GPS stands for Global Positioning System and it is a satellite-based navigation system. Originally developed for military purposes, it is today used for many civilian applications such as vehicle navigation, emergency location services or for outdoor navigation by hikers and cyclists.
A GPS device requires an unobstructed line of sight to four or more GPS satellites in order to ascertain its own position. The more satellites in the line of sight, the faster position and speed can be determined. Since GPS devices only receive but don’t send data, no location data information is transmitted to third parties. The data signal is transmitted at a rate of 50 bits per second with a 30-second frame using the spread spectrum technique on the frequencies of 1575.42 MHz and 1227.60 MHz. A third civil frequency, 1176.45 MHz, is currently being implemented to further improve reception robustness. It will primarily be used by the aviation industry and for emergency services applications.