User Differential Range Error Algorithms for the Wide Area Augmentation System

Stephen Peck and Jonathan Tekawy

Abstract:	Hughes is currently designing and implementing the Wide Area Augmentation System (WAAS) for the Federal Aviation Administration (FAA). The system consists of space, ground and user segments. The ground segment of WAAS includes reference stations, master stations, GE0 uplink stations and terrestrial communication system. One critical component of the WAAS ground data processing is the various correction and validation algorithms designed to meet the accuracy, integrity and safety requirements for the users. This paper presents one of these correction and validation algorithms called “User Differential Range Error (UDRE) algorithm”. The paper also summarizes the performance evaluation and validation results for the initial WAAS architecture. The UDRE algorithm objective is to meet the WAAS integrity function specification. This specification requires that the WAAS system provides the users with the User Differential Range Error Indicator (UDREI) tbr each satellite in view from the WAAS network. This indicator essentially informs the user of the accuracy level of the combined fast and slow error corrections within the time-to-alarm requirement. In order to determine the UDREI, the UDRE algorithm computes the UDRE bound using the statistical properties and 99.9% tolerance interval values of the recent WAAS reference station measurements as well as the WAAS signal in space data. The algorithm then specifies a value for the UDREI based on the WAAS message structure. Performance analyses using a simulation based on real data results have been documented for the UDRE algorithm. The simulated data analysis provides a preliminary check and a way to test the algorithm fbr cases with anomalous conditions. The performance analysis results show that the algorithm evaluated produces UDRE bounds that confine the ephemeris and satellite clock errors without excessive margins. The results also show that the algorithm captures and bounds the error residuals promptly within the time to alarm specification even for cases with anomalous conditions. These results suggest that the algorithm implemented provides the users with an integrity check of the WAAS’s corrections with 99.9% confidence.
Published in:	Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997) June 30 - 2, 1997 Albuquerque, NM
Pages:	421 - 429
Cite this article:	Peck, Stephen, Tekawy, Jonathan, "User Differential Range Error Algorithms for the Wide Area Augmentation System," Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997), Albuquerque, NM, June 1997, pp. 421-429.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In