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Satellite navigation

A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). As of 2024, four global systems are operational: the United States's Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), China's BeiDou Navigation Satellite System (BDS),[1] and the European Union's Galileo.[2]

For maneuvering satellites to maintain orbit and station, see Orbital station-keeping.

Satellite-based augmentation systems (SBAS), designed to enhance the accuracy of GNSS,[3] include Japan's Quasi-Zenith Satellite System (QZSS)[3] and the European EGNOS, both based on GPS. Stand-alone operational regional navigation satellite systems (RNSS) include earlier generations of the BeiDou navigation system and the current Indian Regional Navigation Satellite System (IRNSS) or NavIC.[4]


Satellite navigation devices determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few centimeters to meters) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to a high precision, which allows time synchronisation. These uses are collectively known as Positioning, Navigation and Timing (PNT). Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.


Global coverage for each system is generally achieved by a satellite constellation of 18–30 medium Earth orbit (MEO) satellites spread between several orbital planes. The actual systems vary, but all use orbital inclinations of >50° and orbital periods of roughly twelve hours (at an altitude of about 20,000 kilometres or 12,000 miles).

GNSS-1 is the first generation system and is the combination of existing satellite navigation systems (GPS and GLONASS), with (SBAS) or Ground Based Augmentation Systems (GBAS).[5] In the United States, the satellite-based component is the Wide Area Augmentation System (WAAS); in Europe, it is the European Geostationary Navigation Overlay Service (EGNOS); and in Japan, it is the Multi-Functional Satellite Augmentation System (MSAS). Ground-based augmentation is provided by systems like the Local Area Augmentation System (LAAS).[5]

Satellite Based Augmentation Systems

GNSS-2 is the second generation of systems that independently provide a full civilian satellite navigation system, exemplified by the European Galileo positioning system. These systems will provide the accuracy and integrity monitoring necessary for civil navigation; including aircraft. Initially, this system consisted of only Upper L Band frequency sets (L1 for GPS, E1 for Galileo, and G1 for GLONASS). In recent years, GNSS systems have begun activating Lower L Band frequency sets (L2 and L5 for GPS, E5a and E5b for Galileo, and G3 for GLONASS) for civilian use; they feature higher aggregate accuracy and fewer problems with signal reflection.[6][7] As of late 2018, a few consumer-grade GNSS devices are being sold that leverage both. They are typically called "Dual band GNSS" or "Dual band GPS" devices.

[5]

GNSS systems that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:[5]


By their roles in the navigation system, systems can be classified as:


As many of the global GNSS systems (and augmentation systems) use similar frequencies and signals around L1, many "Multi-GNSS" receivers capable of using multiple systems have been produced. While some systems strive to interoperate with GPS as well as possible by providing the same clock, others do not.[8]

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Radiodetermination service

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Radiodetermination-satellite service

Radionavigation service

Maritime radionavigation service

Office for Outer Space Affairs of the United Nations (2010), .

Report on Current and Planned Global and Regional Navigation Satellite Systems and Satellite-based Augmentation Systems

ESA information on EGNOS

Information on the Beidou system

Global Navigation Satellite System Fundamentals