GNSS Augmentation
Encyclopedia
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.
Generally, GBAS networks are considered localized, supporting receivers within 20 km, 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.
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 additional sensors may include:
Global Navigation Satellite System
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from...
(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
Clock drift
Clock drift refers to several related phenomena where a clock does not run at the exact right speed compared to another clock. That is, after some time the clock "drifts apart" from the other clock. This phenomenon is also used for instance in computers to build random number generators...
, ephemeris
Ephemeris
An ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...
, 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.Implementations
For details on how various SBAS are implemented, please see the following articles:- The Wide Area Augmentation SystemWide Area Augmentation SystemThe Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
(WAAS), operated by the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
Federal Aviation AdministrationFederal Aviation AdministrationThe Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA). - The European Geostationary Navigation Overlay ServiceEuropean Geostationary Navigation Overlay ServiceThe European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals...
(EGNOS), operated by the European Space AgencyEuropean Space AgencyThe European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
. - The Wide Area GPS EnhancementWide Area GPS EnhancementWide Area GPS Enhancement is a method to increase the horizontal accuracy of the GPS encrypted P Code by adding additional range correction data to the satellite broadcast navigation message....
(WAGE), operated by the United States Department of DefenseUnited States Department of DefenseThe United States Department of Defense is the U.S...
for use by military and authorized receivers. - The Multi-functional Satellite Augmentation SystemMulti-functional Satellite Augmentation SystemMulti-functional Satellite Augmentation System is a Japanese SBAS , i.e. a satellite navigation system which supports differential GPS designed to supplement the GPS system by reporting on the reliability and accuracy of those signals...
(MSAS) system, operated by JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
's Ministry of Land, Infrastructure and Transport (JCAB). - The commercial StarFire navigation systemStarFire (navigation system)StarFire is a wide-area differential GPS developed by John Deere's NavCom and precision farming groups. StarFire broadcasts additional "correction information" over satellite L-band frequencies around the world, allowing a StarFire-equipped receiver to produce position measurements accurate to well...
, operated by John DeereDeere & CompanyDeere & Company, usually known by its brand name John Deere , is an American corporation based in Moline, Illinois, and the leading manufacturer of agricultural machinery in the world. In 2010, it was listed as 107th in the Fortune 500 ranking...
. - The commercial Starfix DGPS System and OmniSTAROmniSTAROmniSTAR is a wide-area differential GPS service provider. OmniSTAR correction signals are proprietary, and a subscription must be bought from the OmniSTAR corporation to receive a subscription authorization....
system, operated by FugroFugroFugro N.V. is a Dutch multinational company headquartered in Leidschendam. The current president is K.S. Wester.Fugro provides geotechnical, survey and geoscience services to oil, gas, mining and construction industries...
. - The Quasi-Zenith Satellite System (QZSS), proposed by Japan.
- The GAGANGPS Aided Geo Augmented NavigationThe GPS aided geo augmented navigation or GPS and geo-augmented navigation system is a planned implementation of a regional satellite-based augmentation system by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals.The Rs...
system, proposed by IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. - The Satellite Navigation Augmentation System(SNAS),proposed by China.
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 20 km, and transmitting in the very high frequency
Very high frequency
Very high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
(VHF) or ultra high frequency
Ultra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
(UHF) bands. GRAS is applied to systems that support a larger, regional area, and also transmit in the VHF bands.
Various ground-based augmentation systems
- The United States' Local Area Augmentation SystemLocal Area Augmentation SystemThe Local Area Augmentation System is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a central location at the airport. This data is used to formulate a correction message, which...
(LAAS)
Additional navigation sensors
The augmentation may also take the form of additional information being blended into the position calculation. Many times the additional avionicsAvionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
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 additional sensors may include:
- eLORAN receivers
- Automated Celestial navigationCelestial navigationCelestial navigation, also known as astronavigation, is a position fixing technique that has evolved over several thousand years to help sailors cross oceans without having to rely on estimated calculations, or dead reckoning, to know their position...
systems - Inertial Navigation SystemInertial navigation systemAn inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...
s - Simple Dead reckoningDead reckoningIn navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...
systems (composed of a gyro compass and a distance measurement)