Protecting Against Receiver Faults to a PPP Ground-Based Integrity Monitor System

It is shown (Lai et al., 2024a) that the Integrity Monitor System (IMS) can monitor and detect multiple clock and ephemeris faults happening at the same time using single centralized fault-tolerant filter with a groud-based reciever network. However, there is no guarantee that all the receivers of the monitor network are always correct. We cannot rule out the possibility of receiver faults if we want to use measurements from receivers to monitor the integrity of the clock and ephemeris corrections from PPP service. That is, the integrity of the IMS itself also needs to be protected. For this reason, we consider receiver faults when assessing the integrity of the overall system in this paper. To account for the receiver faults in IMS when estimating the ephemeris and satellite clock bias errors, we apply Solution Separation (SS) for measurements from different receivers to detect the potential receiver fault and place an upper bound on the maximum undetected errors in terms of User Range Errors (UREs). This is similar to what Advanced Receiver Autonomous Integrity Monitoring (ARAIM) does on detecting satellite faults. We form a number of subset filters with each of it excluding certain combination of receivers to form subset solutions. In this case, the statistics to be compared of is the errors from All-In-View (AIV) and subset solutions. By evaluating the differences of UREs between AIV and subset solutions, we can compute for the upper bound of the UREs that take into account the receiver fault modes. The upper bounds can then be approximated as a normal distribution that overbounds the UREs that includes ephemeris, satellite clock and receiver fault modes that the users can reference to protect the integrity.