GNSS augmentation

GNSS augmentation is a method of improving the satellite 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; "state-space representation"), others provide direct measurements of how much the signal was off in the past (differential GPS; "observation-space representation"), while a third group provides additional vehicle information to be integrated in the calculation process (sensor fusion).