An Efficient Fault Detection and Exclusion Method for Spatial Gradient Monitors

With multiple ground reference stations, the double differenced carrier phase (DDCP) observation can be used to detect a faulty satellite caused by ephemeris fault or ionospheric anomaly, taking advantage of the residual spatial gradient. Assuming only a single satellite can be faulty at a time, it is necessary to distinguish whether a fault comes from a reference satellite (RS) or a non-reference satellite (NRS) in a single DDCP test. Using the current fault detection and exclusion (FDE) method of ephemeris faults in ground-based augmentation system, before an NRS can be tested in real-time by the DDCP, an RS is pre-validated using the previous ephemeris for the newly acquired and re-acquired satellites. This method lacks theoretical support, and the outcome test risks are not obtained. Also, for an ionosphere anomaly, the pre-validation method is not applicable anymore. Considering that existing test theories are designed to test single satellite in one test statistics, this paper proposes an efficient FDE method to test both RS and NRS simultaneously in real-time for both ephemeris fault and ionosphere anomaly. To facilitate application of the new method for purpose of integrity monitoring, the test risks and protection level are bounded.