Code and Phase Multipath Characterization for Beam-Steering Receivers

Ryan J. Eggert, Jose R. Gutierrez, and John F. Raquet

Abstract:	The random nature of GPS signal multipath creates signal tracking errors that are very difficult to overcome. Fortunately, these errors can be dismissed for general GPS applications. Other applications, however, do require a solid understanding of the multipath environment in order to meet their objectives. One such case is the Joint Precision Approach and Landing System (JPALS) which has very high integrity requirements. For the JPALS program, a thorough understanding of all error sources is desired, particularly in worst-case error scenarios. This paper characterizes the GPS signal multipath from two different beam-steering receivers at four different locations around Wright-Patterson Air Force Base, Ohio (WPAFB). Each location was chosen for analysis of the effects in different environments: a field with no structures nearby provided a baseline for comparison, a softball field with many chain-link fences around the antenna, an intersection with many vehicles driving by, and a rooftop with multiple structures and pieces of equipment nearby. The receivers used a 7-element antenna in both beam-steering and conventional modes. One goal of this research is to demonstrate techniques that characterize the effects of beam-steering on both code and phase multipath. The signal multipath is isolated using two different techniques: 1) a multiple receiver condition adjustment method and 2) dual-frequency divergence-free code-carrier smoothing. Method (1) uses data from three additional nearby stationary receivers to estimate the multipath. An advantage of this method is that it can be used to determine both code and phase multipath independently. Method (2) uses a code-carrier smoothing technique to estimate code multipath. Results are presented in a variety of ways, including standard statistical analysis, analysis of the probability density function, and frequency analysis of the signal. Particular emphasis is given to the worst-case multipath values.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	551 - 560
Cite this article:	Eggert, Ryan J., Gutierrez, Jose R., Raquet, John F., "Code and Phase Multipath Characterization for Beam-Steering Receivers," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 551-560.
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