On Correlation Processes Reducing Multipath Errors in the Ll GPS Receiver

Delphine Doris and Abdelahad Benhallam

Abstract:	High-accuracy GPS receivers have been developed and are even able to make sub-meter pseudorange observations. This theoretical accuracy can be improved further through the use of carrier-phase tracking techniques [l-3], but is necessarily degraded by the radio propagation channel. Among the channel disturbances aiTecting both the pseudorange and the carrier phase observables, multipath effects are still a dominant source of error, even when difTerential GPS corrections are available. So for applications requiring high-accuracy, such as precision approach, landing operation or attitude determination, one of the key problem remains the mitigation of the influence of the multipath propagation on the position and velocity estimation processes. The first approach for reducing the induced multipath errors, both on the pseudorange and carrier phase observables, is to isolate the antenna from its surroundings. This generally means the selection of clear antenna sites and appropriate antenna patterns, which is unfortunately not always possible, especially in the case of kinematic applications. So signal processing techniques in the receiver are necessarily required, as it is investigated in the following. The aim of this paper is to present a simulation tool permitting to evaluate the influence of the multipath propagation on both the timing and carrier tracking loops used in conventional GPS receivers. The main encountered receiver architectures, implemented on the COSSAP tool, are described. Specular and diliuse reflection cases are illustrated by simulation results. Classical multipath mitigation techniques are presented and different structures of code tracking loop discriminators - based on a set of correlators using several chip spacings -, are then proposed. It is demonstrated that, by using special structures of correlation, we can greatly reduce the multipath induced errors and compete with structures using space diversity techniques.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	699 - 708
Cite this article:	Doris, Delphine, Benhallam, Abdelahad, "On Correlation Processes Reducing Multipath Errors in the Ll GPS Receiver," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 699-708.
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