Achieving Theoretical Accuracy Limits for Pseudoranging in the Presence of Multipath

Lawrence Weill

Abstract:	In a recent paper by this author [l], it has been shown that modern GPS receiver- pseudorange estimation techniques, such as narrow correlator technology, ,permit pseudoranging accuracy close to the theoretical iimit for single-path propagation in the presence of receiver thermal noise. As a result, it is now apparent to receiver designers that in a majority of applications, multipath remains as a dominant source of pseudoranging error. Although various receiver processing schemes are being developed to combat multipath error, little has been published about the best performance that is theoretically possible when multipath is actually present. The answer to this question would provide the receiver designer with a valuable benchmark. For example, if the performance of a particular pseuddranging. algorithm in the presence of multipath were close to’ a theoretical limit,. futile and costly attempts to significantly imprcve performance could be avoided. On the other hand, if a significant gap exists between algorithm performance and rneorerrcarry optimum performance, the theory often suggests what mathematical signal processing operations would be required to reach the optimal solution. In this paper, an ultimate limit for pseudorange accuracy in the presence of multipath is developed using results from classical estimation theory. Although the primary focus is on the two-path case encountered in a majority of applications (typified by a direct path and a ground bounce), the theory can be extended to three or more paths. Additionally, the required processing for reaching optimum accuracy is revealed. Subtleties which exist in the case of multipath but not in single-path propagation are also mentioned.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1521 - 1530
Cite this article:	Weill, Lawrence, "Achieving Theoretical Accuracy Limits for Pseudoranging in the Presence of Multipath," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1521-1530.
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