A Statistical Comparison of Satellite Tracking Performances During Ionospheric Scintillation for the GNSS Constellations GPS, Galileo and GLONASS

Susan H. Delay, Charles S. Carrano, Keith M. Groves, Patricia H. Doherty

Abstract:	Global navigation satellite systems (GNSS) consist of a constellation of satellites providing continuous navigation signals at two or more frequencies in the L band. The signals contain ranging code and navigation data. GNSS navigation accuracy in the presence of ionospheric scintillation depends critically on tracking loop performance, which can be characterized in terms of the probability of loss-oflock (LOL) and the time for signal reacquisition following LOL events. One way to increase the margin of performance of the GNSS service is to increase the number of satellites tracked. The more satellites available for tracking, the more likely some links will be unaffected by scintillation during disturbed ionospheric conditions. Further, a larger contingent of satellites implies that a user can tolerate more noise on their measurements. Therefore, incorporating as many satellites as possible may be an effective means of mitigation. To this end, the worldwide community has joined the United States in launching satellite navigation systems of their own. Here we consider three GNSS systems, GPS, Galileo (European) and GLONASS (Russian). Other systems, BeiDou/Compass(China) and IRNSS (India) continue to expand but we did not monitor their signals. At this juncture, there have been few studies comparing the tracking performances of various GNSS systems under real-world scintillation conditions. This paper will compare the effects of scintillation on both L1 and L2C frequencies found on GPS, GLONASS and Galileo satellites and recorded by a GNSS Septentrio PolaRxS Pro scintillation monitor operating as part of the CIGALA network in Brazil. The data we examined was for March 2015. Our methodology is to count the number of scintillation-induced gaps in the high rate A Statistical Comparison of Satellite Tracking Performances During Ionospheric Scintillation for the GNSS Constellations GPS, Galileo and GLONASS Susan H. Delay, Charles S. Carrano, Keith M. Groves, Patricia H. Doherty Institute for Scientific Research, Boston College, Chestnut Hill, MA (50 Hz) receiver-reported signal amplitudes. Next, we bin these data gaps as a function of the scintillation index, S4. The ratio of the number of missing samples to the total number of samples for a given value of S4 yields the probability of interrupted code tracking as a function of S4. We examined the effect of four different elevation masks on the statistics of scintillation-induced outages: 10º, 20º, 30º and 40º. We found similar results across the constellations even though the amount of data per constellation varied greatly. We attribute this parity to our method of normalizing the data associated with each constellation. We observed a strong correlation between the masking elevation and the probability of losing lock. The lower the mask value, the higher the contribution from multipath leading to an increased probability of loss-of-lock due to scintillation. Very few loss-of-lock events were observed at high elevation angles, suggesting that the effects of scintillation and multipath together were responsible for most of the loss-of-lock events observed. Also, there appears to be a higher probability of losing lock on the lower frequency carrier, L2C, even when quantified in terms of S4 on the same carrier, despite the enhanced codes and advanced tracking techniques available for these modernization signals.
Published in:	Proceedings of the 2016 International Technical Meeting of The Institute of Navigation January 25 - 28, 2016 Hyatt Regency Monterey Monterey, California
Pages:	540 - 548
Cite this article:	Delay, Susan H., Carrano, Charles S., Groves, Keith M., Doherty, Patricia H., "A Statistical Comparison of Satellite Tracking Performances During Ionospheric Scintillation for the GNSS Constellations GPS, Galileo and GLONASS," Proceedings of the 2016 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2016, pp. 540-548. https://doi.org/10.33012/2016.13397
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