GNSS

The Global Navigation Satellite System (GNSS) is a constellation of satellites, transmitting signals used for several types of navigation and positioning applications, anywhere on the surface of the earth. There are currently two Global Navigation Satellite Systems in operation: the U.S. Global Positioning System (GPS) and the Russian Global Navigation Satellite System (GLONASS). A third system, Galileo, is currently being developed in Europe. Galileo will provide a wide range of positioning signals and services including high-reliability service required by safety-of-life-critical applications. High level of integrity will be provided on the global scale and without any additional augmentation system. All the three systems will be interoperable. Combined use of Galileo and GPS will provide unprecedented increase in the availability of positioning.

Another name for GPS (Global Positioning System) given by its owner, the U.S. Department of Defense, is NAVSTAR (Navigation Satellite Timing and Ranging). GPS  is a satellite based navigation system, operational since late 1995. Its constellation consists out of 24 satellites, which transmit ranging signals and navigation data 24 hours a day free of charge . GPS receivers obtain their locations on earth by measuring the distance from the satellites and computing their position relative to the Earth-fixed coordinate frame, WGS-84. GPS is funded and controlled by the U.S. Department of Defense (DoD) and was originally intended for military applications. In the 1980s, the U.S. government made the GPS system available for civilian use. It was the first system widely available to civilian users.

The Russian Global Navigation Satellite System GLONASS is similar in operation as GPS and may prove complimentary to the NAVSTAR system. Launched in 1996, its constellation is orbiting 19,100 Km above the earth in three orbital planes.

The development of the European GNSS system, GALILEO, began in 1999. It is scheduled to be fully operational in 2008. In its full constellation, Galileo will consist of 30 satellites, continuously transmitting high-frequency ranging signals, containing time and distance data to be tracked by a Galileo receiver. The future Galileo satellites will transmit a variety of signals modulated on four different carriers: E5a, E5b, E6 and L1. New signal processing techniques are required in order to track Galileo signals due to the new modulation types BOC and AltBOC and the presence of Pilot and Data channels at all frequencies. Galileo will provide a wide range of services including open, safety-of-life, commercial, and publicly-regulated service. Galileo will guarantee the reliability of its signal anywhere on earth.