Date Added: Jul 2012
Global Navigation Satellite Systems (GNSS) is the general concept used to identify those systems that allow user positioning and timing based on a constellation of satellites. Specific GNSSs are the well-known American GPS, the Russian GLONASS or the forthcoming European Galileo. All those systems rely on the same principle: the user computes its position by means of measured distances between the receiver and the set of in-view satellites. These distances are calculated estimating the propagation time that transmitted signals take from each satellite to the receiver. Now-a-days, GPS (often combined with an augmentation system) is used in a myriad of applications such as geodesy and surveying, Earth observation, piloted and autonomous aircraft landing, or distributed synchronization of radio communication links and electric power networks.