Nonlinear Least-Squares Algorithm for Close-in Multipath Mitigation in GNSS Receivers

Fernando D. Nunes, Fernando M.G. Sousa and Jose M.N. Leitao

Abstract:	Multipath is one of the major sources of positioning errors in Global Navigation Satellite System (GNSS) receivers. In general, its effects are completely unpredictable and cannot be mitigated by differential reception techniques. Many different signal processing techniques have been proposed to minimize the multipath problem with different degrees of success depending on the excess delay between the direct path and the secondary path(s) of the incoming satellite signal. In general, they fail to solve the problem for very short excess delays (typically . 0.1Tc, where Tc stands for the code chip duration). However, it is for this range of delays (close-in region) that the distortion suffered by the direct ray may be stronger. It has been demonstrated in [1], [2] that there is room for significant improvement in the performance of the multipath mitigation algorithms operating in the close-in region if alternative approaches to the conventional multipath mitigation techniques are considered. Herein, we propose a technique for close-in multipath minimization based on the Levenberg-Marquardt algorithm. Given a vector of parameters a that contains the delays of the line-ofsight and the reflected ray that hit the GNSS receiver and a set of noisy observations, which depend nonlinearly on a, the Levenberg-Marquardt algorithm determines an iterative best-fit solution to a. Although the algorithm is computationally demanding it is feasible with today쳌fs signal processing technology for the usual update rates of the navigation equation (in the order of one Hz).
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:	1683 - 1691
Cite this article:	Nunes, Fernando D., Sousa, Fernando M.G., Leitao, Jose M.N., "Nonlinear Least-Squares Algorithm for Close-in Multipath Mitigation in GNSS Receivers," 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. 1683-1691.
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