Optimal Positioning for Advanced RAIM

J. Blanch, T. Walter, P. Enge

Abstract:	In the next decade, several important developments will have a major impact on civil aviation: the deployment of Galileo and Compass, the modernization of GPS, and the fact that all these core constellations will broadcast navigation signals in two distinct signals that fall in the L1/E1 and L5/E5, which fall in both the Radio Navigation Satellite Service (RNSS) and the Aeronautical Radio Navigation Satellite Service (ARNSS). As a consequence, even under conservative assumptions, there will be over three times more ranging sources than today. In addition, the ionospheric delay will be estimated and removed by the receiver using dual frequency. These developments can be exploited in all satellite navigation systems for aircraft. In particular, the increased redundancy and accuracy could dramatically improve the performance of Receiver Autonomous Integrity Monitoring (RAIM). In Advanced RAIM (ARAIM), they could help enable worldwide for vertical guidance. For horizontal RAIM, it could help achieve worldwide coverage of lateral navigation down to fractions of a mile. It is therefore useful to evaluate which RAIM algorithms offer the best performance. As shown in [1], [2] the performance of RAIM can be improved by optimally allocating the integrity budget and the continuity budget across the fault modes – in order to minimize the Protection Levels. The approach in [1] and [2] assumes that the position is centered at the most accurate all-in-view position. This approach guarantees the best accuracy under nominal conditions. However, it is possible to reduce the Protection Levels by choosing a position solution that minimizes it – therefore degrading accuracy. This approach has been exploited in NIORAIM within the framework of slope-based RAIM, where single faults are assumed [3] and accuracy constraints are not considered. It has also been exploited in the case of a simplified threat model where only constellation faults are assumed in [4]. The contribution of this paper consists on simultaneously optimizing the integrity allocation and the position solution, in taking into account additional constraints when generating the position solution - for example the accuracy, but not only -, and in doing it for any threat model (in particular multiple faults). This is done by casting the problem as a convex optimization problem. We will evaluate this algorithm by comparing its performance with algorithms where the position solution is not optimized, and showing how it could help achieve worldwide coverage of vertical guidance (LPV-200) under different sets of assumptions.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1624 - 1647
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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