Validation of GPS Fading Multipath Effects through Modeling and Simulation

Joseph M. Kelly and Michael S. Braasch

Abstract:	The development of higher precision navigation and guidance techniques using GPS requires that certain sources of error, previously thought trivial, be dealt with under greater scrutiny. Theoretical studies have shown bias errors caused by multipath signals having a large relative Doppler shift with respect to the receiver code-tracking loop bandwidth. These so-called fast-fading multipath signals have effects that are dependent on the chosen receiver tracking loop architecture. Two loops are considered. The performance of the non-coherent delay lock loop (NCDLL), widely used for its robustness, is compared with the less popular coherent delay lock loop (CDLL). In theory, the NCDLL will estimate the multipath corrupted code phase with a certain non-zero bias, dependent on multipath parameters. For the CDLL, the bias theoretically is reduced to zero. This paper will summarize the aforementioned theory and will describe a hardware simulator setup used to evaluate receivers of each loop type. The CDLL will be implemented in software that will replace the NCDLL software in an identical off-the-shelf hardware receiver. This substitution will allow isolation of multipath effects on the code phase estimation by canceling hardware specific errors. The results of these simulator tests will be compared with theoretical predictions and modeled data.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	684 - 690
Cite this article:	Kelly, Joseph M., Braasch, Michael S., "Validation of GPS Fading Multipath Effects through Modeling and Simulation," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 684-690.
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