Optimized MHSS ARAIM user algorithms: Assumptions, protection level calculation and availability analysis

This paper describes and further develops two algorithms which are currently being considered by a bilateral EU-U.S. working group on Advanced Receiver Autonomous Integrity Monitoring (ARAIM) called Working Group C (WG-C); the baseline ARAIM MHSS algorithm and an expansion of this approach termed Q*-MHSS. The availability performance, given either an equal or an optimized allocation of integrity and continuity budgets to all failure modes, is assessed. The paper furthermore proposes an improvement to the protection level calculations by introducing a geometry check to exclude weak geometries and corresponding fault modes leading to excessive protection levels. This is relevant in particular when considering constellation-wide consistent faults under relatively high constellation fault probabilities, such as may be necessary when initially starting ARAIM service with constellations that have a limited service history.