GNSS augmentation

Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place, and they are generally named or described based on how the GNSS sensor receives the external information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provides additional vehicle information to be integrated in the calculation process. Satellite-based augmentation systems (SBAS) support wide-area or regional augmentation through the use of additional satellite-broadcast messages. Using measurements from the ground stations, correction messages are created and sent to one or more satellites for broadcast to end users as differential signal. SBAS is sometimes synonymous with WADGPS, wide-area differential GPS. The GBAS and SBAS that have been implemented or proposed include: The Wide Area Augmentation System (WAAS), operated by the United States Federal Aviation Administration (FAA). The European Geostationary Navigation Overlay Service (EGNOS), operated by the ESSP (on behalf of EU's GSA). The Multi-functional Satellite Augmentation System (MSAS), operated by Japan's Ministry of Land, Infrastructure and Transport Japan Civil Aviation Bureau (JCAB). The Quasi-Zenith Satellite System (QZSS), operated by Japan, started initial operations in November 2018. QZSS also operates in a non-SBAS mode called PNT, essentially acting as extra GNSS satellites. The GPS-Aided GEO Augmented Navigation (GAGAN), operated by the Airports Authority of India. The System for Differential Corrections and Monitoring (SDCM), operated by Russia's Roscosmos. The BeiDou Satellite-Based Augmentation System (BDSBAS), proposed by China.