Multipath Mitigation using Modernized GPS Signals: How Good Can it Get?

Lawrence R. Weill

Abstract:	Proposed changes in the civil and military GPS signal structures offer the possibility of improved in- receiver multipath mitigation in high-performance differential positioning systems. In such systems, multipath remains a dominant error source despite a great deal of effort by researchers and receiver manufacturers to reduce it. Mitigation of multipath errors is especially difficult when the relative delay between the direct and secondary propagation paths is small (approximately 5-20 meters). In this case, estimation of the direct path delay is an ill- conditioned parameter estimation problem. Some work has already been done to characterize the multipath performance of modernized GPS signals using standard receiver pseudoranging techniques not specifically designed for multipath mitigation, for example, in [3]. It is expected that techniques which have been popular for multipath mitigation of C/A-coded signals will be evaluated for their effectiveness with the new signals. However, an important question remains: Can we determine the best that can be done with any form of processing? The answer is not just of theoretical importance. It not only provides the GPS receiver designer with a valuable benchmark for algorithm design efforts, but the theory often suggests the mathematical signal processing operations required to reach upper performance limits. This paper presents pseudoranging and carrier phase estimation performance of a new high- performance estimator, called Multipath Mitigation Technology (MMT), which is a computationally economical method of reaching a theoretical performance limit previously developed by the author in [6] for a multipath environment. The pseudoranging performance of MMT in this environment is compared with that of the optimal estimator designed for a non-multipath environment, and also is compared with the performance of a popular multipath mitigation technique recently developed by GPS receiver manufacturers. Results are presented for each type of GPS signal available after current modernization efforts are completed. For simplicity of exposition, a two-path signal model is used throughout this paper, although an extension to a larger number of paths is not difficult.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	493 - 505
Cite this article:	Weill, Lawrence R., "Multipath Mitigation using Modernized GPS Signals: How Good Can it Get?," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 493-505.
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