NIORAIM Integrity Monitoring Performance In Simultaneous Two-Fault Satellite Scenarios

Patrick Y. Hwang and R. Grover Brown

Abstract:	The RAIM (Receiver Autonomous Integrity Monitoring) concept has been well known to the navigation community for more than a decade now, together with its shortcomings in availability. More recently, a new method called NIORAIM for achieving a better balancing of position accuracy with integrity was introduced using non-uniform weighting of the measurements. The method involves the selection of an optimum set of weights to get the lowest protection limit and efficient ways of evaluating the protection limit in light of the sub-optimality of the solution. The results from the analysis of NIORAIM performance showed that, for the NPA phase of flight where baro-aiding is available, about 50% of the unavailable geometries derived using standard RAIM-FDE could be salvaged when using NIORAIM. In this paper, the NIORAIM method will be extended to solve the problem of handling two simultaneous faults. Modifications to the NIORAIM algorithm are necessary to compute the horizontal integrity limit and evaluate the best set of weights under the new assumption of the worst case effect of encountering two satellite faults occurring simultaneously. NIORAIM was already a more complex algorithm than the original RAIM, particularly in the area of computing the integrity limits. With the two-fault assumption and its increased number of hypotheses resulting from the different paired satellite fault combinations, the ratio of the fault sizes between the two satellites of each pair must also be accounted for. The worst case ratio can be solved with Lagrangian multipliers when dealing with "slopes" in the noiseless analysis but the computational issues are less straightforward when accounting for noise. A design based on lookup tables with precomputed data will be presented in the paper that is amenable to real-time computation. The paper also discusses notions of designing a system to unify the handling of single and dual fault situations.
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:	1760 - 1771
Cite this article:	Hwang, Patrick Y., Brown, R. Grover, "NIORAIM Integrity Monitoring Performance In Simultaneous Two-Fault Satellite Scenarios," 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. 1760-1771.
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