Analysis of RAIM Function Availability of GPS Augmented with Barometric Altimeter Aiding and Clock Coasting

Young C. Lee

Abstract:	The FAA recently formed a group called the Satellite Operational Implementation Team to accelerate the introduction of satellite navigation and communications into the National Airspace System (NAS). The team has staff from various FM organizations such as Flight Standards, Airworthiness, and Aviation Standards, who are responsible for certification and operational approval of avionics and navigation equipment. The team is addressing major technical and operational issues that need to be resolved before GPS is used in IFR flight in the NAS without relying on other navigation systems for integrity. One of the most critical criteria for the operational approval for near-term use of GPS in the NAS is availability of receiver autonomous integrity monitoring (RAIM) detection and identification functions. In or&r to maximize the RAIM availability, relatively simple GPS augmentations in the form of barometric altimeter aiding and clock coasting were suggested. This paper presents the technical analyses used by the team to support its recommendations. This paper analyzes the availability of RAIM detection and identification functions for GPS augmented with barometric altimeter aiding and clock coasting. While some results of this sort are available in the literature, they are not complete enough to provide a basis for FAA decision making. The approach used in this paper is to compute temporal characteristics of ILAIM availability over three major domestic and oceanic routes. The constellations considered include the Optimal 21 and 21+3 Primary constellations, and the 21+3 Primary constellation with a typical set of 3 satellites failed. Tbe results show that significant improvement can be obtained by augmenting GPS with barometric altimeter aiding and a lesser improvement with clock coasting (even with an accurate user receiver clock having a clock drift of lE-9). The barometric akimeter aiding improvement is estimated for two conditions: with GPS calibration and local (at an airport) barometric calibration. The paper shows that the results are highly dependent on the constellation and which satellites are operating.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	951 - 964
Cite this article:	Lee, Young C., "Analysis of RAIM Function Availability of GPS Augmented with Barometric Altimeter Aiding and Clock Coasting," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 951-964.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In