High-Performance Multipath Mitigation Using the Synergy of Composite GPS Signals

L.R. Weill

Abstract:	Starting with the narrow correlator in 1992, the development of GPS signal processing techniques to reduce pseudorange and phase measurement errors due to multipath have met with varying degrees of success. Some of these methods are effective in mitigating error caused by far multipath, when secondary propagation paths are delayed by more than 20-30 meters relative to the direct path. Unfortunately, however, none of the signal processing techniques currently used in GPS receivers solves the problem of close-in multipath, in which relatively short secondary path delays are experienced. Close-in multipath is particularly troublesome for two reasons related to the nature of the secondary path signals. These signals can be very strong due to reflection from the ground or other objects close to the receiver antenna. Additionally, their small relative delays make it difficult to distinguish them form the desired direct path signal. In general, the result is an ill-conditioned parameter estimation problem. The newly-developed civil and military modernized GPS signal structures offer the possibility of improved receiver-based multipath mitigation in high-performance differential positioning systems. Last year this author presented in [1] an ultimate performance limit for each modernized signal and a practical algorithm for achieving it. Worst-case residual errors with close-in multipath were shown to be almost an order of magnitude below that obtained with current popular mitigation methods. The ultimate performance limits for receiver-based multipath mitigation in [1] are based on the assumption that only one type of GPS signal is used to make the pseudorange and/or carrier phase estimates. It is clear that simultaneous use of more than one signal type should drive these limits toward a smaller error. This paper demonstrates a high-performance multlipath mitigation algorithm based on simultaneous reception of the L2 civil and L5 civil GPS signals, using maximum likelihood estimation of both code- and carrier-based pseudorange. The performance of the algorithm is substantially better than that obtained in [1] from either L2 or L5 alone.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	829 - 840
Cite this article:	Weill, L.R., "High-Performance Multipath Mitigation Using the Synergy of Composite GPS Signals," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 829-840.
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