Parametric and Statistical Characterization of Multipath Errors for Galileo Signals

J.M. Lopez-Almansa, J. Cosmen-Schortmann, P. Coutinho, and M. Toledo

Abstract:	Multipath remains as one of the main sources of error for satellite navigation. Characterization of multipath is essential in order to assess the performance of the navigation system, in several aspects: pseudorange accuracy, integrity, ambiguity resolution, etc. In the literature, multipath performance is often characterized by the so-called multipath envelopes, where the maximum multipath error is shown against the delay of one single reflection, for a given relative power. Other more sophisticated characterization models are also published, where multipath is analyzed in probabilistic terms, by making assumptions about the external multipath channel, and managing it through random variables with specific probability distributions (Montecarlo analysis). This paper is more in line with the later approach: random-variables will be used to model the delay of the reflections, and the characterization metric will be based on percentile curves of the multipath error experienced by the receiver. However, a certain level of parameterization is kept to organize the results, with the percentiles being presented as families of curves for two parameters: number of simultaneous reflections and total reflected power. It is believed that this approach provides a means to analyze the multipath from a novel perspective: • On the one hand, it will be shown that the number of simultaneous reflections play a relevant role on characterization of the multipath error, since, even keeping the total multipath power constant, the number of rays (contributing towards that constant power) impacts significantly the expected multipath error for some Galileo signals, receiver conditions and confidence levels. • Moreover, the percentile curves can help to understand how close the multipath error is to the Gaussian behavior (which can be important to justify or not the Gaussian extrapolations typically used for computation of integrity levels, and other matters, like probabilities of ambiguity resolution). The analysis will be detailed for three Galileo modulations, by using conventional narrow correlator as well as for two specific and well-known multipath mitigation techniques (APME & HRC). However, the methodology presented here would be fully applicable to any other GNSS signal.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1722 - 1732
Cite this article:	Lopez-Almansa, J.M., Cosmen-Schortmann, J., Coutinho, P., Toledo, M., "Parametric and Statistical Characterization of Multipath Errors for Galileo Signals," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1722-1732.
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