PerformanceAnalysisofQZSSCentimeterLevelAugmentationServices(CLAS)ForStanfordPNT2019,Stanford,California

Po-ChunChiu,Shuo-JuYehandShau-ShiunJan

2019/10/29

InstituteofAeronauticsandAstronautics,NationalChengKungUniversity,Taiwan.

Outline

•  Quasi–ZenithSatelliteSystem•  MotivationsandObjectives•  CentimeterLevelAugmentationService•  L6DMessageStructure•  SubtypesinL6Message

•  CLASMessageAnalysis•  CLASAidingPrecisePointPositioning•  Conclusions•  FutureWork

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Quasi–ZenithSatelliteSystem(QZSS)

•  RegionNavigationSatelliteSystem•  1geostationaryequatorialorbit(GEO)satelliteand3Quasi-Zenithorbit(QZO)satellitesareincludedinQZSS.

•  EastAsiaandAustraliaarea•  L1,L2,L5,L6Signal•  CentimeterLevelAugmentationService(CLAS)

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CentimeterLevelAugmentationService

•  CLASsupportsRTK-PPPrealtimeusers.Itisdesignedtoimprovepositioningtocentimeterlevel.

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ObservationNetworks&Station

AugmentationDataGeneration&Transition

QZSSSatellite

L6Signal

LandSurvey ITConstruction ITAgriculture

Observation Space Representation (OSR)

State Space Representation (SSR)

Motivations

•  QZSSsignalcanbereceivedinTaiwananytimeinadayandhasaverygoodperformanceinelevation.

•  Theelevationofeachsatelliteisabove60°for12hoursperday.

5 Takeyasu Sakai & Satoshi Kogure (2018, September) QZSS Update. ION2018+, Miami, Florida

Taiwan

Objectives

•  TaiwanlocatesattheedgeofCLASserviceboundary.

•  ApreliminaryevaluationsofthePPPmethodwithCLASserviceareprovided.

•  SatelliteDatafromIGSstationandCLASdatafromQZSSwebsiteareused.

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L6DMessageStructure

•  L6DMessageStructure•  2000bps•  6subframesin30seconds•  Eachsubframetakes5seconds

Header49bits

Reed-SolomonCode256bits

DataPart1695bits

2000bits/sec

SubtypeN1 n1bits

SubtypeN2 n2bits

SubtypeNk nkbits

Header Reed-SolomonCodeDataPart5

5DataPartsin1Subframes

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…

…

Header Reed-SolomonCodeDataPart1

2000bits

L6DMessageStructure

•  Correctionscontainedin11Subtypeswillbetransmittedin6subframes.

•  NetworkIDisusedtoidentifyspecificlocalcorrectionmessages.

Subframe 1 2 3 4 5 6

Subtype 1~9,11 3,6,8,9,11 3,6,8,9,11 3,6,8,9,11 3,6,8,9,11 3,6,8,9,11

NetworkID

12,2 3,4,14 5,6,15,16 7,8,17,18 9,10,19 11,1

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CLASNetwork

•  Formedby19Networks.•  EachNetworkisformedbyseveralgridpoints.Thereare231gridpointsintotal.Gridpointsindicatethepositionofaobservationstation.

•  Thesestationsaresettocollectlocaldataandreportresultforfurtheraugmentationproduction.

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12

345 6 7

8

9

10

11

12

13

15 16 17 18

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SubtypesinL6Message

•  Subtype1:ThissubtypeindicatestheincludedsatellitesandsignalsintheCLASmessage.

•  Network-independentSubtype:Subtype2,3,4,5,7•  Onlytheinformationfromsubtype1isusedtodecodethesesubtypes.

MessageHeader CellMaskSatelliteMask SignalMask

MessageHeader

DataforSatellite/Signal1

DataforSatellite/SignalN

…

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SubtypesinL6Message

•  Network-DependentSubtype:Subtype6,8,9,11•  Dateincludeinthesesubtypeswillincrease/decreasewiththequantityofgridpointsineachNetwork.

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MessageHeader

Grid1dataforSatellite1

Grid𝑁datafordataforSatellite1

Grid1dataforSatellite𝑀

Grid𝑁datafordataforSatellite𝑀

…

…

…

NetworkID

CorrectionsinL6Message

SubtypeCorrection

1 2 3 4 5 6 7 8 9 10 11

CellMask √

OrbitCorrection √ ●

GNSSClockCorrection √ ●

Code/PhaseBias √ √ ●

IonosphereSlantDelay ● ●

TroposphereDelay ●

Integrity √

TBD * 12

√ forGeneralData,30secondsinterval; ● forNetworkData,5secondsinterval

AvailabilityofCLAS

•  Date:2018/11/28•  Time:0:00~23:59•  DataSize:164.8MB•  Location:Nakatane,Japan

•  Atleast6GPSSatellitesaresupportedin95%ofaday.

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OrbitCorrection

•  Source:Subtype2,11•  Date:2018/11/28•  Satellite:G06•  UserAlgorithm: 𝑟↓𝑐𝑜𝑟𝑟𝑒𝑐𝑡 = 𝑟↓𝑒𝑝ℎ −𝛿𝑟↓𝐶𝐿𝐴𝑆  •  Radial,Cross,andAlongvectorsagainstuserpositionwillhelpcalculation.

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NoCLASSupportforthisSatellite

GNSSClockCorrection

•  Source:Subtype3,11•  Date:2018/11/28•  Satellite:G06•  UserAlgorithm: 𝑡↓𝑐𝑜𝑟𝑟𝑒𝑐𝑡 = 𝑡↓𝑏𝑟𝑜𝑎𝑑𝑐𝑎𝑠𝑡 −𝛿𝑡↓𝐶𝐿𝐴𝑆 

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GNSSCode/PhaseBias

•  Source:Subtype4,5,6•  Date:2018/11/28•  Satellite:G06•  UserAlgorithm: 𝜌↓𝑐𝑜𝑟𝑟𝑒𝑐𝑡,𝑐𝑜𝑑𝑒/𝑝ℎ𝑎𝑠𝑒 = 𝜌↓𝑐𝑜𝑑𝑒/𝑝ℎ𝑎𝑠𝑒 +𝛿𝜌↓𝐶𝐿𝐴𝑆,𝑐𝑜𝑑𝑒/𝑝ℎ𝑎𝑠𝑒 •  Mappingbytheline-of-sightvectorfromuserpositiontothesatellite

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IonosphereSlantDelayCorrection

•  Source:Subtype8,9•  Date:2018/11/28•  Polynomialpartandresidualpart

•  Ionosphereslantdelayatuserpositioniscomputedbyinterpolatingtheoneonreferencegrids.

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TroposphereDelayCorrection

•  Source:Subtype9•  Date:2018/11/28•  Troposphereverticaldelayvariationsarecomputedbyinterpolatingorextrapolatingthedataonthereferencegrid.

•  Amappingfunctionisnecessaryforfurtherapplication.

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CLASAidingPrecisePointPositioning

•  Date:2018/11/28•  Accuracylevel:1meter•  ConvergenceImprovement:901stepochto160thepoch

•  Reductionisabout83%originalneededepoch.

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901st 160th

CLASAidingPrecisePointPositioning Date:2018/11/28Accuracylevel:0.3meter

Date:2019/03/04Accuracylevel:0.3meter

1730th

867th

20

1293rd

582nd

Reduction:50%

Conclusions

•  CLASbinarydatadecoderconsideredasaSSRtoOSRconvertor.•  CLASuseralgorithmarecompletedandcanassistpositioningmethods.

•  CombinationofPPPandCLASisimplemented.•  ConvergencetimeimprovementagainstresultbeforeapplyingCLAS:•  About50%for0.3meteraccuracylevel•  About83%for1meteraccuracylevel

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FutureWork

•  UsingSoftware-DefinedReceiver(SDR),theQZSSL6canbeobtainedthroughacquisition,trackinganddemodulationprocess.WewillcompletetheworkandapplyCLASdatatolocalpositioning.

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Reference

•  Takeyasu Sakai & Satoshi Kogure (2018, September ). QZSS Update. ION2018+, Miami, Florida. Retrieved from https://www.ion.org/publications/abstract.cfm?articleID=15837

•  Cabinet Office(2018). Quasi-Zenith Satellite System Interface. Specification: Centimeter Level Augmentation Service. Retrieved from https://qzss.go.jp/en/technical/ps-is-qzss/ps-is-qzss.html

•  T. Takasu(2019). RTKlib(v2.4.3). Retrieved from http://www.rtklib.com/rtklib.htm

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ThankYou! Po-ChunChiu

NationalChengKungUniversitykenhiowatha@gmail.com