SBAS (Satellite-Based Augmentation System)

A satellite-based augmentation system, or SBAS, improves a core GNSS such as GPS by broadcasting wide-area differential corrections and integrity messages from geostationary satellites on the GNSS L1 frequency. The regional systems are WAAS over North America, EGNOS over Europe, and MSAS over Japan. A network of ground reference stations measures satellite clock, ephemeris, and ionospheric errors; a master station computes a correction grid and uplinks it to the GEO satellites, which relay it to any SBAS-capable receiver. The integrity message warns a user within about six seconds if a satellite should not be used, the safety-of-life feature plain GPS cannot supply.