Improving Path Separation in a Multipath Environment by Applying Nonlinear Estimation Theory

Karl Kaindl and Norbert Niklasch

Abstract:	Multipath problems are often caused by multiple reflections from buildings or nearby objects in an urban environment, so called urban canyons. This fact can cause DLL-pseudorange-errors up to 30 m [Braasch]. It also indicates that in many applications, multipath effects remain a major error source. Some publications ([Weill], [Townsend]) discuss the limits for pseudoranging in the presence of multipath effects which depend much on the quality of path separation [Weill]. Even by applying elaborated methods ([Weill], [Xia] ,[Soubielle]), multipath is still a complex problem which is not sufficiently solved algorithmically. Therefore we have pointed out in [Kaindl] how nonlinear estimation theory is connected to the problem of solving nonlinear higher dimensional equations numerically (usually 4-dimensional in case of a 2-path way). The algorithmic solution of nonlinear higher dimensional equations has shown that a reliable and stable situation of the two main problems (initial start, convergence problems) can be achieved algorithmically. For application we generated three typical multipath situations and created the DLL-tracking error for a non coherent discriminator in each case. To minimise the computational load we combined geometrical and numerical attitudes of the sampled multipath correlator outputs. This reduced the root finding costs by a factor two for we isolated the time delayed parameters before launching root finding procedures. We created a set of multipath simulations with a 2MHz Butterworth filter and a second one with a 8MHz Butterworth filter as correlator output. Simulation results show in each case that even in critical multipath situations (delay = 100ns, amplitude = 0.5) a significant improvement of the pseudorange error was achieved.
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:	472 - 476
Cite this article:	Kaindl, Karl, Niklasch, Norbert, "Improving Path Separation in a Multipath Environment by Applying Nonlinear Estimation Theory," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 472-476.
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