Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J Manoj Deo & A/Prof Ahmed El-Mowafy Triple Frequency precise point positioning with multi-constellation GNSS International Global Navigation Satellite Systems Conference 6-8 December 2016 Department of Spatial Sciences
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Triple Frequency precise point positioning with multi ... · Multi-constellation Biases • Inter-System Time Bias (ISTB ): due to each constellation having own timescales. Accounted
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Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Manoj Deo & A/Prof Ahmed El-Mowafy
Triple Frequency precise point positioning with multi-constellation GNSS
International Global Navigation Satellite Systems Conference
6-8 December 2016
Department of Spatial Sciences
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Outline
Introduction to Multi-Frequency Multi-constellation (MFMC) PPP
Modelling of Biases • Single constellation biases • Multi-constellation biases
Triple Frequency PPP Models • Functional and Stochastic
Validation and Testing • Test data, analysis results • GPS+Beidou+Galileo
Conclusions and future work
1
International Global Navigation Satellite Systems Conference, 6-8 December 2016
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Introduction to PPP PPP originally presented by Zumberge et al. 1997
• Dual frequency, single constellation model • Widely used for real-time applications e.g. mining, agriculture, construction
surveying • Drawback: requires float Ambiguity Convergence of typically 30min • Various enhancements introduced over the years, e.g. PPP-AR.
Convergence time remains an issue
This Contribution: Use MFMC (>2 freq.) data to develop enhanced PPP models with reduced convergence time
Focus on float ambiguity convergence • PPP-AR considered in future research
Novel triple frequency linear combinations
Compare and evaluate performance
2
International Global Navigation Satellite Systems Conference, 6-8 December 2016
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Modelling of Biases Models for cm-mm level errors: solid earth tide, ocean tide,
atmospheric loading, phase wind-up, satellite antenna phase centre offset, relativity.
Troposphere: model hydrostatic and estimate wet component
Ionosphere: form iono-free combinations or estimate with multi-frequency data
Single Constellation Biases • Satellite and receiver hardware biases: affects phase and code. Digital
delays in the signal generator, signal distortion, etc. Removed at receiver end by BSSD. Satellite end stable over typical PPP session
• Differential Code Biases (DCB): differences in hardware bias due to frequency difference. Not required if using iono-free combination of ‘reference signals’
3 International Global Navigation Satellite Systems Conference, 6-8 December 2016
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Modelling of Biases Single Constellation Biases…
• Initial Fractional Phase Bias (IFPB): exist in satellite and receiver and <1cycle. Constant for each session; reset when receiver is switched off and on. Removed at receiver end by BSSD
• Differential Phase Biases (DPB): due to phase hardware bias differing for each frequency. Inseparable from IFPB, combined as one term.
• Lumped with non-integer carrier phase ambiguity term. PPP-AR requires accurate calibration.
Multi-constellation Biases • Inter-System Time Bias (ISTB): due to each constellation having own timescales.
Accounted for by: 1. estimating a separate bias for each system, or 2. estimating the bias for one system and then estimating the differences for other
systems with reference to this system • Inter System Biases (ISB): Due to signals from different constellations having different
hardware biases (even though having same frequency). • Estimate as a parameter or BSSD within same constellation.
4
International Global Navigation Satellite Systems Conference, 6-8 December 2016
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Triple Frequency PPP Model 1
5 International Global Navigation Satellite Systems Conference, 6-8 December 2016
Triple frequency phase-only and code-only linear combination
Coefficients for triple-frequency linear combinations for different GNSS constellations and signals. Percentage change in noise compared to dual-frequency ‘reference signals’. For GLONASS K2, the L1/L2 CDMA assumed as the reference signals.
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Refined Dual Frequency Mixed code-carrier linear combination
• Same properties as model 1 (iono-free, low noise, geometry preserving) • Use two proposed combinations, with dual frequency iono-free phase
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
PPP with individual uncombined signals • Use raw phase and code measurements without linear combinations • Each satellite introduces 6 measurements (3 code and 3 phase) • Use extra measurements to solve for the ionosphere error • Perform between satellite single differencing (BSSD) to eliminate
receiver biases
𝑃1 = 𝜌 + 𝐼 + 𝑇 + 𝜀𝑃1
𝑃2 = 𝜌 + 𝑖12
𝑖22𝐼 + 𝑇 + 𝜀𝑃2
𝑃5 = 𝜌 + 𝑖12
𝑖52𝐼 + 𝑇 + 𝜀𝑃5
𝜙1 = 𝜌 − 𝐼 + 𝜆1𝑁1∗ + 𝑇 + 𝜀𝜙1
𝜙2 = 𝜌 − 𝑖12
𝑖22𝐼 + 𝜆2𝑁2∗ + 𝑇 + 𝜀𝜙2
𝜙5 = 𝜌 − 𝑖12
𝑖52𝐼 + 𝜆5𝑁5∗ + 𝑇 + 𝜀𝜙5
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Triple Frequency PPP Model 3
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• Test data simulated for Hobart (HOB2), Alice Springs (ALIC), Yarragadee (YAR2) and Townsville (TOW2)
• Model 1 tested • Triple frequency phase-only and code-only linear combination • GPS (G), Beidou (C) and Galileo (E)
• Performance testing • Convergence: Time to attain and maintain 3-dimensional accuracy of 5cm • Precision: std. Accuracy: RMSE after convergence • Compare standard dual frequency model with triple frequency G, G+C,
G+C+E
• Analyse hourly blocks of 1-days data that converged
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Validation and Testing
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Dual Freq. G
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Results - ALIC
Triple Freq. G
Triple Freq. G+C
Triple Freq. G+C+E
Triple freq. G+C best performance with improvement of 5mm in RMSE East and 5.7 minutes in convergence time
Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J
Dual Freq. G
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Results – HOB2
Triple Freq. G
Triple Freq. G+C
Triple Freq. G+C+E
Triple freq. G+C+E best performance with improvement of 4mm in RMSE up and 7.4 minutes in convergence time
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Dual Freq. G
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Results – TOW2
Triple Freq. G
Triple Freq. G+C
Triple Freq. G+C+E
Triple freq. G+C+E best performance with improvement of 4mm in RMSE up and 7.7 minutes in convergence time
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Dual Freq. G
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16
Results – YAR2
Triple Freq. G
Triple Freq. G+C
Triple Freq. G+C+E
Triple freq. G+C+E best performance with improvement of 11.5 minutes in convergence time. No noticeable improvement in accuracy
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Mean RMSE and convergence times with hourly blocks of data for the standard dual-frequency GPS only solution (L1-L2 G) and the triple frequency solutions for GPS only, GPS+Beidou (G+C) and GPS+Beidou+Galileo (G+C+E)
Department of Spatial Sciences - Ph.D. seminar, Manoj Deo April 16