GNSS augmentation

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Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as accuracy, 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 provide additional vehicle information to be integrated in the calculation process.

Satellite-based augmentation system[edit]

Service areas of satellite-based augmentation systems (SBAS).

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 DGPS.[1]

The GBAS and SBAS that have been implemented or proposed include:

Ground-based augmentation system[edit]

Each of the terms ground-based augmentation system (GBAS) and ground-based regional augmentation system (GRAS) describe a system that supports augmentation through the use of terrestrial radio messages. As with the satellite based augmentation systems detailed above, ground-based augmentation systems are commonly composed of one or more accurately surveyed ground stations, which take measurements concerning the GNSS, and one or more radio transmitters, which transmit the information directly to the end user from the ground up thus avoiding the constraints associated with GEO Satellites at high altitudes.

Generally, GBAS is localized, supporting receivers within 23 nautical miles, and transmitting in the very high frequency (VHF) band.

The shorter the distance between the ground station that calculates the differential corrections to the inbound plane, the higher the accuracy is likely to be. There are stricter Safety requirements on GBAS systems relative to SBAS systems since GBAS is intended mainly for the landing phase where real-time accuracy and signal integrity control is critical, especially when weather deteriorates to the extent that there is no visibility (CAT-I/II/III conditions) for which SBAS is not intended or suitable.[5]

Various ground-based augmentation systems[edit]

  • International Civil Aviation Organization Ground-Based Augmentation System (GBAS) applies to precision approach landing of civil aircraft. Originally this system was called the Local Area Augmentation System (LAAS)
  • The US Nationwide Differential GPS System (NDGPS), An augmentation system for users on U.S. land and waterways.[6]
  • See also, the Differential GPS (DGPS) Wikipedia page

Aircraft-based augmentation system (ABAS)[edit]

The augmentation may also take the form of additional information from navigation sensors being blended into the position calculation, or internal algorithms that improve the navigation performance. Many times the additional avionics operate via separate principles than the GNSS and are not necessarily subject to the same sources of error or interference. A system such as this is referred to as an aircraft-based augmentation system (ABAS) by the ICAO. The most widely used form of ABAS is receiver autonomous integrity monitoring (RAIM), which uses redundant GPS signals to ensure the integrity of the position solution, and to detect faulty signals.[7]

Additional sensors may include:

See also[edit]


External links[edit]