Current and Future GNSS and Their Augmentation Systems
Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geospatial positioning with global coverage. GNSS allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few meters using time signals transmitted along a line-of-sight by radio from satellites. Receivers on the ground, air, or water calculate the precise time as well as position, which can be used as a reference for scientific experiments and numerous everyday applications.
As of 2012, the Navstar Global Positioning System (GPS) of the United States and the Global Navigation Satellite System (GLONASS) of the Russian Federation are the only fully operational global GNSS. The European Union’s Galileo positioning system is a GNSS in the initial deployment phase, scheduled to be operational in 2014. The People’s Republic of China has decided to expand its regional BeiDou/Compass navigation system into a complete global navigation system by 2015 although, with 13 satellites in orbit, it already has limited global coverage. The global coverage for each system is generally achieved by a constellation of 24–30 Medium Earth Orbit (MEO) satellites distributed between several orbital planes. The actual systems vary, but use orbit inclinations greater than 50° and orbital periods of roughly 12 h (height 20,000 km / 12,500 miles). These global systems are being joined by the regional Quasi-Zenith Satellite System (QZZS) of Japan and the Indian Regional Navigation Satellite System (IRNSS) of India. These regional systems utilize satellites at smaller inclinations in elliptical orbits with apogees around 24,000 and 39,000 km or in inclined geostationary orbits at around 36,000 km. As accuracy in position, time, or speed measurements increases with the number of satellites that can be observed by a receiver, the signals received from the global from GNSS satellites are complemented by signals provided by satellite-based augmentations systems (SBAs). Such is the motivation for the Wide-Area Augmentation System of the United States, the System for Differential Correction and Monitoring (SDCM) of the Russian Federation, the European Geostationary Navigation Overlay Service (EGNOS), the GPS and Geo-Augmented Navigation system (GAGAN) of India, and the Multifunctional Transport Satellite (MTSAT) Satellite-based Augmentation System (MSAS) of Japan. Altogether, by 2020 there will be around 120 navigation and positioning satellites in orbit at any given moment. It is possible that a user could receive signals from as many at ten satellites, leading to accuracies only available at the research level today. This chapter presents the characteristics of all current and future generations of navigation and positioning satellites.
KeywordsGNSS GPS GLONASS Galileo Compass/BeiDou IRNSS QZSS WAAS SDCM EGNOS GAGAN MSAS Positioning Navigation and Timing (PNT) system Location Based Service Satellite-Based Augmentation System (SBA) Compatibility and Interoperability GNSS user services and policies Standard Positioning Service (SPS)
- D. Levin, “Chinese Square Off With Europe in Space”, The New York Times, 23 March 2009, http://www.nytimes.com/2009/03/23/technology/23iht-galileo23.html?_r=2%26scp=1%26sq=chinese%20europe%20galileo%26st=cse
- P. Marks, “ China’s Satellite Navigation Plans Threaten Galileo”, New Scientist, 08 November 2006, http://www.newscientist.com/article/dn10472-chinas-satellite-navigation-plans-threaten-galileo.html