVISAS technological blocks and the SESAR ATMmasterplan is established and a possible roadmap for developing an A-PNT based on NAVISAStechnologyispresented.



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TableofContents

Abstract.......................................................................................................................................4

ExecutiveSummary............................................................................................................5

TableofContents...............................................................................................................9

ListofTables....................................................................................................................11

ListofFigures...................................................................................................................12

ListofAcronyms...............................................................................................................15

Introduction..............................................................................................................17

ScopeandStructureofthedocument........................................................................................17

StateoftheArtinnavigation....................................................................................19

2.1 Beaconbasedtechniques...............................................................................................19

2.2 GlobalNavigationSatelliteSystems(GNSS)....................................................................22

2.3 SpaceBasedAugmentationSystem(SBAS).....................................................................25

2.4 GroundBasedAugmentationSystem(GBAS)..................................................................28

2.5 InertialNavigationSystems(INS)....................................................................................30

2.6 GNSSplusINS.................................................................................................................32

2.7 INSplusRadar................................................................................................................342.8 INSplusimagery.............................................................................................................36

2.9 SignalsofOpportunity(SoOP)........................................................................................37

2.10 NavigationinGA,VLAandUltra-Lights...........................................................................40

2.11 NavigationinUAVsandDrones......................................................................................43

2.12 CompatibilitywithSESARconcepts................................................................................44

StateoftheArtreviewonclocksandatomicgyroscopes...........................................49

3.1 Miniatureatomicclocks.................................................................................................49

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3.2 Miniatureatomicgyroscopes.........................................................................................60

ExperimentstoclarifySoAoftechnologyonintegrationofclocksandatomicgyroscopes.......................................................................................................................77

4.1 RelationwithTRLmanagementplan..............................................................................77

4.2 Test1:MEMScellsfabricationandcharacterization.......................................................78

4.3 Test2:Experimentalsetup.............................................................................................81

4.4 Test3:Residualfieldsmeasurements.............................................................................85

OperationalGainsofaNAVISASbasedA-PNT...........................................................88

5.1 NAVISASOperationalConcepts......................................................................................88

5.2 MethodappliedtodefineNAVISASvisionsandoperationalconcepts............................91

5.3 NAVISASproposedtechnologies.....................................................................................91

5.4 Foreseenoperations.......................................................................................................92

5.5 WhatcanNAVISAScontribute........................................................................................94

5.6 NAVISASrelationtotheSESARATMMasterPlan...........................................................96

Conclusion...............................................................................................................103



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ListofTables

Table1–Acronymsandabbreviations.................................................................................................16

Table2:TasksofWP3...........................................................................................................................17

Table3:comparisonbetweensatellitenavigationandinertialnavigation..........................................33

Table4–SummaryofalternateA-PNTtechnologies............................................................................48

Table5:Comparisonofrelevantoscillatorsandclocks.ThelastcolumnalsopresentstheC-MACPPtargetspecifications......................................................................................................................52

Table6:Performancerequirementsfordifferentclassesofgyroscopes.............................................62

Table7-SummarytableofNMRGperformances................................................................................75

Table8–ListofteststosupportNAVISASTRLprogression..................................................................78

Table9–Outputpowercharacterizationofthecellheatingunit........................................................84

Table10–Residualfields......................................................................................................................87

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ListofFigures

Figure1-VOR/DMEbeacon..................................................................................................................21

Figure2-ComparisonbetweentheconstellationsofseveralGNSS....................................................23

Figure3-TypicalGeneralAviationgradereceiver(Garminaera796).................................................24

Figure4-TypicalUAVreceiver(u-bloxLEA-M8T).................................................................................25

Figure5-GlobalcoverageofseveralSBAS...........................................................................................27

Figure6-ArchitectureofGBAS.............................................................................................................29

Figure7-Twoexamplesof inertialplatforms.Left:abreakoutboardofthe InvensenseMPU-6050.Right:TheHoneywellHGU1930....................................................................................................32

Figure8-TheTrimbleAP20,aGNSS+Inertialplatformwhichcanbeusedforairborneapplications34

Figure9:LatestGarminG1000NXicockpit............................................................................................41

Figure10:GarminG1000architecturediagram....................................................................................43

Figure1.BlocdiagramofaMAC(i.e.apassiveatomicclock)..............................................................51

Figure2:Left:NumberofpatentapplicationsforyearrelatedtoMACs.Right:Top19patentassigneesfocusingonMACPPs(#patentsfamiliesrelatedtoMACPPsperassignee)................................53

Figure3:Westinghouse/NorthropGrummanPP................................................................................54

Figure4:NISTPP...................................................................................................................................54

Figure5:Microsemi/Symmetricon/DraperLab/SandiaNationalLabsPP.......................................55

Figure6:Teledyne/RockwellCollins/AgilentPP.................................................................................56

Figure7:HoneywellPP..........................................................................................................................57

Figure8:Sarnoff/Princeton/frequencyElectronicsPP.......................................................................58

Figure9:MAC-TFCPP............................................................................................................................58

Figure10:SpectratimePP.....................................................................................................................59

Figure11:CSEMPP...............................................................................................................................60



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Figure12:Gyroscopesusedfornavigationandtheirperformances...................................................63

Figure 13 – Left: ARWas a function of signal-noise ratio and relaxation time, Ref [39]. Right: biasinstabilityduetostraymagneticfieldsfordifferentnoblegasnuclei,Ref[39]...........................65

Figure14-PrincipleofoperationofanNMRgyroscope,Ref[39]........................................................66

Figure15-SchemeoftheLittongyroscope.FromRef[54]..................................................................70

Figure16-Gyrointernalstructure,physicspackageofthelatestversion...........................................72

Figure17-SchematicoftheNISTgyroscope.FromRef[58]................................................................74

Figure18-Schematicdiagramoftheworkingprincipleofthedifferentialmagnetometer................74

Figure19–NAVISASTRLroadmap........................................................................................................78

Figure20-DescriptionoftheMEMScells.Left:wafershowingcellswithdifferentdiameters.Middle-Right:Computersimulationsofamountedcell............................................................................79

Figure21–MEMScellsfabricationprocess..........................................................................................80

Figure22–Simulatedabsorptionspectrum.........................................................................................81

Figure23–Absorptionmeasurement..................................................................................................81

Figure24-Schematicsandpictureofthesetupwithclosedshielding................................................82

Figure25-a)Testsphericalcellwith3DprintedABS+resincellandferrulesmount.Toimproveheatingefficiency, black aluminium foil tape (Thorlabs AT205-1) is glued on the cell. b) MEMS cellmountedonmachinedTeflonholder,rotatingferruleholdersare3Dprintedwitharesin.c)18W,980nmdiode lasermountedonacoolingtower.d)Testsphericalcellmounted insidetheHemholtzcoilsandprobe-beammirrorssupportthatisslidinginsidetheshielding...................83

Figure26–Left:Sphericaltestcell,Right:4mmØMEMScell.............................................................84

Figure27–Testsphericalcellabsorptionspectra................................................................................85

Figure28–MagneticfieldsaxisdefinitionwithnT/mAscales.............................................................85

Figure29–Left:SignalmeasuredonPD1fordifferentpumppowers(probebeamremoved).Bzissweptat1Hz.Bx=0,50kHzRFoncoilY.Right:positionoftheRb87andRb85dipsasafunctionoftheBzfield...........................................................................................................................................86

Figure30-Left:SignalmeasuredonPD1fordifferentpumppowers(probebeamremoved).Bxissweptat1Hzaroundzero.Bz=By=0.Right:positionofthemaximaasafunctionoftheBxfield..........87

Figure41:PreliminaryNAVISASfunctionalblockdiagram(takenfromNAVISASD2.1).......................88

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ListofAcronyms

Acronym /Abbreviation

Meaning

AM AmplitudeModulationANSP AirNavigationServiceProviderAoA AngleofArrivalAPNT AlternativePositioning,NavigationandTimingATM AirTrafficManagementCNS Communication,NavigationandSurveillanceCS CertificationSpecificationsDF DirectionFinderDGNSS DifferentialGNSSDME DistanceMeasuringEquipmentEASA EuropeanAviationSafetyAgencyEGNOS EuropeanGeo-stationaryNavigationOverlaySystemELT EmergencyLocatorTransmitterEPIRB EmergencyPositionIndicatingRadiobeaconEVS EnhancedVisionSystemFAA FederalAviationAuthorityFMS FlightManagementSystemFOG FibreOpticGyroGA GeneralAviationGAGAN GPSAidedGEOAugmentedNavigationGBAS GroundBasedAugmentationSystemGLS GBASLandingSystemGNSS GlobalNavigationSatelliteSystemHEO HighlyEllipticalOrbitIAOPA InternationalcouncilofAircraftOwnerandPilotAssociationsICAO InternationalCivilAviationOrganizationIFALPA InternationalFederationofAirLinePilots’AssociationsIFR InstrumentFlightRulesIFR InstrumentFlightRulesILS InstrumentLandingSystemIMG IndustryManagementGroup

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IMU InertialMeasurementUnitINS InertialNavigationSystemION InstituteofNavigationLIDAR LightDistanceandRangingLORAN LongRangeNavigationMAC MiniatureAtomicClockMAG MiniatureAtomicGyroscopeMEMS MicroElectroMechanicalSystemsMEO MediumEarthOrbitNDB NonDirectionalBeaconPBN PerformanceBasedNavigationPP PhysicsPackageRAIM ReceiverAutonomousIntegrityMonitoringRLG RingLaserGyroRNAV AreaNavigationRNP RequiredNavigationPerformanceRPAS RemotelyPilotedAircraftSystemRSS ReceivedSignalStrengthSBAS SpaceBasedAugmentationSystemSNMR SpinNuclearMagneticResonanceSoOP SignalsofOpportunityTBD ToBeDeterminedTDoA TimeDifferenceofArrivalTRL TechnologyReadinessLevelUAS UnmannedAerialSystemUAV UnmannedAerialVehicleUL UltraLightVDB VHFDataBroadcastVFR VisualFlightRulesVFR VisualFlightRulesVLA VeryLightAircraftVOR VHFOmnidirectionalRangeVSG VibratingStructureGyroWAAS WideAreaAugmentationSystemWAM WideAreaMultilaterationWP WorkPackage

Table1–Acronymsandabbreviations.



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Introduction

WP3aimedtoestablishthestateoftheartintermsofnavigationtechniquesspecificallyforsmallA/Casdefinedby theprojectandcommercialaviation ingeneraland in the fieldofatomicclocksandatomicgyros.ItwasalsoitsobjectivetodefineandcarryoutanumberofexperimentsdesignedtoclarifythestateoftheartontheintegrationofatomicclocksandatomicgyrosandtoprogresstheTRLofbothtechnologies.Finally, itaimedtoanalyseandproposedescriptionsofthebuildingblocksofNAVISAStobeusedforthedevelopmentofaAPNTsystemforsmallaircraft.TheWPwasdividedintofourtasksasrepresentedbelowinTable2.

WP3Task

Title Leaders

T3.1 State-of-the-artinnavigation TEK,SHARK

T3.2 State-of-the-artreviewonclocksandatomicgyros CSEM

T3.3 Experiments to clarify state-of-the-art of technology on integration ofclocksandatomicgyroscopes

CSEM,TEK

T3.4 AnalysisofbuildingblocksforsmallaircraftAPNT TEK,TAV

Table2:TasksofWP3.

Thedocumentreportsontheworkcarriedoutunderthetasksaboveandprovidesdescriptionsandsummariesoftheanalysescarriedout.

ScopeandStructureofthedocument

ThescopeofthisdocumentistoclearlydefinethestateoftheartforthedomainsthataredirectlyrelatedtoNAVISASanditstechnologies, i.e.aircraftnavigationtechniquesandminiaturizedatomicclocksandminiaturizedatomicgyroscopes.Thestepstakenbytheconsortiumtoverifythetechnologyreadinessleveloftheproposedminiaturizedatomicgyroarealsodescribedandtheresultsobtainedbythelaboratoryexperimentsaregiven.Finally,afteridentifyingagapconcerningthepossibleusage

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of NAVISAS by small aircraft, the consortium presents the possible operational gains for an APNTsystembasedonNAVISASforsmallaircraft.

Thedocumentisstructuredasfollows:

Chapter2 Provides the stateof the art onnavigation techniques and current SESARworkonAPNTandpossibleapplicabilitytosmallaircraft.

Chapter3 Presentsthestateoftheartanalysesforboththeminiaturizedatomicclocksandtheminiaturizedatomicgyros.

Chapter4 Explains thesteps takentoassess thecurrentTRLof theNAVISASatomicgyroandpresents the experimental setup used by the consortium to implement the tests that enable theconclusionthatTRL2.5hasbeenachieved.

Chapter5 Provides a rationale for not advancing further on the development of the buildingblocksofNAVISASandproposesasetoroperationalgainsforaNAVISASbasedAPNTsystem.

Chapter6 Comprisestheconclusionsderivedfromthevariousactivitiescarriedout.



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StateoftheArtinnavigation

ConcerningthefirstsetofactivitiesofWP3,theconsortiumanalysedseveralnavigationtechniquesincludingthefollowing:

• GlobalNavigationSatelliteSystem(GNSS)• SpaceBasedAugmentationSystem(SBAS)• GroundBasedAugmentationSystem(GBAS)• CombinationofGNSSwithInertialNavigationSystems(INS)• CombinationofINSwithradar• CombinationofINSwithimagery• Beaconbasednavigation

o NonDirectionalBeacons(NDB)o VHFOmnidirectionalRadiorange(VOR)o DistanceMeasuringEquipment(DME)

• SignalsofOpportunity(SoOP)basedono ReceivedSignalStrength(RSS)o AngleofArrival(AOA)o TimeDifferenceofArrival(TDOA)o Pseudorangemeasurement

Notallof the techniquesmentionedaboveapply tosmallaircraft.Theyhavebeen included in theanalysisnonethelessforcompleteness.Foralltechniques,theconsortiumdescribestheprincipleofoperation,assessesthematurityofthetechnique(e.g.whilebeaconbasednavigationisstateofplay,SBAS is state of the art and SoOP is still in infant research phases), identifies the equipage andinfrastructureneedsanddescribestheperformancesachievable.

Relevantresearchactivitiesinthesedomainshavealsobeenidentifiedandreferenced.

Afterwards,anoverviewofwhattechniquesarecurrently inusebysmallaircraft ispresented.TheconsortiumalsoaddressescurrentSESARR&DactivitiesconcerningAPNTandassess theirpossibleapplicabilitytosmallaircraft(GA,VLA,ULandUAVs).

2.1 Beaconbasedtechniques

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2.1.1 Principleofoperation

Theuseofradiobeaconsfornavigationhasbeentheprimaryformofnavigatinginaviationforyears.Groundstations,thelocationofwhichisgivenincharts,broadcastspecificsignalsthathelplocatetheaircraftinrelationtothestation.Thisrelativepositioncanbeknownintermsofheading,distance,orboth.

2.1.1.1 NonDirectionalBeacons(NDB)NDB’sareaninexpensivewaytoimplementradiobeaconsfornavigation.Anomnidirectionalantennabroadcastsasignal,thefrequencyofwhichisknownandbetween200MHzand1.6GHz.Aboardtheaircraft,asystemwithadirectional,rotatingantennacantellinwhichthedirectionthesignalisthestrongest. Using that information, combinedwith the current heading of the aircraft, the pilot ornavigatorisabletoreducethepossiblepositionoftheaircrafttotwoopposedcones,centredonthebeacon,takingintoaccountinaccuraciesofthesystem.Usingtwoofthesemeasurements,thelocationoftheaircraftcanbededuced.

2.1.1.2 VHFOmnidirectionalRange(VOR)TheVOR isusedtoknowtherelativepositionof theaircraft.UnlikeNDB’s, theaircraftequipmentrequiresnomovingparts.Thestationbroadcastsoneomnidirectionalsignalatalltimes(a30Hzsignalmodulated),andonerotatingsignalthatrotatesat30revolutionspersecond.Thephasedifferencebetweenthetwosignalsisthentheanglebetweenmagneticnorthatthestationandtheaircraft.Anindicatorintheinstrumentpanelshowsthisangle,whichisknownasaradial.

2.1.1.3 DistanceMeasuringEquipment(DME)TheDMEisapulse-basedsystemthatallowsanaircrafttoknowitsdistancetoastation.Theaircraftinterrogates a stationwith a set of pulses. The ground beacon then retransmits the pulses to theaircraftinadifferentfrequency,afterasetdelayof50microseconds.Fromthetimedelay,thedistancetothestationcanbecalculated.Withthisinformation,theaircraftpositioncanbereducedtoatoroidregioncentredonthestation.DME’sarefrequentlycoupledwithVOR’stoproduceanestimateoftheexactaircraftposition.Eachbeaconisrequiredtohandleatleast50aircraftsimultaneously,however100isamoretypicalnumber.



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Figure1-VOR/DMEbeacon

2.1.1.4 InstrumentLandingSystem(ILS)The ILS isabeaconbasednavigationsystemthat ismeant toassistwithapproachesand landings,especiallyinconditionsofpoorvisibility.ForeachILSinstallation,threetypesofsignalsareprovided:

• Localizer–Attheendoftherunway,oppositeoftheapproachingdirection,twoAMsignals(at90and150Hz),slightlyoffsetfromtherunwaycentreline,arebroadcast.Aboardtheaircraft,theamplitudesofthetwosignalsarecompared.Iftheyarethesame,theaircraftishorizontallyalignedwiththerunwaycentreline.Thesesignalsprovidelateralguidance;

• GlideSlope–Besidetherunway,anotherpairofAMsignalsworkinthesamewayastheLocalizer,butwiththeequal-amplituderegiononanoptimalglidepath,thusprovidingverticalguidance;

• Markerbeacons–Placedatknowndistancesfromtherunway,thesealertpilotsoftheirprogressalongtheglidepath.

2.1.2 Maturity

These systems are fully developed and deployed. For commercial aircraft, the use of thesetechnologiesisbeingphasedoutinfavourofGNSSnavigation.Theyarestillused,forsomeapplication,suchasmarkingthelocationwhereanapproachorlandingusingILSistobeinitiated.

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They’restillusedforinstructionalpurposesingeneralaviation,buttheGNSSreceiversinthistypeofaircrafttypicallyofferdatabasesofthegroundbeacons,sotheycanbeusedforflightplanning,notnecessarilyusingthebeacons’signalstodeterminetheposition.

ForUAVs,thistypeofequipmentdoesn’tposeasignificantadvantage,soit’sdisregardedinfavourofGNSS+Inertialnavigation.

2.1.3 Equipageandinfrastructure

Thistypeofnavigationisdependentonthegroundstationsontheground.Furthermore,requiredon-boardequipmentincludesantennasandreceivers/transmitterstocommunicatewiththebeacons,andmeans to display the location or make it useful, such as display panels or interfacing with FlightManagementSystems.

2.1.4 Performance

MinimumaccuracyforNDB’s,asdictatedbyICAO,isof±5°.At100NM,thisresultsinanaccuracyof8.72NM.

ForVOR,thepredictableaccuracyisof±1.4°.At150NMawayfromthebeacon,thismeansthattheaccuracyisof±3.66NM.However,studiesshowthat99.94%ofthetime,theerrordoesnotexceed±0.35°.Atthesamedistanceof150NM,theaccuracyis±0.92NM.

TheaccuracyofDMEis±185m.It’simportanttostatethatthisdistanceisinstraightlinefromthestationtotheaircraft,andtakesintoaccountthealtitudedifference.

2.2 GlobalNavigationSatelliteSystems(GNSS)


NavigationthroughGNSSisbasedonsignalstransmittedbythesatellites.Thesetransmitparametersthatareusedtolocatethesatellitevehiclepreciselyonorbit,aswellasperiodicaltiminginformation.Bymeasuringthetraveltimeofthesignalspertainingtoseveralsatellites(whichcanbedistinguishedsincetheyhaveuniquesignatures),thereceiver’sposition,velocityandtime(PVT)canbedeterminedwith accuracy. This travel time is computed by differencing the arrival and departure time of thesignals,whicharecontaminatedwithclockerrorsfromboththereceiverandsatellite.Forthisreason,thisdistanceisknownasapseudorange.

Whilethispositioningcanbedoneautonomously,itcanalsobecomplementedwithdatafromnearbybase stations, the location of which is known with a very high degree of accuracy. This type ofpositioningisknownasDifferentialGNSS,orDGNSS,andreliesonthefactthatfornearbyreceivers,thesignalpathisroughlythesame,andsoaretheatmosphericdelaysthatoccuronthetroposphere



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andionosphere,whichcanbecancelledbydifferencingpseudoranges.Furthermore,thesatelliteandreceiverclockerrorscanbecancelledbysuccessivelydifferencingmeasurements,whichallowrelativepositioningtobedonewithahigherdegreeofaccuracythanthatofautonomouspositioning.

2.2.2 Maturity

AmultitudeofGNSSaredeployedandreadyforuse.TheUnitedStates’GlobalPositioningSystem(GPS) andRussianGLONASS are the systems that display the highest level ofmaturity, having fullconstellations operational. BothGPS andGLONASS exclusively use constellations inMediumEarthOrbits(MEO),withGPSusing6distinctorbitalplaneswithaninclinationof55degrees,andGLONASSusing3orbitalplaneswitha64.8degreeinclination.

The People’s Republic of China is currently deploying the Beidou System,with an expected globalcoverageby2020.Itisexpectedtocontaingeostationary,inclinedgeosynchronousandmedium-earthorbitsatellites.Atthispoint,coverageisnotglobal,andstartedinthevicinityofChina,expandingwitheachsatellitelaunch.Thefullconstellationisexpectedtohave35satellites.

TheEuropeanUnionhasalsolaunchedanefforttodeployaGNSS.CalledGalileo,anddevelopedbythe European Space Agency in conjunction with the European GNSS Agency. The system startedoperatinginDecember2016,initiallywith18satellitesinorbit.Thefullconstellationisexpectedtohave27activesatellitesand3spares,andtobeoperationalby2020.

There are also regional satellite navigation systems, developed to be used autonomously or inconjunctionwithdatafromotherglobalsystems.IndiahastheNavigationIndianConstellation(NAVIC,formerlyIndianRegionalNavigationalSatelliteSystemorIRNSS),withsevensatellitevehicleswhichorbitabove the Indiansubcontinent,while Japan’sQuasi–ZenithSatelliteSystemconsistsof threesatellitesinHighlyEllipticalOrbits(HEO)andonegeostationarysatellite.

Figure2-ComparisonbetweentheconstellationsofseveralGNSS

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GlobalNavigationSatelliteSystemsaretypicallydividedintothreesegments:

• The Space Segment consists of the satellite constellation, which, as mentioned before,regularlybroadcastsignalspertainingtothesatellitevehicle’spositionandtime.

• TheControlorGroundSegmentconsistsofthestationornetworkofstationsthatmonitorsthehealthandorbitsof thesatellites, issuingcorrections,predictingtheorbitsandmakingsurethebroadcastinformationisaccurateanduptodate.

• TheUser Segment ismade up of all the receivers that use the signals to determine theirposition, velocity and time. Since there is no communication from the receivers to thesatellites,thecapacityofthiskindofsystemsislimitless.

Autonomous GNSS is used in hobby grade UAVs for mission planning and path following, but itsperformanceintermsofintegrityisnotsuitableforcivilaviation,inparticularforcriticalflightphasessuch as approach and landing. Thus, augmentation systems have been developed to increaseperformance.Thesecanbesatelliteorgroundbased.

HobbygradeUAVsusuallyreceivelocationfromGPSreceiversusingtheNMEAstandard,offeredbymakerssuchasSiRFandu-blox.ForGeneralAviationuse,Garministhemostpopularmaker,andoffersa range of GPS units which feature databases of conventional waypoints, such as VOR and DMEbeacons,andnewerRNAVwaypoints.

Figure3-TypicalGeneralAviationgradereceiver(Garminaera796)



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Figure4-TypicalUAVreceiver(u-bloxLEA-M8T)

2.2.4 Performance

ThemainadvantageofGNSSpositioningistheabilitytoaccuratelydeterminethepositionandvelocityofavehicleinacontinuousway,regardlessofweatherconditionsandamountoftraffic.Commerciallyavailablereceiversareusuallyablecomputeposition informationwithanaccuracyof10metersorbetter.

Despite the GPS having a good track record for availability, autonomous GNSS are not totallydependableandarenottobeusedasthesolemeansfornavigation.AlargeconcernwithGNSSisthatofintegrity,ortheabilityofthesystemtotellwhetheritshouldbeusedfornavigation.TocomplywithRNP, the receiver is required to feature Receiver Autonomous IntegrityMonitoring (RAIM),whichprovidesintegritytothesystembydetectingfailuresinsatellitesignalsanddisregardingthemfromthe position computation. Some installations have been certified for B-RNAVor RNAV 5 (accuratewithin+/-5NM95%oftime)underIFR.

2.3 SpaceBasedAugmentationSystem(SBAS)


SatelliteBasedAugmentationSystems(SBAS)areatypeofsystemthatcomplementsGNSSsolutionsby improving accuracy, reliability or availability. Ground monitoring stations perform rangingmeasurementstoGNSSsatellitesanduploadcorrectiondatatosatellites.ThesatellitesthenbroadcastcorrectionparameterspertainingtotheGNSSvehicles(suchasfinerclockcorrectionsormoreaccurateephemerides)orthepropagationmedium(liketheionosphereandtroposphere).Thesecorrections

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can’t account for the receiver-related errors (such as multipath and the local characteristic oftroposphericeffects).Coverageofthesesystemsisusuallyreservedtoacontinentorregion.Apartfromthat,SBASvehiclescanbeusedasagenericGNSSvehicle,itspseudorangeaidingthepositioncomputation.ErrorsdetectedbySBASaretransmittedandcanbeusedbytheenduserwithinaslittleassixsecondsofamalfunction.

2.3.2 Maturity

There are a number of SBAS, their maturity ranging from deployed and ready to be used, todecommissionedinfavourofnewer,bettersystemsthatcoverthesamearea:

• TheWide Area Augmentation System (WAAS) is developed by the United States’ FederalAviationAgency(FAA).Itconsistsofanetworkof38groundstationsinthecontinentalUnitedStates,Alaska,Hawaii, CanadaandMexico, three geostationary satellites, and its intendedareaofcoverageisNorthAmerica.ItonlysupportsGPS.

• The European Geostationary Navigation Overlay Service (EGNOS) is developed by theEuropeanSpaceAgency,theEuropeanCommission,andEUROCONTROL.Thegroundnetworkconsistsof34ReceiverIntegrityMonitoringStations(RIMS),whichreceivetheGNSSsignals,4MasterControlCenters (MCC–oneactive,onehotbackup, and twocoldbackups),whichprocess the data, and 6 Navigation Land Earth Stations (NLES – two for each satellite forredundancyreasons),whichuploadthedatatothesatellites. Theconstellationconsistsofthree geostationary satellites, and its intended area of coverage is Europe. It providescorrectionsforGPS,GLONASSandGalileo.

• Japan’sMTSATSatelliteAugmentationSystem(MSAS)isownedandoperatedbytheJapaneseMeteorological Agency and Japanese Ministry of Land, Infrastructure, and Transport. ItsupplementstheGPSinasimilarwaytotheformertwosystems.Fourgroundstationsreceivethesatellitesignals,whichareforwardedtotwoMasterControlStations(oneforeachsatelliteinorbit),whichprocessthemandcalculatethecorrectionsandsendthemtothesatellites.

• India’sGPSAidedGeoAugmentedNavigationSystem(GAGAN)providesSBASserviceontheIndiansubcontinent.Itfeaturesthreegeostationarysatellites,maintainedbytwobasestationsthatprocessthedatafrom15referencestations.

• TheRussian Federation is currently developing the System forDifferential Corrections andMonitoring(SDCM),tocomplementtheGPSandGLONASSsystemsinRussia.Threesatelliteshavebeenlaunched,whichbroadcastcorrectionsbasedondatacollectedby19stations inRussiaand5stationsabroad.OnecentralprocessingfacilityinMoscowprocessesanduploadsthedata,alongwithonereservefacility.

• TheSatelliteNavigationAugmentationSystem(SNAS)isbeingdevelopedbyChina,althoughverylittlepublicinformationisknownatthemoment.

• TheStarFiresystemhasbeendevelopedbytheJohnDeereCorporation,tobeusedwiththeirGPSreceivers,forfarmingandfieldsurveyingapplications.



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• Canada had theGPS Correction (GPS-C) service,whichwas deactivated since it required aseparatereceiver,makingitlesscosteffectivethanWAASorStarFire.

Figure5-GlobalcoverageofseveralSBAS


SatelliteAugmentationofGNSS is relianton theconstellationandgroundcontrolnetworkofeachsystem,which is particular to each implementation. Furthermore, the GNSS receiver onboard theaircrafthastobecompatiblewithSBASmessages.Asexplainedbefore,theSBASsatellitescanbeusedasagenericGNSSvehicle,computingthepseudorangefromthesignal travel time,but itsgreatestadvantageare thecorrectionmessages thatallowthereceiver tocancelapartof thesatelliteandpropagationmedium-relatederrors.

2.3.4 Performance

Augmentationsystemsare,as statedbefore,notused independently,but instead improvealreadyavailableGNSS.Themainconcern,forairborneapplications,isthatofintegrity,ortheabilitytotellwhether the system should be used for navigation purposes. A secondary objective is to increaseprecision.AchievableSBASperformancerequirementsinclude:

• En-routeRNP4(Oceanic/Continental),forahorizontalaccuracyof4NM(95%);• En-routeRNP2(Continental),forahorizontalaccuracyof2NM(95%);

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• En-routeRNP1(Terminal),forahorizontalaccuracyof1NM(95%);• Non-PrecisionApproach,forahorizontalaccuracyof220m(95%);• APV-I,forahorizontalaccuracyof16m,andverticalaccuracyof20m(95%);• APV-II,forahorizontalaccuracyof16m,andverticalaccuracyof8m(95%);• Category I precision approach, for a horizontal accuracy of 16 m, and a vertical accuracy

between6and4m.

2.4 GroundBasedAugmentationSystem(GBAS)


ManyoftheprinciplesthatSBASisbasedonapplytoGBAS.However,GBASisintendedtohaveamuchsmallerareaofcoverage,generallyinthevicinityofanairport.Thistypeofsystemwasdesignedtoaidintheapproachandlandingphasesofflight,providinganalternativetotheInstrumentLandingSystem(ILS).TheimplementationofGBAStoprovideapproachandlandingcapabilityiscalledGLS.SeveralGNSS receivers in the area forward the satellite signals to a base station, which computes thecorrectionsandbroadcaststhem.Themessagesstandardincludes,inadditiontotheGNSSdifferentialcorrectionsandintegrityinformation,GBASrelateddata,andinformationabouttheFinalApproachSegment,withsupportformoremessages.

ThemainadvantageofGBAS/GLSoverILSisinthefactthatforoneairfield,onlyoneGBASequipmentisrequired,regardlessofthenumberofrunways.ForILS,onelocalizer/glideslopepairisneededforeachrunwayandheading. Italsofreesuptheelectromagneticspectrum,sinceoneGBASstationiscapableofbroadcastinginformationforupto48approachprocedures.



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Figure6-ArchitectureofGBAS

2.4.2 Maturity

SeveralairportsworldwidehaveapprovedsystemsinplaceforCategoryIprecisionapproaches.AsofFebruary2015,twolocationsintheUnitedStates(NewarkandHouston)andtwentyintherestoftheworld(includingfourinEuropeandfifteeninRussia)supportedtheGBASLandingSystem(GLS),withplanstoimplementthesysteminmorelocations.

SeveralavionicsmanufacturersprovideaircraftequipmentthatisapprovedbytheregulatingbodiestobeusedforGBASapproaches,andarebeing installed innewcommercialaircraftbyBoeingandAirbus.Forsmallaircraft,itisatechnologywithinterestintheGeneralAviationcategory,sinceitoffersanalternativetotheILS.


SinceitaugmentsoneorseveralGNSS,thebasicequipmentforthesesystemsisrequiredonandoff-boardtheaircraft.Theseincludethesatellitesandgroundstationswhichmonitorthemandcontrolthem,andthebasicGNSSequipageaboard(receiver(s)andantennae).

Furthermore,eachairfieldrequiresseveralGNSSreceiversandantennae,aunitthatretrievesthedatafrom the receivers and processes it, and a radio transmitter to broadcast the GBAS signal. ThesetransmissionshappenoverVHFDataBroadcast(VDB).

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2.4.4 Performance

GBASiscurrentlyratedforCategoryIapproaches.Therequirementsinclude

• Horizontalaccuracyof16m(95%);• Verticalaccuracybetween6and4m(95%);• ATime-to-alertof6seconds,incaseofmalfunction;• Availabilityof99%orbetter.

2.5 InertialNavigationSystems(INS)


Inertial Navigation Systems allow the determination of vehicle position and attitude, by directlymeasuringtheaccelerationsandangularvelocitiestheaircraftissubjectedto.

Thishasthreemainadvantages:

• Thesensorshaveveryquickresponse,soveryhighdataratesandbandwidthscanbeachieved;• No external equipment is required, so the system is self contained and not vulnerable to

jamming.It’salsonotdependantongroundstationsorsatellitevehicles;• Itprovidesveryaccuratemeasurementsofposition,groundspeed,azimuth,andvertical.

Thereare,however,severaldisadvantages:

• Thepositionaccuracydegradesovertime;• Highendapplicationsareexpensive,especiallyifwefactorthatmultiplesensorsofthesame

typeareoftennecessaryforredundancyreasons;• Thesystemneedstobeinitiallyaligned.Itiscommonlydonewhentheaircraftisparked,since

airfieldchartsoffercoordinatesforitsapronspacesorgates;• Theaccuracyofthesolutionisdependentonthemanoeuvresperformedbythevehicle.

Inertialnavigationsystemsarealmostalwaystheconjunctionoftwotypesofsensors:

• Accelerometers–measureaccelerationalongaparticularaxis.Accelerationisthenintegratedovertimeoncetodeductvelocity,andintegratedonemoretimetocomputedisplacementfrom original position. The basic concept is that of sensing the force applied on a looselysuspendedmass.Sincetheequipmentisrigidlyattachedtotheaircraftbody,thiscorrelatestotheaccelerationtheaircraftisexperiencing.

• Gyroscopes–provideameasurementoftheattitudeoftheaircraft.Earlyimplementationswerespinningmassesorwheels,whichtendtoholdtheirposition,andassuchprovidethe



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angular displacement from a nominal position. More sophisticated models usemicroelectromechanicalsystems(MEMS),ortakeadvantageoftheSagnaceffect(fiberopticgyroscope–FOG,andringlasergyroscope–RLG),ortheCorioliseffect(VibratingStructureGyroscope–VSG)

Since these devices measure accelerations and angular velocities in one axis, three of each,perpendiculartoeachother,areneededtocompletelydefinetheaircraftorientationandposition.

2.5.2 Maturity

Thedevicesthatallowinertialnavigationtobeperformedareavailableonthemarket,itscostvaryingfrom a few Euros for a six axis Gyroscope + Accelerometer device (such as the MPU-6050 fromInvensense,frequentlyusedinhobbygradeUAVs)tohundredsofthousandsofEurosfornavigationgradeinertialnavigationsystems(suchastheHoneywellHG9900,usedincommercialaircraftwhichusually employmultiple units to average themeasurements and for redundancy purposes). Evenhigherendsolutions,suchasthoseformarineapplications,cancostintheneighbourhoodof1millionEuros.Apartfromthemoreaccuratemeasurement,higherenddevicessupporthighersamplerates,anddisplaylessdegradationovertime.


Inertialnavigationrequiresnoexternalequipment.Commercialproductscombineaccelerometersandgyroscopes for all three axes, and these communicate directly with the flight computer, be it amicrocontroller forhobbygradeUAVs, or a FlightManagement System. These systemsare also inchargeoftheinitialcalibrationoftheInertialNavigationSystem.

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Figure7-Twoexamplesofinertialplatforms.Left:abreakoutboardoftheInvensenseMPU-6050.Right:TheHoneywellHGU1930

2.5.4 Performance

Sinceweareonlyabletodirectlymeasureaccelerationsandangularvelocities,anyaccelerationerrorwill get amplified quadratically over time. For this reason, inertial measurements are never usedexclusively, since implementationscandivergeupseveral thousandkilometreswithinonehour forcheaperplatforms.Navigationgradeplatformswilltypicallydivergeafewkilometreswithinonehour,andthiscanbemitigatedbyusingseveralindependentsensorsandusingalgorithmssuchasKalmanFiltering.TheindependencethatINSdisplaysofotherexternalnavigationsaidsmadeitoptimalforuseinoceanicoperations,sincethenavigationalrequirementsintermsofaccuracywereof20nauticalmilesacrosstrack,and25nauticalmilesalongtrack.

2.6 GNSSplusINS


CombiningGNSSandInertialNavigationbringsanumberofadvantages.FirstofalltheGNSSpositionsolutiondoesnotdrift, so it canbeused to tellwhether the inertialplatform isdrifting toomuch.Conversely, inertial platforms reach much higher sampling rates than GNSS, so they can providepositionbetweenGNSSupdates,orthesignalislost.Themeasurementsfromtheseveralsystemsareused by a Kalman Filter or Extended Kalman Filter to provide position and attitude updates. Thefollowingtablesummarizesthemaincharacteristicsofeachtechnique.

Satellitenavigation Inertialnavigation–Absolutepositiondata –Driftinintegratedterms–Limitedresolution –Highresolution(rel.)–Slow –Fast(kHz)



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–Worseatorientation –Bestatorientation–Easilydisturbed –Disturbance-free(noexternalref.)–BestatX&Y –BestatZ

Table3:comparisonbetweensatellitenavigationandinertialnavigation

2.6.2 Maturity

GNSS+INSnavigationiscurrentlyavailableforcommercialapplicationsineverycategoryofaircraft.Forcommercialaircraft,itisthemainwayofnavigatingoceanicairspaceandcontinentalremoteareas.For small aircraft, UAVs use the combination of sensors for control and path following purposes;GeneralAviationusersutilizetheinertialplatformforcontroloftheaircraft,whileGNSSaugmentstheconventionalnavigationexperienceby implementingdatabasesofconventionalbeacons (e.g.VOR,NDB)andnewerRNAVwaypoints,withouttheneedtoresorttoflightcharts.


The inertial part of the system is, as stated before, self-contained and independent of externalnavigationaids.Itrequiresone(orseveral,forredundancy)InertialNavigationSystemsthatdeductthepositionandattitudedirectlyfromtheaccelerationsandangularvelocitiesoftheaircraft.

TheGNSSpart requires specialized receiversaboard theaircraft, and isdependenton the satellitevehiclesandnetworkofgroundstationsthatmonitorthem.

Using the two systems in tandem requires a third piece of equipment aboard the aircraft, whichreceives the data from theGNSS receivers and the inertial platforms and uses algorithms such asKalmanFilteringtooutputtheposition,velocityandattitudeof theaircraft.This isknownas flightmanagementsystem(FMS)andcanalsointerfacewithradionavigationsystems.

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Figure8-TheTrimbleAP20,aGNSS+Inertialplatformwhichcanbeusedforairborneapplications

2.6.4 Performance

Navigation using GNSS combined with inertial platforms is used in en-route operations, beingemployedforthefollowingtypesofPerformance-BasedNavigation(PBN):

• En-routeRNP10(Oceanic/RemoteContinental),forahorizontalaccuracyof10NM(95%);• En-routeRNP4(Oceanic/RemoteContinental),forahorizontalaccuracyof4NM(95%);• En-routeRNP2(Continental),forahorizontalaccuracyof2NM(95%);• En-routeRNP1(Terminal),forahorizontalaccuracyof1NM(95%);• Non-PrecisionApproach,forahorizontalaccuracyof220m(95%);

2.7 INSplusRadar


One other way that INS measurements might be augmented is by combining them with RadarObservations.Specifically,byusingseveralmicrowavesignalspointingindifferentdirections(atleastthreenoncoplanarbeamsarerequiredtodeterminevelocity,typicallyfourbeamsareused),andbymeasuring Doppler shifts, one can infer the aircraft velocity, which can be integrated to finddisplacementfromaknowninitial location.Thisplaystothetwosystems’strongpoints,asittakesadvantageofthesmalllong-termvelocityerroroftheDopplerradar,andthesmallshort-termvelocityerroroftheinertialplatforms,whichareknowntodivergeoverlongperiodsoftime.

Thisconjunctionhasthefollowingadvantages:



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• Velocity ismeasuredrelativetotheEarth’ssurface.Airdatasystemsmeasurevelocitywithrespecttotheairmass(whichisrelevantforaerodynamicpurposes),andmostterrestrialradionavigationsystemsmeasurevelocitybydifferencingsuccessivepositionmeasurements;

• Itisaself-containedsystem,meaningitrequiresnoexternalequipmentorinfrastructure.Thisalsomeansthatitrequiresnointernationalagreements;

• Airbornetransmittershavelowpowerrequirements,whichmakesthemlowweight,size,andcost.

• Theradarbeamsarenarrowandpointedatsteepanglestowardstheground,whichmakestheaircrafthardtodetect;

• Itworksineverytypeofweatherconditions,saveforextremeconditionsofrain;• Itcanoperateoverlandandwater(exceptforcompletelystillwaterbodies);• Itprovidesveryaccurateaveragevelocityinformation;• UsingDopplerradarisverysuitableformeasuringthree-dimensionalvelocityatlowspeeds,

whichisrequiredwhenhelicopterandmulti-rotoraircraftarehovering.

Itdoes,however,havesomedisadvantages:

• Vertical reference information (such as that of an altimeter) is needed to convert velocityinformationintopositionalcoordinates;

• Likestandaloneinertialnavigation,itsaccuracydegradesovertime;• Instantaneous or short-term velocity output is not as accurate as averaged or smoothed

velocity;• Whileoperatingoverwater,accuracy isdegradedduetobackscatteringcharacteristicsand

watermotion.

2.7.2 Maturity

Aswithmost technologies, airborne Doppler radar velocitymeasurement had its inception in themilitary.Itwasfirstusedforairbornemovingtargetindication,aswellasvelocitydeterminationbycombining itwithairspeed indicators. Inthe1960’s,thismigratedtocommercialaviation,where itbeganbeingusedprimarilyforoperationsinoceanicareas,byjoiningitwithinertialplatforms.

By the 90’s, thebiggest useofDoppler radarwas inmilitary helicopters, for navigation aswell asoperationssuchashovering.TheywerealsodeployedinUAVsanddrones.

Despitebeingafullydevelopedtechnology,theuseofDopplerradardidn’tbecomewidespreadsinceit suffers fromoneshortcoming thatalsoaffects inertialnavigation, i.e., its solutiondegradesovertime.Duetothis,thesesystemsareoftencoupledwithGNSS.GNSSsolvestheinitialisationproblems,while Doppler radar provides continuity when GNSS signal is lost, be it due to terrain, aggressivemanoeuvres,orjamming.

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Sincethisisaself-containedsystem,noexternalequipmentisrequired.Theonlyon-boardequipmentneededistheinertialplatform,theradartransmitter/receiverequipment,andtheflightcomputerthatcouplesthetwomeasurements.

2.7.4 Performance

StandaloneDopplerradarhasatypicalvelocityaccuracyof0.06m/s±0.2%,whilehighperformanceimplementationsareusually a factorof twobetter. Forpositioningperformance, couplingwithaninertialplatformcanyieldanaccuracyofabout0.15%ofdistancetravelled.ItisimportanttomentionthatDopplerradarshaveaserviceceiling,whichistypicallyofatleast3000maboveterrain.

Asstatedbefore,performanceispooreroverwater,sincethescatteringcoefficientvarieswiththeangleofincidence,whichcausesvelocitytobeunderestimated.Theseerrorscanbeaslargeas5%andevenlargeroververystillbodiesofwater.Oldersystemsprovidedtheuserwithtwoswitchablemodes,oneforuseoverland,andoneoverwater,whichcouldreduceresidualerrorstoaslittleas0.3%,whilenewersystemstypicallyuseadifferentbeamshape.

2.8 INSplusimagery


Becauseofthequickdriftofstandaloneinertialsolutions,severaltechniqueshavebeendevelopedtogetaroundtheselimitations.Forindoorapplications,visiondatafromoneormorecamerascanbeused to complement the inertial system’smeasurements. These techniques use image processingalgorithms,whichtake intoaccountthewidthof fieldofview,aswellas theframerateandotherparameters,toaccuratelyestimatethechangeinorientationandpositionovertime,independentlyfromtheinertialplatform.ThiscanthenbefedintoaKalmanFilterwhichcombinesthemeasurementstoreturnasolutionforposition,velocityandorientation.

2.8.2 Maturity

Thistypeofnavigationhaslittleapplicabilityforoutdooraircraft,sinceseveralGNSSareavailableandtheirprecision isappropriate foralmostallphasesof flight,butadvancementsarebeingmade forindoorUAVs.Thisis,however,stillahighlyexperimentalfield.

In his 2014 PhD thesis (http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000017227/Stereo-Vision-Aided_Inertial_Navigation.pdf), Grieβbach develops a navigation system based on inertial



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measurementsandstereovision(dualcamerastosimulatethehumaneyesight).Theconclusionwasthatthemeasurementscomplementedeachotherquitewell,itsaccuracybeingasgoodas2%,oradeviationof74centimetresina310metrerun.


Thereisnoneedforoff-boardequipmentforthistypeofnavigation,allprocessingisdonebasedonphysicalvariablesdirectlyobservablebythesensors.

However,itrequiresoneormoreInertialMeasuringUnits(IMUs),oneormorecameras,andaCPUthatiscapableofrunningtheimageprocessingalgorithms.

2.8.4 Performance

Giventherelativelylowlevelofmaturityofthesetechniquesitisriskytoadvancespecificvaluesfortheirperformance.Nevertheless,R&Dworksuchastheonementionedabovehasshowndeviationsof74centimetresovera310metrerun.

2.9 SignalsofOpportunity(SoOP)


Thedesignation“SignalsofOpportunity”(SoOP)referstotheuseofsignalsthatarenotintendedfornavigationalpurposes.SignalsofOpportunityhaveseveraladvantagestotheuser:

• Quantity–Therearemanysignalsavailable.TheseincludeanalogueanddigitalTVbroadcaststations,AMandFMradio,andBluetooth,Wi-Fi,andcellularnetworks;

• Highpower–GNSStransmitterssuchasGPShavepowerconsumptionrestrictions,sotheirtransmittedpowerisquitelow.HighpowerSoOPtransmittersignalscanpenetratewalls,sotheycanbeusedforindoornavigation;

• Noinfrastructurerequired–Thetransmitterinfrastructureisalreadyinplace,sincethesignalsarealreadybeingtransmittedforotherpurposes;

• Technology is making it more feasible – The main advancement in this regard is that ofSoftware-DefinedRadio (SDR),where receivers canquickly switch frequencies and analyzedifferent typesof signals, resorting toacomputer thatcontrols the receiverandprocessesthesesignals.Usingseveralfrequenciesalloverthespectrumalsoreducesthepotentialforjamming.

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Theyare,however,notwithoutdrawbacks:

• Notoptimizedfornavigation–Themaindisadvantageof this is timing. Inordertousethetraveltimeofthesignaltodeterminethedistancetothetransmitter,theexacttransmissiontimemustbeknown.Mostcommunicationsystemsdonotprovidesynchronizationtowithinafewnanoseconds(likeGPSdoes),andusuallyrequireanadditionalreferencereceiver.

• Varyingavailability–Thetransmittersaremuchmorecommoninornearbyurbancenters,and rarer in remote or rural areas. Moreover, different countries might have differentfrequencyandprotocolstandards,whichcanmakeimplementationmorecomplex.

• Transmitter locationsmustbe known– Likebeaconbasednavigation, the locationsof thetransmittersarenecessaryinformationtolocatethereceiver.Moreover,thereareoccasionswhere several transmitters are located closely together,which introduces a factor of poorgeometry,andmakesitsothatinpractice,onlyoneofthosetransmittersshouldbeused.

• Challengesbuildingthenavigationequipment–despitetheadvancementinSDRtechnology,therearealotofconsiderationstohaveinmind.Awidebandantennaisneededsothatnopartofthespectrumistoodisregarded;highbandwidthandhighsampleratesareneeded,whichinturnrequiresprocessingpower.Thesesignalscanrangeinfrequencyfrom100KHz(AMradio)to5GHz(newerWi-Fisignals).

ThereareseveralwaysthatSoOPcanbeusedtodetermineareceiver’spositionandvelocity:

• ReceivedSignalStrength(RSS);• AngleofArrival(AoA);• TimeDifferenceofArrival(TDoA);• Pseudorangemeasurements

2.9.1.1.1 ReceivedSignalStrength(RSS)Sincethereceivedsignalstrengthdecreaseswiththedistancetothetransmitter,thedistancetothetransmittercanbeinferredfromthereceivedpower.Thisisdependentonknowingthetransmittingandreceivingpowers,aswellashavingamodelforthepathloss.Thebiggestdrawbackofthismodelisthatit’snotadequateiftherearemanyobstaclesbetweenthetransmittingstationandthereceiver,whichisthecaseforindoorapplications.

2.9.1.1.2 AngleofArrival(AoA)ThisworksinasimilarwaytoNon-DirectionalBeacons.Sincemostlong-range,broadcastingantennastransmitinanomnidirectionalpattern,arotating,directionalantennacanbeusedtofindtheheadingof the station. Combining twoof these allows the location of the receiver to be found, andmoremeasurementsincreasetheaccuracyofthesolution.



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2.9.1.1.3 TimeDifferenceofArrival(TDoA)This relies on a reference station relies onmeasuring the difference in arrival time between twodifferentreceivers.Ofcourse,it’sreliantontheclocksofbothstationsnotdivergingtoomuchfromeachother,butwithsignalsfromseveralsources,it’spossibletodeterminethepositionofamovingreceiver.

2.9.1.1.4 PseudorangemeasurementsSimilarlytotheGNSSoperation,ifthetransmissionandreceptiontimesareknown,thedistancecanbededucedbydividingthetransittimebythepropagationvelocity.It’sdependentonthetransmittingstationhavingsomekindofsignalthatrepeatsreliablyataknowntimeandrate.Ifthisisthecase,thereceivercanuseGNSSsignalfromonlyonesatellitetoensureitsownclockdoesn’tdivergetoomuch,andmeasurethetransmissiontimestofindthedistance.

2.9.2 Maturity

Fromthetechniquesexplainedabove,themostattractivetouseasanactualnavigationaidisperhapsthatofTDoAusingAMradio.AMsignalshaverelativelylowfrequencies,thereforelongranges,soaquantityofsignalsareavailable,fromcommercialradiostationsthatstillbroadcast,toamateurradioenthusiasts. In his PhD Thesis(https://pdfs.semanticscholar.org/73c9/e528570e38637454875140a6d54f4668c8bc.pdf), Halldevelopsaradiolocationsystemusingthecarrierphaseofthesesignals.Makingsuretheantennaepositions are accurate, one can expect similar accuracy to that of GPS in open areas. The mainadvantage,however,isthatthesesignalsaremorepowerfulandhavelowerfrequencies,sotheyareabletobettertopassthroughbuildingsandcanposeanadvantageinheavilyforestedareas,whereskyviewisobstructedandGNSSstruggles.OnedisadvantageofthissolutionisthatAMstationsarerequiredbylawtodecreasetheiroutputpoweratnight(sincetherecanbeskywavepropagationwhichinterfereswithotherstations),sotherearenotasmanysignalsavailabletobeusedduringnighttime.

Another implementation, from a 2005 paper titled “A New Positioning System Using TelevisionSynchronizationSignals”,writtenbyMatthewRabinowitz,usesdigitaltelevisionbroadcastsignalsforstandalonepositionortoaugmentGNSSpositioning.ThesesignalshavetheadvantageofsendingaSynchronizationSegmentwhichrepeatsataknownrate,andassuchtheydonotsufferofoneofthegreatestdisadvantagesofgeneral-purposesignals.TheyalsousemuchhigherfrequenciesthanAMradio,so they’renot limited inpoweratnight.And,sincethe frequenciesaren’tashighas thatofGNSS, the signals are able to penetrate buildings, allowing navigation in challenging urbanenvironmentsandevenindoors.


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Theoff-boardequipmentisalreadydeployedandactive.Intermsofonboardequipment,theantennaandreceiverneedtobeasversatileastherangeofsignalsinuse.Foramorevariedspectrum,widerbandwidthandhigherqualityequipmentisnecessary.Thisalsoinfluencesthecomputationalpowernecessary,althoughthisisnolongeratapremium,withsingleboardcomputersbeingaffordableandcapableofrunningSDRprograms.

2.9.4 Performance

Hall’simplementation,evenifjustaproofofconcept,usesthecarrierphaseofAMsignals,andisableofattainingprecisionsbetterthan15meters,95%ofthetime,fordistancesunder35kilometresfromthereferencestation.Fordistancesunder10kilometres,theerrorwassmallerthan7meters,95%ofthetime.ThisworkwasdevelopedlittleafterGPSprecisionstoppedbeingdegradedpurposefullyforsecurityreasons,andreceiverswerestillrelativelyexpensive.So,therewasavoidforlowcost,semi-precise positioning. At this time, with the plethora of GNSS available, there is little danger of aworldwideshutdownofeveryGNSS,andreceiversareinexpensive,sothisvoidisalmostnon-existent.

For the Rabinowitz system, accuracy of the system was similar to standalone GNSS in outdoorscenarios, andbetween4.4 and19.6metresof standarddeviation in indoorenvironments,whereGNSSisunabletolocateareceiver.ThissystemcancomplementGNSSsinceitperformswellinurbanenvironments,wheretransmittersaremorecommon,whileGNSSgenerallyperformsbetterinruralareas,whereDigitalTelevisiontransmittersarerarer.

However,oneaspectwheresignalsofopportunitycanbeveryusefulistoconstrainthedriftofinertialsystemsusingtheDopplerdeviationfromthenominalfrequency.

2.10 NavigationinGA,VLAandUltra-LightsManyGAaircraftarefittedwithavarietyofnavigationaids,suchasAutomaticdirectionfinder(ADF),inertialnavigation,compasses, radarnavigation,VHFomnidirectional range (VOR)andGNSS.Allofthesenavigationaidsmadehugeimprovements inaircraftnavigation.Today´stendency istomakenavigationeasier,morereliableandcosteffective.GNSScombinedwithcontinuouslyimprovedMEMSsensorsandnewadvancedtechniquesmighthavebigimpacttonavigationsystemsofsmallaircraft.ThemaintechnologicalevolutionsunderwaywithapplicationtoGAincludemostofthetechniquesmentionedinprevioussub-sections:

• Augmentationofaglobalnavigationsatellitesystem(GNSS)• ApplicationofdualfrequencyGNSSreceivers(GPS-L1/L5)• UpcomingGalileoservices• ApplicationofMEMS(i.e.MicroElectroMechanicalSystems)inertialsensors• CombinationofInertiaandGNSStechniques(longtermprecisionforGNSS,dynamicand

autonomyforinertia).Althoughthemostrecentlydesignedcockpitsforgeneralaviationencompassanumberofnoveltiesintermofsafetyorcapability(satelliteweatherstatus,syntheticvisionsystem,trafficalert,infraredcamera,touchscreen,wirelesstransferofflightplansbetweenamobiledeviceandtheavionics…)thenavigationsensorshavenotbeenfollowingthistrend.



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Figure9:LatestGarminG1000NXicockpit

RelianceonGPS isnowastandard inGeneralAviationforVFRand IFRforseveralyears.All recentairborneGPSreceivers includeSBAScapabilityandarecompliant toTSOC145corTSOC146c.GPSpositionislargelyusedbytheavionicsandisfeedingallon-boardsystems(2Dmap,Syntheticvisionsystem,Trafficadvisory,ADS-B,..).BasicRNPcapabilitymayalsobeavailableonsomeaircraft.

ThenewIFR-designedavionicsareLPVcapable(meaningthattwoGPS/SBASreceiversareembeddedforsafetyissue).AnumberofolderaircraftsarealsoretrofittedwithLPVtoincreasetheiroperationalcapability or keep it unchanged following the decommissioning of ILS beacons replaced with LPVapproaches.

AlthoughintheUSorEuropegeneralaviationisallowedtoflyIFRequippedonlywithSBASreceiver(Title14→ChapterI→SubchapterF→Part91→SubpartC→§91.205)thiswillpreventthepilotfromflyingVORorNDBpublishedapproacheswhereoverlayisnotallowed.WithonlyGPS/SBASonboardthepilotwouldbelimitedtoRNAVandRNPIFRroutes.MoreoverincaseofGPSloss,VORorNDBremainasafebackupnavigationmean.That’swhyGeneralAviationavionicsusuallycomewithlegacyVORandNDBreceiversinadditiontotheGPS.GeneralAviationisusuallyneitherequippedwithDMEnorwithinertialunit(whichareacostlyandpowerconsumingdevice,andarenotrequiredbyregulation).

NewGNSS constellationsarenotusedyetonboardaircraft. TheGLONASSmandate in force fromJanuary1stonlytargetsaircraftweightingmorethan12,500poundsandregisteredonanoperationalcertificate issuedbyRussia’scivilaviationauthority.Galileo initialcapability isstill toorecenttobeoperationallyusedonboardaircraft.

2.10.1 Majorplayerslist

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The following is non-extensive list of the main manufacturers of navigation equipment for smallaircraft:

• AELSistemas(BR)(displaysamongotheravionicssystemsforfixed,rotarywingandunmannedvehicles)

• Aircraft Radio Corporation (US) (avionics and flight control system for GA aircraft such asCessna)

• AstronicsMax-Viz(US)(suppliersofEVSanddisplays)• AvidyneCorporation(US)(integratedavionics,displaysandtrafficadvisorysystems)• CheltonFlightSystems(US)(syntheticvisionsystemsandavionics)• DynonAvionics(US)(non-certifiedelectronicsincludingtransponders,autopilotsanddisplays)• Furuno(JP)(GNSSreceiversusedinbothmannedandunmannedaircraft)• Garmin(US)(GNSSreceiversusedinbothmannedandunmannedaircraft)• Honeywell(US)(suppliersofsensorsandinertials)• JPInstruments(US)(flightinstrumentsandenginemanagementsystems)• L-tronics(US)(DF,ELTandEPIRBequipment)• RockwellCollins(US)(communicationsystemsandavionicsforalltypesofaircraft)• S-TECCorporation(US)(autopilotsforsmallandmid-sizeaircraft)• ThalesAvionics(FR)(avionicsfordifferentcategoriesofaircraft)• TlElektronic(CZ)(manufacturerofinstrumentsandon-boardsystems)• UniversalAvionics(US)(FMSandinstrumentdisplaysforprivateaircraft)

ThevastmajorityofnewlydesignedglasscockpitforcertifiedaircraftuseaGarminintegratedavionicssuitefromtheG500(Piper),G1000(Cessna,Piper,Diamond,Cirrus,etc…),G1000NXi(KingAir),G2000(Cessna)orG3000(Socata)series.Thenavigationmeans(GPS,VOR)aredirectlyintegratedintotheavionics suite. Other avionicsmanufacturers target regional or business aircraft (Rockwell Collins,Honeywell),oronlyprovideGPSorVORreceivers thatcanbe included inanexistingavionics.ThefollowingfigureprovidesanexampleofaGarminsystemarchitecture.



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Figure10:GarminG1000architecturediagram

2.11 NavigationinUAVsandDronesCurrently,navigationinUAVsordronesisfundamentallybasedonGNSS(namelyGPS).GPSisoftencomplementedwithothertechniquesdependingonthesizeofthedrone.Atthispointitisimportanttodifferentiatebetweensmalldrones(oraccordingtoEASA’sproposedregulation,CATA0–toysandmini-dronesbelow1KgandCATA1–smalldronesbelow4Kg)andlargerdronesabove20Kg.WhiletheformermaynotevenhaveGPS(thecaseoftoys)andcanrelyonvideofornavigation,thelarger

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dronesoften combineGPSwith some formof commercial grade inertial sensors (accelerometers),video (as mentioned previously) or radar. For example several manufacturers achieve autolandcapabilitiesbycombiningGPSwithradio-altimeters.

Giventhatdroneshavenocockpitperse,instrumentsareprocuredbydronemanufacturersdirectlyto sensor, transducer orGNSS receiver suppliers. Themajority of sensor data is then representeddigitallyinGCS(GroundControlStations).ThemajorityofdronemanufacturerstendtodeveloptheirownGCSsothatdisplaysarethenprovideddirectlybytheplatformmanufacturer.Fromthelistofplayersabove,Garminisprobablythemostactiveinsupplyingthedronemarket.

2.12 CompatibilitywithSESARconceptsASESARA-PNTstudyhasbeenstarted inthecourseoftheSESARprojectaddressingtheemergingneed of aircraft resilience to GPS outage. The work is currently continued in the frame of theSESAR2020project.AparallelactivityisconductedbyFAAintheframeofNextGenproject.In2016,the FAA released its PBN NAS (Performance Based Navigation Strategy 2016) describing itsPerformance Based Navigation roadmap including resiliency to GPS outage. The major steps aredetailedbelow:

NEARTERM(2016–2020):Bytheendofthenearterm,theNASwillremainresilientwithPBNservicesthroughoutClassAairspaceprovidedbyphasing inDMERNAVcoveragedownto18,000 feetabovemeansea level (MSL).TheexceptionisareasintheWesternMountainousRegion,whereterrainseverelylimitsline-of-sightcoverageataltitudesbelow24,000feetMSL.DMEcoveragewillexistwithouttheneedforanIRU,thoughoperatorswithoutIRUmayneedtoconfirmcriticalDMEsarenotoutofserviceintheterminalarea.ClassAairspacewillrequireDME/DMEpositioningforoperatorsneedingtoaccesstheairspaceduringaGNSSservicedisruption.OperatorsequippedwithonlyasingleFMS,andthusonlyasingleDME/DMEnavigationsource,willbeallowedtouseVOR(non-RNAV)orTacticalAirNavigationasanauthorizedsecondformofnavigationtocontinuetodispatchduringthedisruption.[...]

• Increasing situational awareness of GNSS disruption events and the ability to quicklycommunicateinformationtotheaffectedpartiesisanessentialcapabilityneededthroughouttheNAStoensureeffectiveandtimelyuseofresilientinfrastructure.Inthenearterm,theFAAwilldefinerequirementsforaSatelliteOperationsCoordinationConcept(SOCC)positionattheFAA’sAirTrafficControlSystemCommandCentertomanagerealtimeinformationontheNASnavigationstatus.

MIDTERM(2021-2025)Bytheendofthemid-term,theresilienceoftheNASwillbeincreasedfurtherwiththefollowingFAAcommitments:

• DME/DMEcoverage,providingRNAV1navigation,will beextendeddown toNSG1and2airports to facilitate a conventional approach, as required (for example, 1,500 feet heightaboveairport).ThiscoveragewillrequiretheinstallationofadditionalDMEfacilities.Notethatfordepartures,DME/DMEmaynotprovideneededcoveragetosupportallPBNdeparturesdue



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totheaircraftcomputerprocessingdelaythatexistsafterreceivingDMEgroundtranspondersignals.TomaintainacceptabledepartureoperationsduringaGNSSdisruption,localfacilitieswill have to develop contingency plans. DME/DME equipment will be required for thoseoperatorsneedingtoaccesstheairspaceduringaGNSSservicedisruption;and

• TheSOCCwillbeginoperationsinthemid-term,providingthereal-time,system-levelviewofNASnavigationresiliencyandcoordinatingmitigationtoservicedisruptions.

TheprovisionofDME/DMERNAVcoverageinClassAairspace intheneartermandattheselectedairportsduringthemidtermwillconstitutearesilientpositionandnavigationservicefortheNAS.TheFAAwillcontinuetoevaluatealternativesforpositionandnavigationastechnologiesandcapabilitiesadvance.FARTERM(2026–2030)Inthefarterm,theFAAwillfocusonthecompletionoflegacyinfrastructuredivestment,makingPBNthestandardmethodofnavigation.Conventionalnavigationwillexisttoensuretheresiliencyofnon-DME/DME operations, low-visibility approaches and DoD requirements. The FAA will be able tocompleteprogramstorecapitalizeanddivestfromadditionalground-basedinfrastructure.Prioritiesforthe2026–2030timeframeinclude:[…]

• ContinuingresearchintoAlternativePosition,NavigationandTiming(APNT)capabilities.

BEYOND2030As the near- andmid-term solutions are implemented, DME and VORwill serve into the far-termtimeframe.During the far termandmovingout into the2030 timeframeandbeyond, theFAAwillcontinuetoresearchthebestmethodsforAPNT[…]TheEuropeanA-PNTconceptisunderdefinitionbutislikelytohaveasimilarapproach.

One part of the SESARA-PNT study aimed at listing all the possible alternatives toGPS (future oralready existing) while the second part has been focusing on DME enhancement at ground or atairbornelevel.

ThefollowingisasummaryofthestudiedalternativetechnologiesandtheirapplicabilitytoNAVISASproject.

A-PNTTechnology

Concept Applicability

Generalaviation

Ultra-light UAV

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Enhanced DME-FMS

Existing on-board FMS andDME receiver alreadycompute a DME/DMEposition but do not provideintegrity. Updating the FMSsoftware with an integritycomputation capability(similar to the RAIMalgorithm)couldbesufficientto provide RNP 1 capabilitybasedonDMEonly. Furtherpopulating the current DMEnetwork will be needed toguarantee sufficientcoverage.

Notapplicable

DMEequipmentisrequired

Wide AreaMultilateration(WAM)

WAM is able to findaircraftpositions by time differenceof arrival measurementsbetween several groundstations. The system iscomposed by a number ofreceiver/interrogatorslocatedinpreciselysurveyedpositions, receiving modeA/C and Mode-S (and insome systems ADS-B also)replies.

Yes Yes if equippedwithtransponder

Yes if equippedwithtransponder

Mode-N Mode N system ischaracterized by groundstations (synchronized intime) that transmit on asingle frequency theircoordinates. These periodictransmissionsarereferredtoasModeNsquitter.

The main differencebetween DME and Mode Nusing is related to thenumber of useful groundstations: while DME islimited to a maximum offive sources per DMEinterrogator, a Mode Ntransceiver can utilize allMode N ground stations

Notapplicable

ModeNsquitterequipmentisrequired



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within radio line of sight.SoModeNfunctionofthetransceiver is able toestimate the aircraftposition from Mode Nsquittersofdifferentgroundstations using timedifferencesofarrival.

LDACS LDACS (L-band DigitalAeronauticalCommunication System) isthe future ground-basedcommunications link (960-1164 MHz) and is alreadyused by Aeronauticalnavigation services andAeronautical militarycommunicationssystems.

Tocalculatecorrectairborneposition, it is necessary tomultilaterate the receivedsignals from at least fourgroundtransmitters.

Notapplicable

LDACSequipmentisrequired

MosaicDME This solution consists of asingle conventional DMEtransponder and multiplepseudolites installed in thesame location. The DMEtransponder operatesaccording to the currentstandards on the basis of atwo-way ranging principle,while the pseudolitesbroadcast one-waycontinuoussignalsforcarrierphasemeasurements.

Notapplicable

DMEequipmentisrequired

eLORAN Loran (LOng RAngeNavigation) is a ground-based radio-navigationsystem that preceded

Notapplicable

LORANequipmentisrequired

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satellite navigation. Loran isbased on the broadcast ofextremelyhighpowersignalsinthelowfrequencyportionof the radio spectrum(operating between 90 kHzand110kHz).

An updated LORAN version(called Enhanced LORAN)provideschanges to the lastLORAN system to improveaccuracy, reliability,integrity, service availabilityand robustness against theinterference.

Table4–SummaryofalternateA-PNTtechnologies



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StateoftheArtreviewonclocksandatomicgyroscopes

Here,aStateoftheArt(SoA)analysisonbothminiatureatomicgyroscopes(MAG)andatomicclocks(MAC) is presented with key performances, limitations and advantages compared with existingsolutionsforAPNTIMUsandGNSS,respectively.

3.1 Miniatureatomicclocks

3.1.1 Introduction

Thecapabilitytomaintainaccuratetimingoverextendedperiodoftimewithcompactandlowpowerconsumptiondevicesisakeybenefitforanumberofapplications.

InGNSS,frequencyspectrumcongestiongeneratesinterferencesthatrepresentakeychallengeforserviceintegrityandpersistence.Thankstoitssuperiortimingaccuracyoverextendedperiodoftime,miniatureatomicclocksguarantee fast re-acquisitionof thesignaland longcoherence integration,thereby improving service availability in adverse environment (provided the actual location isestimatedfrominertialnavigation).Whilethisisofobviousbenefitforhigh-endGNSSuserterminals,itisalsoofhighinterestforon-boardGNSSreceiversthatarebeingincreasinglyusedforgeostationarysatellitestationkeeping,especiallyinthehighlyoccupiedorbitalslots.

AnumberofEarthobservationinstruments(radiometers,GNSSradiooccultation…)operatinginnon-coherentmodecould significantly improve their sensitivityand resolutionby integrating the signaloverlongerperiodoftime.Thankstoitscompactformfactorandlowpowerconsumption,aminiatureatomicclock(MAC)couldbedirectlyintegratedintheinstrumentandwouldnotrequirepower-hungryandbulkyreferenceoscillator.

ThereishowevernoMACtechnologyavailableinEurope,thesoleworldwidesupplierbeingintheUS(MicrosemiCorporation).Whileoverthe lastdecade,someeffortshavebeendedicatedworldwideandalsoinEuropetothedevelopmentofMACsatthesystemlevel,thereiscurrentlyalackofactivitydedicatedtoahigh-performingphysicspackage.

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3.1.2 Workingprinciples

Aminiatureatomicclock(MAC)isanoscillatorprovidingasignalwithexquisitefrequencyandhencetiming stability. This frequency stability is derived from the intrinsically stable frequency of atoms(RubidiumorCesiumatomsforaMAC).AMACisbasicallyaquartzlocaloscillatorthatisfrequencylockedtoanatomicreferencetransition(so-calledpassiveatomicclock).Thegaseousphasereferenceatomsareenclosedinavaporcell.Inordertoaccessthehyperfineatomicreferencetransitionwhichisate.g.6.8GHzfortheisotope87ofRubidium,avertical-cavitysemiconductorlaser(VCSEL)hasitsinjectioncurrentmodulatedathalftheatomichyperfinefrequencyinordertogeneratesidebandsinwhichareresonantwiththeatomichyperfinefrequency,whilethewavelengthofthelaserisstabilizedtooneopticalatomicabsorptionline(typicallyat795nm).Intheseconditionsthereisaslightincreaseofthelighttransmissionthroughtheatomicvaporcell.ThiseffectcalledCoherentPopulationTrapping(CPT)isattheheartofaMAC.

AtypicalMACarchitectureisdisplayedinFigure11.Thephysicspackage(PP)iscentraltotheclockandcontainstheMEMSatomicvaporcell,theVCSEL,somemicro-opticstopreparethelightemittedbythelaserthatinteractswiththeatoms,heatersandtemperaturesensorsfortheMEMScellandtheVCSEL,coils togenerateastraightmagnetic field (B field) for theatoms,andaphotodiode (PD) todetecttheatomicsignals.ThePPisdrivenwithelectronicsthathastoprovideDCinjectioncurrenttotheVCSEL,controlloopfortheVCSELtemperature,controllooptostabilizetheVCSELwavelengthonan atomic optical transition (laser lock), anRF synthesizer to generate the appropriatemicrowavesignalusedtointerrogatetheatomichyperfinefrequencyviathelaserandphaselockedloop(PLL)tophaselocktheclocklocaloscillator(typicallya10-MHzquartzoscillator).NotshowninFigure11butnecessarytocontrolthefullclock isamicrocontroller.Alsonotrepresented isamagneticshield inordertoisolatetheatomsfromexternalmagneticfields.



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Figure11.BlocdiagramofaMAC(i.e.apassiveatomicclock)

3.1.3 Challenges

InordertomakeaMACcompetitive,theperformanceintermsoffrequencystabilityisessentialbuttheformfactorandthecostsareofkeyimportanceaswell.ThePPisacriticalelementneededtofulfillthesechallengesandsofarnosolutionexiststhatishighperformingandcompetitiveincost.

Theformfactoroftoday’sprototypesiscubicsincethedifferentknownPPsarerealizedwithastackofthecomponents.RecentR&Dactivitiestowardsaflatdesignareundertaken,e.g.atCSEM.

ThepowerconsumptionofthePPisessentiallydrivenbythelaserandcellthermalmanagementwithtemperatures in the order of 80°C. Careful thermalmanagement and hermetically sealed vacuumencapsulation are essential at laser-package and cell-package interfaces to ensure high thermalresistivityandthusalsoimprovethermalstability.

TheproductioncostofthePPisstronglydependentonthepackagingtechnique(assemblyprocess)and the technology selected for thepackage itself.Apart from thecost, yieldand reli

Documents

Building Blocks for Small Aircraft APNT · building blocks for small aircraft APNT (Months: 3-10) of NAVISAS. It provides an overview of the state of the art of navigation techniques