RAIM in dual frequency / multi constellation APV/LPV operations in aeronautics

In aeronautics, Receiver Autonomous Integrity Monitoring (RAIM) techniques based on GPS L1 measurements are currently used in En-route and NPA operations, but not in those that require vertical guidance (APV operations/LPV procedures like LPV200). For these phases of flight SBAS, GBAS or classical ILS navaids are used because they offer better performance than GPS RAIM. However, in future RAIM performance is expected to improve significantly due to the deployment of new GNSS constellations in addition to GPS and a second frequency (L5) protected for use in aviation. The former will result in more satellites being available to the user and the latter will enable ionosphere delays to be corrected for autonomously onboard. Therefore, it is envisaged that RAIM will play a significant role in APV operations in the future. This paper highlights the possible role for multi constellation RAIM techniques in APV operations and identifies their advantages and limitations. The candidate algorithms are then reviewed in detail and conclusions drawn on their potential and future research.