Bounding continuity risk in H-ARAIM FDE

Future dual-frequency, multi-constellation advanced receiver autonomous integrity monitoring (ARAIM) is expected to bring significant navigation performance improvement to civil aviation. Among the two ARAIM schemes that are being investigated, horizontal ARAIM (H-ARAIM) aims at providing horizontal navigation for aircraft en-route, terminal, initial approach, non-precision approach (NPA) and departure operations. Because most of those operations cannot be easily aborted once started, H-ARAIM continuity requirements are stringent, and loss of continuity (LOC) for H-ARAIM is considered a serious safety event. In this paper, we address the impact of detected faults and unscheduled satellite outages (USO) on H-ARAIM continuity, develop new methods to quantify continuity risk, and investigate H-ARAIM overall availability performance accounting for both integrity and continuity. Using multi-constellation global navigation satellite systems (GNSS), the heightened likelihood of the user encountering a fault or USO could significantly increase continuity risk. In response, our previous work explored implementing an exclusion function to improve continuity after fault detection, and, separately, analyzed critical satellites to assess the impact of USO on H-ARAIM continuity. In this work, we derive a more rigorous continuity risk equation that quantitatively accounts for the LOC contributions from both measurement faults and USO. This new approach unifies the separate critical satellite analysis into one integrity risk equation, which characterizes the integrity threat under USO conditions. Moreover, this approach allows us to determine whether an exclusion function is still needed following a USO event. With this new method fully described and derived, the last part of the paper applies it to analyze H-ARAIM availability performance. The results indicate that dual-constellation H-ARAIM can provide high service availability, where both integrity and continuity requirements are met.