Fault Detection and Elimination for Galileo-GPS Vertical Guidance

Alexandru Ene, Juan Blanch, and J. David Powell

Abstract:	In anticipation of the future launches of dual-frequency GNSS satellites, such as Galileo and GPS block III, a series of new developments has taken place in the field of Receiver Autonomous Integrity Monitoring (RAIM). Of particular interest were the topics of multi-constellation RAIM and analyzing the impact of multiple simultaneous ranging failures. Given the expected increase in the number of ranging sources for the aviation user, a breakthrough is expected to be made in the use of satellite navigation for precision approaches and other critical operations. The reduction in nominal error bounds by removal of the ionospheric delay term from the measurements, together with the presence of a larger number of satellites is going to increase the robustness against satellite failures and hazardous pseudorange errors. Vertical errors are critical during aviation precision approaches, and they are also generally greater than horizontal errors for satellite-based positioning. The purpose of this work is to investigate what Vertical Protection Level (VPL) values could be achieved with an unaided combined Galileo-GPS constellation under conservative failure assumptions. The foundations that enable the methods developed in this paper have already been laid in previous work [2] by identifying a viable RAIM algorithm for monitoring dual-frequency ranging signals and conducting detailed parametric studies to identify what threat space needs to be covered with future RAIM algorithms. Given a better understanding of the threat model and the proposed multiple hypothesis algorithm, the final contribution to a new dualconstellation RAIM is made here as a detailed study of a Failure Detection and Elimination (FDE) method, with the purpose of improving the navigation Protection Level (PL) where possible. Virtual simulations of this new technique have been conducted and preliminary results indicate that VPLs in the vicinity of 10m under nominal conditions are achievable. These protection levels will likely enable LPV 200 landings at all runway ends in the world without the need for a Ground or Space-Based Augmentation System (GBAS or SBAS). Furthermore, since the PL is a direct function of the measurement residuals under this approach, a tool will be developed for predicting VPL values ahead of time, before a critical navigation operation is set to begin. A conclusion will be presented on the capabilities of dualconstellation RAIM to assist an aviation user in meeting the integrity and continuity requirements for landing aircraft. The future capabilities and limitations of RAIM usage for aviation precision approaches with GNSS as the primary means for navigation will also be discussed in the context of current aviation navigation requirements for landing and take-off. Also, the need for ground aiding to the aviation user equipped with RAIM will be assessed.
Published in:	Proceedings of the 2007 National Technical Meeting of The Institute of Navigation January 22 - 24, 2007 The Catamaran Resort Hotel San Diego, CA
Pages:	1244 - 1254
Cite this article:	Ene, Alexandru, Blanch, Juan, Powell, J. David, "Fault Detection and Elimination for Galileo-GPS Vertical Guidance," Proceedings of the 2007 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2007, pp. 1244-1254.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In