GPS multipath model validation

Multipath represents the dominant error source in satellite-based precision guidance systems. Since multipath errors are not common to the reference station and remote receivers, they are not eliminated through differential corrections and they do not cancel out in a differential carrier-phase tracking system. For precision approach applications, multipath is the most significant obstacle to overcome in the quest for CAT III accuracy and integrity using code-DGPS. Although a multitude of GPS articles discuss the effects of multipath, few derive the basic relationships between the composite signal at the antenna and the resulting measurement error. Furthermore, no validation of the aforementioned theory has been performed to date. This paper presents a comprehensive treatment of the problem. The traditional theoretical multipath error relationships are presented along with validation results obtained from bench-testing using a multichannel satellite simulator. Results are presented for standard and narrow-correlator C/A-code architectures as well as standard P-code. One result of particular interest to the aviation community is validation of the theoretical results which indicate that airframe-based multipath error cannot be reduced with narrow-correlator or P-code technology