SIS Monitoring for ARAIM in the Absence of Precise Clock Estimates

This paper describes methods for constellation monitoring in the absence of external precise clock estimates. Careful characterization of constellation performance is necessary for the use of Advanced RAIM (ARAIM). In particular, the narrow (Psat) and wide (Pconst) fault rates must be determined. However, typical constellation monitoring approaches rely on the comparison between the broadcast ephemeris and precise estimates of the satellite orbit and clock, and these may not always be available. Furthermore, they may only monitor reference signals that will not actually be operationally used. This paper describes a method to independently estimate satellite clock and differential code biases in order to evaluate the ranging performance of GPS and GLONASS for ARAIM. Daily variations in the L1 C/A-L5Q clock and differential code bias are examined and quantified. Finally, GLONASS faults are closely examined using the clock estimation techniques.