GPS and Galileo with RAIM or WAAS for Vertically Guided Approaches

Young C. Lee, Ronald Braff, J. P. Fernow, Deihim Hashemi, Michael P. McLaughlin and Daniel O'Laughlin

Abstract:	The study described in this paper is an investigation of the extent to which the improved position determination capability of a combined GPS/Galileo could be used to provide or increase availability of navigation guidance for vertically guided approaches by 1) enabling the use of receiver autonomous integrity monitor (RAIM); and 2) extending the capability of the Wide Area Augmentation System (WAAS). The scope of the study includes the formulation of target operational requirements, the modeling of navigation system performance with respect to the requirements, and the evaluation and interpretation of the study results, which are derived from a service volume model (SVM). The SVM outputs availability as a function of integrity alert limits, subject to constraint parameters concerned with integrity risk, continuity risk, accuracy, and satellite elevation mask angle. The analyzed geographic areas are the 48 states and Alaska. The RAIM model is based on a new method, which was developed for application to combined GPS/Galileo, and is described here in detail. The assumed WAAS model is an evolution of the present WAAS that is upgraded with more reference stations and dual-frequency capability. Among the results indicated by the study are the following: • Combined GPS/Galileo with dual-frequency, assuming the achievement of user range accuracy (URA) = 0.5 m, has the potential for RAIM to achieve a vertical alert limit (VAL) = 20 m (availability = 0.99). RAIM operating with only a single constellation would not be suitable for vertical guidance during instrument approaches. • Future WAAS operating with combined GPS/Galileo with dual frequency and user differential range error (UDRE floor) = 1 m has the potential to support a VAL = 10 m (availability = 0.9995). Future WAAS operating with GPS only with dual frequency and UDRE floor = 1 m has the potential to support a VAL = 20 m (availability = 0.995).
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1801 - 1825
Cite this article:	Lee, Young C., Braff, Ronald, Fernow, J. P., Hashemi, Deihim, McLaughlin, Michael P., O'Laughlin, Daniel, "GPS and Galileo with RAIM or WAAS for Vertically Guided Approaches," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1801-1825.
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