Development of an Error Budget for a GPS Wide-Area Augmentation System (WAAS)

M. Bakry El-Arini, Christopher J. Hegarty, James P. Fernow, John A. Klobuchar

Abstract:	The Federal Aviation Administration (FAA) Satellite Program Office, ARD-70, is developing a GPS Wide-Area Augmentation System (WAAS) to meet precision approach horizontal and vertical position accuracy requirements down to or near the lowest Category I (CAT I) decision height of 200 ft. In the candidate architecture under development, a vector of corrections is sent to user avionics via geostationary communication satellites (e.g., Inmarsat). This correction vector includes components for ionospheric, clock, and ephemeris corrections. The purpose of this paper is to develop an error budget for such a system based on the Required Navigation Performance (RNP) Total System Error or “Tunnel” Concept. The main components of this error budget are ionospheric, clock, and ephemeris errors in the WAAS- corrected signal-in-space, and tropospheric, receiver noise and multipath errors due to avionics. The ionospheric error is based on the WAAS ionospheric grid algorithm previously developed by MITREKAASD and the Air Force Phillips Laboratory (AFPL). The clock and ephemeris errors are based on the current performance of Selective Availability (SA), the proposed RTCA SC 159 WG2 message format, measurement errors at WAAS ground stations, and the inherent accuracy of orbital estimation algorithms. The tropospheric error is based on the model developed by the Air Force Cambridge Research Laboratory (AFCRL). The receiver noise and multipath errors are based on data obtained from the literature on narrow-correlator spacing receivers.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	927 - 936
Cite this article:	El-Arini, M. Bakry, Hegarty, Christopher J., Fernow, James P., Klobuchar, John A., "Development of an Error Budget for a GPS Wide-Area Augmentation System (WAAS)," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 927-936.
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