2009 International Symposium on GPS/GNSS

Effect of Quasi Zenith Satellite (QZS) on Q (Q )GPS Positioning

Tokyo University of Marine Science and Technology

T. Takasu, T. Ebinuma and A. Yasuda

QZSS (1)QZSS (1)

• QZSS (Quasi‐Zenith Satellite System)– Regional space‐based PNT system around Japan– First satellite launch: 2010 summer– 3‐satellites in Phase 2– Interoperability with GPS

• Satellite Orbit Characteristics– IGSO (Inclined Geostationary Orbit) with slight eccentricity– 8 shape of satellite ground trackp g– At least 1 satellite at higher‐elev. angle than 70˚ at Tokyo– Effective in urban canyon or at mountainous locationEffective in urban canyon or at mountainous location

2

QZSS (2)QZSS (2)

• Expected Effects of QZSS on GPS Positioning– Improved satellite availabilityp y– Improved satellite geometry (DOP) especially on limited sky‐view conditionlimited sky view condition

– Improved accuracy for single point positioningd i bi i l i f– Improved integer ambiguity resolution for RTK 

with triple‐frequency signals (L1+L2+L5)

• DGPS corrections provided by QZSSOut of scope of this study

3

Out of scope of this study

Satellite ConstellationSatellite Constellation• 3 QZSs: 3 IGSO• 3 QZSs: 3 IGSO• 7 QZSs: 3 IGSO + 4 GEO (Future Enhancement)

Sat OrbitOrbit Element

a e i Center 

Ground Tracks Orbit Elements

(km) e (˚) Long.QZS1 IGSO 42164 0.075 43.0 130˚E

QZS2 IGSO 42164 0 075 43 0 135˚EQZS2 IGSO 42164 0.075 43.0 135 E

QZS3 IGSO 42164 0.075 43.0 140˚E

QZS4 GEO 42164 0.0 0.0 78˚E

QZS5 GEO 42164 0.0 0.0 116˚E

QZS6 GEO 42164 0.0 0.0 154˚E

4

QZS7 GEO 42164 0.0 0.0 168˚W

Evaluation MethodEvaluation Method

• Software Simulator– Simulated (QZSS) and real (GPS) ephemerides(Q ) ( ) p– Various error modelsOutputs RINEX OBS including GPS and QZSS data– Outputs RINEX OBS including GPS and QZSS data

• Post processing analysis– Inputs RINEX OBS/NAV file– Analysis of satellite visibility DOP etcAnalysis of satellite visibility, DOP etc. – Various positioning modes and options

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Software SimulatorSoftware Simulator

GPS+QZSSTropos.M d l

Multipath/R N i

Receiver Cl k BiGPS

SimulatedPseudorange/Carrier‐phase

Model Rcv NoiseClock‐BiasGPS Ephemeris

Sat Pos /Clock

Range+ Clocks

p

RINEXNAV

RINEXfor

QZSS Simulated

RINEXOBS

for phase

Receiver FOV Ionos PhaseOrbitSimulated Ephemeris

Receiver Position

FOVModel

Ionos.Model

PhaseBias

OrbitError

6

FOV Mask ModelFOV Mask Model

• Simulation of typical urban canyon environment• Limited sky‐view by surrounding obstacles

GPS and QZSSGPS and QZSS satellite tracks

7

Sky‐view by fish‐eye lens FOV mask areas

Post Processing AnalysisPost Processing Analysis

• RTKLIB ver. 2.3.0b– Analysis of solution availability and DOPy y– Single point positioningCarrier based relative positioning to simulate RTK– Carrier‐based relative positioning to simulate RTK

– Enhancement to support QZSS RINEX OBS/NAVGPS+QZSS

RINEX NAV/OBS SolutionFile

SoftwareSimulator RTKPLOTRTKPOST

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Sky PlotsSky‐Plots

Beijing Seoul Tokyo

: GPS

: QZSS

9ShanghaiBangkok

Satellite VisibilitySatellite VisibilityAt Tokyo with FOV mask

GPSGPS(PRN)

QZS1‐34 7

10

4‐7

PDOPPDOPAt Tokyo with FOV mask

GPS Only

Average: 4.6 

GPS Only

Average: 4.4

GPS+3 QZSs

Average: 3.5g

GPS+7 QZSs

11: # of Sats<4

Solution Availability and PDOPSolution Availability and PDOPGPS O l GPS 3 QZS GPS 7 QZS

SiteGPS Only GPS+3 QZSs GPS+7 QZSs

Ratio* Average PDOP Ratio* Average 

PDOP Ratio* Average PDOPPDOP PDOP PDOP

Tokyo 82.2% 4.6 98.1% 4.4 99.2% 3.5

Seoul 75.7% 4.9 98.5% 4.2 100% 3.3

Beijing 83 5% 5 5 96 6% 4 2 100% 2 9Beijing 83.5% 5.5 96.6% 4.2 100% 2.9

Shanghai 78.6% 5.2 95.3% 4.1 100% 2.3g

Bangkok 90.3% 4.5 98.8% 3.2 100% 2.5

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* Raito of epochs with proper positioning solutions

Single Point PositioningSingle Point Positioning

• Positioning Options– Mode: Single point positioningg p p g– GPS+QZSS, L1 C/A, pseudorangeElevation mask: 15˚– Elevation mask: 15

– Ionosphere correction: Klobuchar model– Troposphere correction: Saastamoinen model– No DGPS correction

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Solutions of Single Point PosSolutions of Single Point Pos.At Tokyo with FOV mask

GPS Only GPS+3 QZSs GPS+7 QZSs

RMSEE: 6.2mN: 8.2m

RMSEE: 2.0mN: 1.5m

RMSEE: 2.1mN: 1.3m

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U: 15.2m U: 4.3m U: 3.7m

Accuracy of Single Point PosAccuracy of Single Point Pos.RMS Errors (m)

SiteGPS Only GPS+3 QZSs GPS+7 QZSs

( )

EW NS UD EW NS UD EW NS UD

Tokyo 6.2 8.1 15.2 2.0 1.5 4.3 2.1 1.3 3.7y

Seoul 5.0 5.4 17.5 1.8 1.4 4.1 1.8 1.4 4.1

Beijing 5.7 5.4 11.1 1.3 1.3 3.1 1.4 2.0 3.6

Shanghai 3.5 3.2 8.3 2.8 2.4 6.0 1.1 1.4 2.8

Bangkok 1 8 2 0 6 8 1 2 1 8 3 6 1 2 0 7 5 0

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Bangkok 1.8 2.0 6.8 1.2 1.8 3.6 1.2 0.7 5.0

RTK PositioningRTK Positioning

• Positioning Options– Mode: Kinematic– GPS+QZSS, L1+L2+L5, pseudorange+carrier‐phase (assume only 4 GPS satellites support L5)(assume only 4 GPS satellites support L5)

– Elevation mask: 15˚h / h i– Ionosphere/troposphere correction: None

– Integer ambiguity resolution: LAMBDA (thres.=3)

• Baseline Length: 10 kmRover relative position with refer to base station– Rover relative position with refer to base‐station

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Solutions of RTK PositioningSolutions of RTK PositioningAt Tokyo with FOV mask

GPS Only GPS+3 QZSs GPS+7 QZSs

RMSE of Fixed Sol.E: 1.6cmN: 3.0cm

RMSE of Fixed Sol.E: 0.6cmN: 1.2cm

RMSE of Fixed SolE: 0.6cmN: 1.2cm

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U: 3.1cm U: 1.5cm U: 1.2cm: Fixed Solution : Float Solution

Accuracy of RTK PositioningAccuracy of RTK PositioningFixing Ratio and RMS Errors (cm) of Fixed Sol.

SiteGPS Only GPS+3 QZSs GPS+7 QZSsFixing Ratio Fixing Ratio Fixing Ratio

EW NS UD EW NS UD EW NS UDEW NS UD EW NS UD EW NS UD

Tokyo 84.2% 97.5% 98.5%1.6 3.0 3.1 0.6 1.2 1.5 0.6 1.2 1.2

Seoul 76.0% 98.6% 99.1%0.9 2.0 3.3 0.6 1.4 1.7 0.5 1.4 1.0

86 4% 95 6% 98 8%Beijing 86.4% 95.6% 98.8%1.2 2.0 2.9 0.4 1.6 1.2 0.3 1.5 1.0

76 7% 98 5% 98 2%Shanghai 76.7% 98.5% 98.2%0.9 1.9 2.3 0.5 1.5 1.0 0.2 1.4 0.7

B k k 83.5% 95.6% 96.4%

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Bangkok 0.8 2.7 2.1 0.4 2.6 1.8 0.2 2.5 1.3

ConclusionsConclusions

• Evaluation of the effects of QZSS on GPS positioning– More than 95% of solution availability with QZSS even on limited sky‐view condition

– More accurate single point solution primary due to DOP i t ith QZSSimprovement with QZSS 

– More than 90% of fixing ratio is expected for RTK with QZSS and triple frequency signalsQZSS and triple‐frequency signals

• QZSS combined with GPS will much enhance the iti i f i ll ipositioning performance especially in sever 

environment like urban canyon.

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A diAppendix

20

Satellite Visibility at SeoulAt Seoul with FOV mask

Satellite Visibility at Seoul

GPSGPS(PRN)

QZS1‐34 7

21

4‐7

PDOP at SeoulPDOP at SeoulAt Seoul with FOV mask

Average: 4.6 

GPS Only

Average: 4.9 

GPS Only

Average: 4.4

GPS+3 QZSs

Average: 4.2 

Average: 3.5Average: 3 3g

GPS+7 QZSsAverage: 3.3

2222: # of Sats<4