Ionospheric Scintillation Effects on GPS Pseudorange and Carrier Phase Measurements and an Adaptive Algorithm to Limit Position Errors during Scintillation

Greg Myer, Yu (Jade) Morton, Brian Schipper

Peer Reviewed

Abstract:	The ionosphere is an important cause of disturbances on GNSS signals, especially in high latitudes and equatorial areas [1][2]. Previous studies indicate that while ionospheric scintillation may cause abrupt, random fluctuations in carrier phase measurements [3], its impact on pseudorange is less serious [4][5]. Since modern GNSS receivers, especially those for high precision applications, use carrier phase corrected pseudoranges to improve PNT solution accuracy, there exists the need to have a better understanding of the scintillation effects on carrier phase measurements and developing means to mitigate scintillation induced errors in PNT solutions. In this paper we demonstrate how scintillation impacts carrier phase and pseudorange measurements using real scintillation data collected at low and high latitudes, and investigate how they affect PVT solutions. To obtain a more insightful and quantitative understanding of the impact, the data was used to generate position solutions using our custom navigation processing algorithms in three different ways: pseudorange only, carrier-smoothed pseudorange, and a combination of pseudoranges and carrier-smoothed pseudoranges. The results clearly indicate that sudden carrier phase changes during strong scintillation lead to degradation of carrier-smoothed pseudorange accuracy and consequently, results in large position errors, while the direct use of pseudorange was able to limit the error growth. Based on this analysis, we present an adaptive technique to mitigate scintillation induced position errors. The algorithm simply replaces carrier-smoothed pseudorange with unsmoothed pseudorange for satellites that are affected by cycle slips or experiencing outages on the carrier phase measurements. This results in a navigation solution that maintains consistent accuracy during strong phase scintillations. For comparison purpose, a varied version of this algorithm is also presented, which produces a navigation solution based on unsmoothed pseudoranges for satellites in which a scintillation event is detected. The scintillation detection is achieved by the machine learning algorithm presented in [6]. Carrier-smoothing resumes once the scintillation event subsides. Results show that during segments of data affected by cycle slips, the adaptive positioning technique based on cycle slip detection (AP-CS) is able to reduce position errors by at least 60%, depending on the severity of the phase change. We also discuss alternative approaches for future improvements.
Published in:	Proceedings of the 2017 International Technical Meeting of The Institute of Navigation January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California
Pages:	971 - 988
Cite this article:	Myer, Greg, Morton, Yu (Jade), Schipper, Brian, "Ionospheric Scintillation Effects on GPS Pseudorange and Carrier Phase Measurements and an Adaptive Algorithm to Limit Position Errors during Scintillation," Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 971-988. https://doi.org/10.33012/2017.14945
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