Current and Future GNSS and Their Augmentation Systems

Abstract

Global Navigation Satellite System (GNSSs) 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.

Currently, the Navstar Global Positioning System (GPS) of the United States, the Global Navigation Satellite System (GLONASS) of the Russian Federation, and the People’s Republic of China BeiDou/Compass navigation system are the three 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 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 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 as 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.