Detailed Analysis of Raim Performance for ADS‐B Separation Error

Performance standards are currently being developed for GPS-based Automatic Dependent Surveillance Broadcast (ADs-B). Of concern is the possibility of significant error in apparent aircraft separation when the ADS-B position reports are based on slightly different sets of satellites, but a fault on a common satellite goes undetected by RAIM algorithms in both aircraft. Performance of solution-separation RAIM in the above circumstance is analyzed in depth. Dependence of the conditional separation error risk on the correlation between the two RAIM decision statistics is derived in detail. The total risk (including the prior probability of satellite fault) is evaluated to compare RAIM-based ADS-B performance with current surveillance radar for achieving the 3.0 nmi separation standard in the terminal area. The analysis considers two prospective values (0.5 nmi and 0.6 nmi) of the RAIM Horizontal Alert Limit (HAL) corresponding to the radius of containment (R c ) associated with ADS-B position reports.