Performance Evaluation of Combined L1/L5 Kalman Filter-Based Tracking versus Standalone L1/L5 Tracking in Challenging Environments

D. Megahed, C. O'Driscoll, G. Lachapelle

Abstract:	The ever-increasing demand on GPS to perform in challenging environments is the main motivation behind this research. Different challenging environments include –but are not limited to– suburban environments suffering moderate multipath, urban canyons suffering strong multipath and fading, indoor environments suffering multipath and weak signals. With the existence of these different scenarios that require higher sensitivity of the GPS, more research is directed towards enhancing both the acquisition and tracking capabilities. Considering signal tracking, which is the focus of this paper, several solutions have been proposed to enable high sensitivity tracking. Using one signal, increasing the integration time is one means for enhancing the tracking sensitivity, though it always faces the need to estimate the data bits correctly. New GPS signals, e.g. L2C, L5 are now available, in addition to the conventional L1 C/A code signal. Being transmitted from the same space vehicle through the same environment, the errors between these signals are correlated. Hence, an increase in tracking sensitivity can be achieved by combining two or more of these signals. Megahed et al (2009) have investigated the idea of combining the L1 C/A code and the L5 signals using one Kalman filter, where the correlator outputs of the two signals are used to estimate the tracking errors. However, it compared the combined Kalman filter to the traditional tracking loops. That comparison provides an estimate of the performance of the suggested tracking filter. Yet it is lacking a completely fair comparison due to the difference in nature between the Kalman filter and the traditional tracking loops in general. To provide an entirely fair comparison, this paper continues the analysis of the combined Kalman filter, but comparing its performance to a similar Kalman filter that is used separately for tracking each of the two signals. The performance of both the separate and the combined Kalman filters are compared in environments suffering urban canyon multipath, moderate ionospheric errors, in addition to a motion model of a typical vehicle. The comparison criteria include the tracking loop lock indicators –the phase and frequency lock indicators– of both the L1 and the L5 signals. In addition, the Kalman filters state estimates and standard deviations are analyzed to confirm the quality of the tracking.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2591 - 2601
Cite this article:	Megahed, D., O'Driscoll, C., Lachapelle, G., "Performance Evaluation of Combined L1/L5 Kalman Filter-Based Tracking versus Standalone L1/L5 Tracking in Challenging Environments," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2591-2601.
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