Parametric Performance Study of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) for Combined GNSS Constellations

Kurzfassung

GPS, Galileo and GLONASS are preparing for the transmission of signals in two protected frequency bands (L1, and L5). The combined use of such signals and the verification of their consistency significantly improve the autonomous integrity of position estimates. Aviation applications benefit from this increase in performance, and the use of GNSS as primary means of navigation for precision approach, e.g. in the LPV- 200 category, comes into reach. Previously considered integrity architectures heavily depend on augmentation, and have to respond within the time-toalert. Autonomous methods, such as the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) considered here, do not suffer from the latter constraint. However the threat space is significantly inflated: Simultaneous satellite faults as well as constellation faults need to be considered. This can be addressed by an ARAIM algorithm employing the principle of Multiple Hypothesis Solution Separation (MHSS), and limiting the threat space to faults with large probability. The present paper assesses the performance of this algorithm using combinations of future GNSS under different assumptions of satellite fault probability and constellation fault probability. Combinations of GPS, Galileo and GLONASS are investigated to determine the worldwide availability coverage using the integrity requirements defined in LPV-200: Vertical Protection Level (VPL), Effective Monitoring Threshold (EMT) and vertical positioning accuracy (Accv). Based on the simulation results presented here, combinations of GPS and Galileo are shown to provide sufficient VPL-based performance for LPV-200 precision approaches at all runways worldwide. However there exist limitations on meeting the EMT requirement if a single satellite is unavailable. Minimal dependence on the probability of satellite fault is observed for both VPL and EMT. With fault probabilities higher than 10^-3/approach, the LPV-200 availability requirement is not met. This probability threshold corresponds to approximately 40 observed faults per year for a nominal 27- SV constellation, with a 6-hour latency after fault onset. When using a triple GPS-Galileo-GLONASS constellation, the simulated performance becomes generally robust enough to handle even worst case scenarios without any degradation of the relevant performance metrics. However it is shown that assuming independent satellite fault events at high probabilities leads to high computational complexity with potential implications for the real-time capability of ARAIM. Thus, the current research results recommend a limitation on the total number of satellites used for processing integrity limits with MHSS ARAIM, possibly by employing a selection process to visible satellites from all available constellations.