GALILEO Advanced RAIM Concepts

Use of GALILEO to support advanced RAIM concepts
Advanced Receiver Autonomous Integrity Monitoring (ARAIM) techniques, possibly aided by ground Integrity Support Messages (ISM), are currently receiving significant attention due to the prospects of good performance and lower infrastructure complexity when applied to the case of many satellites with dual-frequency signals, as it will be the case for GNSSs like GPS and Galileo. The concept of ISM shall cover the overall architecture to support integrity for ARAIM, thus be including the relevant ground infrastructure, the processing and the dissemination of the data information.
Today, aviation integrity services over regional areas rely to a considerable extent on satellite based information (SBAS), based on the single-frequency GPS open services, and require the broadcasting of satellite and ionospheric corrections. Apart from SBAS, RAIM integrity can also be used however limited to en-route phases of flight without vertical guidance and NPA procedures.
The SBAS services are internationally adopted by ICAO, and are regionally implemented by different systems including WAAS and EGNOS. The SBAS infrastructure is responsible of protecting the user from the possible GNSS system and satellite failures, and of informing the user within few seconds.
SBAS systems functions are considerably complex. These functions include, the collection of measurements from a dense continental network of complex sensor stations, the computation and GEO broadcasting in quasi real-time of orbit+clock corrections, the computation and GEO broadcasting in quasi real-time of ionospheric corrections, integrity error bounds for the orbit+clock and ionospheric corrections, and the computation and GEO broadcasting in real-time of integrity flags.
Actual SBAS physical architecture, implementing the above SBAS system functions, is subject to very demanding accuracy, integrity, continuity and availability requirements, implying numerous redundancies, as well as numerous architecture components with very demanding design assurance levels. The project addresses also these aspects.