EARTH ORIENTATION PARAMETER FAULT MONITOR FOR HIGH INTEGRITY GNSS AVIATION APPLICATIONS

This paper develops threat models and mitigation techniques for mutually consistent satellite faults that are not detectable using Advanced Receiver Autonomous Integrity Monitoring (ARAIM) methods but are potentially hazardous to aviation users. Faults in the generation of Earth Orientation Parameters (EOPs), EOP Predictions (EOPPs) and their subsequent processing by the GPS Operational Control Segment (OCS) are of particular interest. In principle, if such faults are not detected by OCS, GPS satellite ephemerides could be corrupted constellation-wide in a consistent way, rendering existing ARAIM algorithms ineffective. The initial credibility of the EOP threat is established by the fact that it is explicitly listed as a potential integrity failure mode in the current GPS Standard Positioning Service Performance Standard (GPS SPS). Additionally, an observed EOP fault occurred on June 17, 2012. The dynamics of EOP faults can be reliably modeled as an initial bias with additive linear time variations. An initial broadcast ephemeris (A) is assumed to be EOP fault free and is verified as such via a ground monitor. If the second ephemeris (B) contains an EOP fault, then all satellite positions computed using ephemeris (B) would be rotated with respect to satellite positions obtained from ephemeris (A). Using the difference between the two computed satellite positions as the monitor 'measurement' in conjunction with the dynamic fault model, the parameters defining the EOP fault can be estimated using weighted least squares estimation. The two monitor components (airborne and ground) are bridged together by an Integrity Support Message (ISM). The ISM is needed to provide airborne users with essential information to bound nominal error distributions and fault prior probabilities. xiii The ISM also provides a means to inform airborne users of which ephemerides have passed civil ground monitor validation. The frequency of ISM updates needed to protect airborne GNSS users from the EOP threat is specified. Finally, global availability analysis show that the inclusion of the EOP fault detection algorithms does not cause any availability loss for LPV-200 aircraft precision approach applications.M.S. in Mechanical and Aerospace Engineering, May 201