Analysis of Use of Receiver Autonomous Integrity Monitoring (RAIM) in a GPS Wide-Area Augmentation System (WAAS),

Among different augmentation alternatives for Required Navigation Performance RNP use of GPS, a GPS Wide Area Augmentation System WAAS could provide precision approach capability over a wide geographic area with a single system. Currently, the FAA is sponsoring research to determine how to make the WAAS concept satisfy RNP requirements for precision approach. Integrity is especially important because it has a direct impact on safety over a wide area. In order to improve integrity beyond the level provided by the ground segment of the system and to guarantee required local accuracy, use of receiver autonomous integrity monitoring RAIM in conjunction with the WAAS system may be advantageous. Should RAIM be used, there are questions regarding its availability. The paper analyzes availability of RAIM and availability of navigation when an alternative WAAS integrity concept called VMAX is used. The analyses show that while the availability of navigation with the VMAX concept is higher than the availability of RAIM, neither one meets stringent WAAS RNP availability requirements. These results point to the need to analyze alternative concepts.