Alternative Characterization of Analog Signal Deformation for GNSS-GPS Satellites

G. Wong, R.E. Phelts, T. Walter, P. Enge

Abstract:	Currently, analog signal deformation is described using individual-chip step response curves for each GPS/WAAS-GEO satellite. Such a set of curves is helpful – it allows us to have an overall idea of the distortions for all satellites as well as identify possibly anomalous satellite signals. However, the step response curves do not convey the severity of the distortions to the user in a metric he/ she can intuitively grasp. In addition, there is no current specification for nominal analog deformation. The ICAO model describes only the faulted mode. In this paper, we propose an alternative method of characterizing nominal analog distortion: using the change in behavior of early-minus-late (EML) tracking errors across different correlator spacings. Such a measurement metric is more user-intuitive, and is directly related to user-domain parameters of interest such as pseudorange and position errors. In turn, these errors are of great importance to the performance and integrity of satellite-based augmentation systems (SBAS) and ground-based augmentation systems (GBAS). Two different methods to obtain such tracking error curves are described and compared – processing of satellite dish antenna raw data and hardware GPS receiver outputs. Error sources affect the accuracy of our tracking error plots; for the satellite dish method these error sources and mitigation procedures are illustrative and discussed. The results from the two methods are presented and compared. The predicted inter-satellite tracking error plots are also compared to those observed from actual hardware receivers. For additional verification, results from the tracking error plots for particular correlator spacings are also compared to errors from actual hardware receiver pseudoranges with the same correlator spacings. Future work for both these methods is also proposed.
Published in:	Proceedings of the 2011 International Technical Meeting of The Institute of Navigation January 24 - 26, 2011 Catamaran Resort Hotel San Diego, CA
Pages:	497 - 507
Cite this article:	Wong, G., Phelts, R.E., Walter, T., Enge, P., "Alternative Characterization of Analog Signal Deformation for GNSS-GPS Satellites," Proceedings of the 2011 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2011, pp. 497-507.
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