KEYNOTE - A Statistical Analysis of GPS L1, L2, and L5 Tracking Performance During Ionospheric Scintillation

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

Abstract:	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. Due to the relatively recent introduction of the new GPS modernization signals L2C and L5, there have been few statistical studies comparing L1, L2C, and L5 tracking performance under real-world scintillation conditions. While the lower frequency carriers generally experience larger signal fluctuations (due to the well-known frequency dependence of scintillation), the different codes and tracking algorithms employed for the different carrier signals make it difficult to predict their vulnerabilities and potential benefits to the NextGen aviation systems that will leverage these signals. Moreover, different GNSS receiver models employ different tracking algorithms which may exhibit unique strengths and vulnerabilities, depending on the characteristics of the scintillating environment. The most direct way to assess the tracking performance for L1, L2C, and L5 during scintillation is by the statistical analysis of experimental data collected using multiple receiver models during the current solar maximum period. With funding and support from the Federal Aviation Administration (FAA), Boston College and National Institute for Space Research (INPE) have been collecting GNSS scintillation observations in Brazil since 2012. Both GPS legacy and triple frequency receivers (L1 C/A, L2C and L5) are represented. As part of our ongoing study to assess GNSS signal tracking performance and navigation accuracy during scintillation, in this paper we report on the probability of losing code lock on L1, L2C, and L5 with two widely used GNSS scintillation monitors, the NovAtel GPStation-6 and Septentrio PolaRxS Pro. The approach we have taken is to count the number of scintillation-induced gaps in the high rate (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 S4 yields the probability of interrupted code tracking as a function of S4. Only high elevation observations are included in the statistics to exclude fluctuations caused by multipath reflections from terrestrial objects. We find that both receivers the NovAtel GPStation-6 and Septentrio PolaRxS Pro generally experienced a higher probability of losing lock on the lower frequency carriers (L2C and L5), 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 ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	1 - 9
Cite this article:	Delay, Susan H., Carrano, Charles S., Groves, Keith M., Doherty, Patricia H., "KEYNOTE - A Statistical Analysis of GPS L1, L2, and L5 Tracking Performance During Ionospheric Scintillation," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 1-9.
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