Reduced ARAIM Subsets Method Determined by Threshold for Integrity Risk

Advanced Receiver Autonomous Integrity Monitoring (ARAIM), based on multi-constellation and multi-frequency of global navigation satellites system, which can provide vertical navigation in terminal approach, has attracted more attentions. The ARAIM user algorithm is based on the multiple hypothesis solution separation within the Integrity Support Message. The total probability of the monitored fault modes subsets must meet the integrity budget. In ARAIM baseline algorithm, the fault mode determination is an independently sequential structure. The number of subsets determined by the maximum simultaneous faults number is redundant which increases computational burdens in fault-tolerant position. A refined subsets determination method is proposed to optimize the calculation. Instead of determining the maximum simultaneous faults number, the proposed method accumulates the fault mode in descending order according to the probability. The threshold for the integrity risk coming from the unmonitored faults is the only parameter to terminate this accumulation and determine the number of subsets. Every subset will be detected the observability and continuity further in this process to make sure that ARAIM can work normally. The structure is more compact and reasonable. The tests results shown that the proposed method is more rigorous as the accumulation processing can make sure the monitored subsets meet the threshold exactly and the accuracy of not monitored risk is increased by three orders of magnitude. The global 99.5% coverage under LPV-200 requirements can be up to 95.94%. The number of subsets is reduced more than 80% significantly without any impacts to the worldwide performance of ARAIM.