Tokyo University of Marine Science and Technology

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Effect of Quasi Zenith Satellite (QZS) on GPS
Positioning
2009 International Symposium on GPS/GNSS

• Tokyo University of Marine Science and Technology
• T. Takasu, T. Ebinuma and A. Yasuda

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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 track
• At least 1 satellite at higher-elev. angle than
  70 at Tokyo
• Effective in urban canyon or at mountainous
  location

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QZSS (2)

• Expected Effects of QZSS on GPS Positioning
• Improved satellite availability
• Improved satellite geometry (DOP) especially on
  limited sky-view condition
• Improved accuracy for single point positioning
• Improved integer ambiguity resolution for RTK
  with triple-frequency signals (L1L2L5)
• DGPS corrections provided by QZSS

Out of scope of this study
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Satellite Constellation

• 3 QZSs 3 IGSO
• 7 QZSs 3 IGSO 4 GEO (Future Enhancement)

Ground Tracks
Orbit Elements
Sat Orbit Orbit Element Orbit Element Orbit Element Orbit Element
Sat Orbit a (km) e i () Center Long.
QZS1 IGSO 42164 0.075 43.0 130E
QZS2 IGSO 42164 0.075 43.0 135E
QZS3 IGSO 42164 0.075 43.0 140E
QZS4 GEO 42164 0.0 0.0 78E
QZS5 GEO 42164 0.0 0.0 116E
QZS6 GEO 42164 0.0 0.0 154E
QZS7 GEO 42164 0.0 0.0 168W
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Evaluation Method

• Software Simulator
• Simulated (QZSS) and real (GPS) ephemerides
• Various error models
• Outputs RINEX OBS including GPS and QZSS data
• Post processing analysis
• Inputs RINEX OBS/NAV file
• Analysis of satellite visibility, DOP etc.
• Various positioning modes and options

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Software Simulator
Tropos. Model
Multipath/ Rcv Noise
Receiver Clock-Bias
GPSQZSS Simulated Pseudorange/ Carrier-phase
GPS Ephemeris
Sat Pos /Clock
Range Clocks
RINEX NAV
for phase
RINEX OBS
QZSS Simulated Ephemeris
Receiver Position
FOV Model
Ionos. Model
Phase Bias
Orbit Error
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FOV Mask Model

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

GPS and QZSS satellite tracks
Sky-view by fish-eye lens
FOV mask areas
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Post Processing Analysis

• RTKLIB ver. 2.3.0b
• Analysis of solution availability and DOP
• Single point positioning
• Carrier-based relative positioning to simulate
  RTK
• Enhancement to support QZSS RINEX OBS/NAV

GPSQZSS RINEX NAV/OBS
Solution File
RTKPLOT
RTKPOST
Software Simulator
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Sky-Plots
Beijing
Seoul
Tokyo
GPS
QZSS
Shanghai
Bangkok
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Satellite Visibility
At Tokyo with FOV mask
GPS (PRN)
1-3
QZS
4-7
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PDOP
At Tokyo with FOV mask
Average 4.6
GPS Only
Average 4.4
GPS3 QZSs
Average 3.5
GPS7 QZSs
of Satslt4
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Solution Availability and PDOP
Site GPS Only GPS Only GPS3 QZSs GPS3 QZSs GPS7 QZSs GPS7 QZSs
Site Ratio Average PDOP Ratio Average PDOP Ratio Average 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 2.9
Shanghai 78.6 5.2 95.3 4.1 100 2.3
Bangkok 90.3 4.5 98.8 3.2 100 2.5
Raito of epochs with proper positioning
solutions
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Single Point Positioning

• Positioning Options
• Mode Single point positioning
• GPSQZSS, L1 C/A, pseudorange
• Elevation mask 15
• Ionosphere correction Klobuchar model
• Troposphere correction Saastamoinen model
• No DGPS correction

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Solutions of Single Point Pos.
At Tokyo with FOV mask
GPS Only
GPS3 QZSs
GPS7 QZSs
RMSE E 2.0m N 1.5m U 4.3m
RMSE E 2.1m N 1.3m U 3.7m
RMSE E 6.2m N 8.2m U 15.2m
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Accuracy of Single Point Pos.
RMS Errors (m)
Site GPS Only GPS Only GPS Only GPS3 QZSs GPS3 QZSs GPS3 QZSs GPS7 QZSs GPS7 QZSs GPS7 QZSs
Site 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 3.7
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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RTK Positioning

• Positioning Options
• Mode Kinematic
• GPSQZSS, L1L2L5, pseudorangecarrier-phase
  (assume only 4 GPS satellites support L5)
• Elevation mask 15
• Ionosphere/troposphere correction None
• Integer ambiguity resolution LAMBDA (thres.3)
• Baseline Length 10 km
• Rover relative position with refer to
  base-station

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Solutions of RTK Positioning
At Tokyo with FOV mask
GPS Only
GPS3 QZSs
GPS7 QZSs
RMSE of Fixed Sol. E 0.6cm N 1.2cm U 1.5cm
RMSE of Fixed Sol E 0.6cm N 1.2cm U 1.2cm
RMSE of Fixed Sol. E 1.6cm N 3.0cm U 3.1cm
Fixed Solution
Float Solution
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Accuracy of RTK Positioning
Fixing Ratio and RMS Errors (cm) of Fixed Sol.
Site GPS Only GPS Only GPS Only GPS3 QZSs GPS3 QZSs GPS3 QZSs GPS7 QZSs GPS7 QZSs GPS7 QZSs
Site Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio Fixing Ratio
Site EW NS UD EW NS UD EW NS UD
Tokyo 84.2 84.2 84.2 97.5 97.5 97.5 98.5 98.5 98.5
Tokyo 1.6 3.0 3.1 0.6 1.2 1.5 0.6 1.2 1.2
Seoul 76.0 76.0 76.0 98.6 98.6 98.6 99.1 99.1 99.1
Seoul 0.9 2.0 3.3 0.6 1.4 1.7 0.5 1.4 1.0
Beijing 86.4 86.4 86.4 95.6 95.6 95.6 98.8 98.8 98.8
Beijing 1.2 2.0 2.9 0.4 1.6 1.2 0.3 1.5 1.0
Shanghai 76.7 76.7 76.7 98.5 98.5 98.5 98.2 98.2 98.2
Shanghai 0.9 1.9 2.3 0.5 1.5 1.0 0.2 1.4 0.7
Bangkok 83.5 83.5 83.5 95.6 95.6 95.6 96.4 96.4 96.4
Bangkok 0.8 2.7 2.1 0.4 2.6 1.8 0.2 2.5 1.3
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Conclusions

• 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 improvement with QZSS
• More than 90 of fixing ratio is expected for RTK
  with QZSS and triple-frequency signals
• QZSS combined with GPS will much enhance the
  positioning performance especially in sever
  environment like urban canyon.

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Appendix
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Satellite Visibility at Seoul
At Seoul with FOV mask
GPS (PRN)
1-3
QZS
4-7
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PDOP at Seoul
At Seoul with FOV mask
Average 4.9
Average 4.6
GPS Only
Average 4.4
Average 4.2
GPS3 QZSs
Average 3.5
Average 3.3
GPS7 QZSs
of Satslt4
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