Validation of the Airframe Multipath Error Allocation for Local Area Differential GPS

Janet Booth, Tim Murphy, Barbara Clark and Fan Liu

Abstract:	The International Civil Aviation Organization (ICAO) Global Navigation Satellite System (GNSS) Panel (GNSSP) has developed Standards and Recommended Practices (SARPs) for Ground Based Augmentation Systems (GBAS) and Space Based Augmentation Systems (SBAS). The RTCA Special Committee 159, Working Group 4A (WG-4A) has also developed the Minimum Operational Performance Standards (MOPS) for airborne GPS/Local Area Augmentation System (LAAS) and GPS/Wide Area Augmentation System (WAAS) receivers. These standards include an airborne error allocation for airframe multipath defined by a common error model. This model is intended to apply to all GBAS (i.e. LAAS) or SBAS (i.e. WAAS) receivers installed on any aircraft within a reasonable set of installation guidelines. The motivation for standardizing the error model is to fix the allocation for receiver tracking performance and limit test requirements to evaluating that tracking performance. Testing of airframe multipath on each aircraft model would be very impractical and expensive. This paper describes the validation activity that has been done to show that the standard error model for airframe multipath is adequate. The standard multipath error model is presented and discussed in the context of the allocation of SARPs and MOPS requirements. The expected magnitude of airborne multipath based on theoretic considerations is discussed. The paper then presents the methods used to estimate the multipath error as well as the difficulties experienced in isolating the multipath error component from in-flight measurements. The in-flight measurements were recorded during long duration flights of a number of aircraft including the Boeing 727, 737, 747, 757, 767 and 777 airplanes. The paper concludes with the results and interpretation of the validation activities. This activity is significant because it represents the most comprehensive study of airframe multipath on commercial air transport airplanes to date. The study shows that for commercial applications, an allocation for airborne multipath that is independent of the specific aircraft type is feasible.
Published in:	Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000) June 26 - 28, 2000 The Catamaran Resort Hotel San Diego, CA
Pages:	689 - 698
Cite this article:	Booth, Janet, Murphy, Tim, Clark, Barbara, Liu, Fan, "Validation of the Airframe Multipath Error Allocation for Local Area Differential GPS," Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000), San Diego, CA, June 2000, pp. 689-698.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In