Program

Abstract:

This paper reviews the continuity budget for Advanced Receiver Autonomous Integrity Monitoring Algorithm (ARAIM). It reviews causes of loss of ARAIM service and assess the contributing factors. It then assesses allocations, and in particular, the top-level allocation of continuity for the ARAIM service. Finally, it reviews how the continuity budget might be allocated to a per-sample requirement, following and expanding upon the equation in the ARAIM Algorithm Description Document (ADD) Version 4.1 (RTCA, 2022). Development of ARAIM algorithm requirements includes a preliminary development of the continuity budget. The ARAIM Algorithm Description Document (ADD) Version 3.1 (WG-C, 2019) assesses the impact of actual faults that occur at the core constellation commitment fault rates and concludes that an exclusion algorithm is required for en route and terminal operations. It further then provides an allocation to fault-free detections. The allocation for fault-free detection is applied entirely to the fault detection tests and does not presume an ability to continue operating after a false detection with satellite exclusion. This paper develops an assessment of the probability that an excluded satellite will actually lead to a loss of service. The proposed false alert allocation results in less tolerance for false detections when more satellites are introduced, as there are more fault modes with an associated increase in detection tests. As shown, the introduction of more satellites reduces the dependence on any one satellite, thereby reducing the impact of false detections. While there might be more detection tests and associated detection occurrences if they occur at the same rate, the impact of an unnecessary removal of a satellite due to a false detection also decreases. There is also a difference in the impact of false exclusion of satellites from different constellations. This paper addresses one aspect of the ARAIM continuity budget. Further, this paper develops how these results complement the continuity budget already captured in the ARAIM ADD. This supports the further refinement and understanding of the capability being introduced with ARAIM.