GNSS Augmentation

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

A Satellite Based Augmentation System (SBAS) is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages. Such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, the satellite signals, or other environmental factors which may impact the signal received by the users. Using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users.

While SBAS designs and implementations may vary widely, with SBAS being a general term referring to any such satellite-based augmentation system, under the International Civil Aviation Organization (ICAO) rules a SBAS must transmit a specific message format and frequency which matches the design of the United States' Wide Area Augmentation System.Fact|date=January 2007

Various Implementations

For details on how various SBAS are implemented, please see the following articles:
*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 European Space Agency.
*The Wide Area GPS Enhancement (WAGE), operated by the United States Department of Defense for use by military and authorized receivers.
*The Multi-functional Satellite Augmentation System (MSAS) system, operated by Japan's Ministry of Land, Infrastructure and Transport(JCAB).
*The commercial StarFire navigation system, operated by John Deere.
*The commercial Starfix DGPS System, operated by Fugro.
*The Quasi-Zenith Satellite System (QZSS), proposed by Japan.
*The GAGAN system, proposed by India.
*SIGI

Ground Based Augmentation System

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.

Generally, GBAS networks are considered localized, supporting receivers within 20km, and transmitting in the Very High Frequency (VHF) or Ultra High Frequency (UHF) bands. GRAS is applied to systems that support a larger, regional area, and also transmit in the VHF bands. [ [http://www.gnssapproach.com.au/pages/page152.asp GRAS advantages ] ]

Various Ground Based Augmentation Systems

* The United States' Local Area Augmentation System (LAAS)

Various Ground-based Regional Augmentation Systems

* Differential GPS (DGPS)

Additional Navigation Sensors

The augmentation may also take the form of additional information being blended into the position calculation. Many times the additional navigation sensors operate via a different principle 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 additional sensors may include:
* eLORAN receivers
* Automated Celestial navigation systems
* Inertial Navigation Systems
* Simple Dead reckoning systems (composed of a gyro compass and a distance measurement)

References

External links

* [http://www.gnssapproach.com.au/pages/index.asp Airservices Australia GBAS and GNSS website]