Satellite Navigation
Global navigation satellite systems (GNSS) transmit satellite signals that can be used for location and navigation purposes around the world. The best known system is the Global Positioning System (GPS), which is operated by the US Government. Europe’s own global navigation satellite system Galileo is currently being set up, and will be available by 2011.
GNSS satellites transmit their precise position and time via radio waves. In order to locate, signals of at least three independent satellites have to be received simultaneously, and from these signals one’s own position can be ascertained by determining the time delay and by means of triangulation. Satellites are stationed in low-elevation orbits in order to receive signals with mobile devices. For physical reasons, their orbital speed is considerably higher than the rotational speed of the earth. Therefore, constellations of at least 24 – or, even better, 32 – satellites are necessary to receive signals of at least three – or, even better, four – satellites at any one location.
Assisted GNSS (A-GPS and A-Galileo) is an additional functionality to improve positioning accuracy and speed. The position is also determined by a GNSS receiver at a base station of a mobile radio system and is then passed on to the mobile phone via an assisted channel. Thus, telephones can quickly determine the new position, for example after switching the mobile phone on upon arrival at an airport.
