Alec Katz, Sam Pullen, Sherman Lo, Juan Blanch, Todd Walter, Stanford University; Andrew Katronick, Mark Crews, Robert Jackson, Lockheed Martin

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GNSS is now a cornerstone of civil aviation navigation and supports many applications requiring precise guidance, such as approaches to airports under obstructed visibility. GNSS provides such capabilities through high accuracy and safety assurance of its range measurements and position outputs. GNSS users with demanding safety or integrity requirements but without access to real-time differential corrections and integrity information (e.g., from SBAS or GBAS) can utilize Advanced RAIM, or ARAIM, which is now a well-developed and understood methodology [1][2]. ARAIM extends and improves upon traditional RAIM algorithms to detect and mitigate independent and correlated GNSS signal faults, making it possible to support applications such as aviation precision approach without requiring continuous integrity messages supporting a 2-to-6 second time-to-alert. Civil ARAIM uses multiple GNSS constellations to provide availability approaching what is obtainable from augmented GPS while detecting or otherwise mitigating faults correlated across a single constellation. However, ARAIM for U.S. military users may be limited to use of the GPS constellation only [3][4]. This paper describes and evaluates the performance of ARAIM using only GPS M-code for positioning as a function of its Integrity Support Message (ISM) parameters and the frequency with which these parameters are updated. In order to detect potential GPS constellation-wide faults, it also develops a new variant of ARAIM in which open-service signals from another constellation (Galileo) are used in a position-domain constellation check without being used for positioning.