Radio-based navigation systems usually consist of two parts. One of the parts is a receiving unit that analyzes the radio signals of multiple coded channels. Based on this data, it calculates its current position. Almost all of the popular GPS devices available today use the U.S. NAVSTAR GPS for position finding. The operating principle of these systems is based on Global Positioning System technology.
Computation of position is possible based on a minimum of three signals that are received. Without at least three signals, clock errors cannot be compensated for in the receiver. A fourth signal determines the altitude. If there are any additional satellite signals, this increases the precision of the calculation of location and results in the current position in longitude and latitude, with the highest accuracy within approximately ten meters. The system is completed usually by an electronic compass, which helps determine the position and the movement direction of the user. With the inclusion of the Doppler effect, a calculation of the current speed of the receiver is possible.
Navigation systems transmit this information today usually in a digital map format and can thus include not only the position coordinates, but also create a graphical, user-friendly image of the position on the digital map. The presence of maps in the navigation system gives the ability to render after entering the target coordinates of a route from the current location to your destination. It is not the direct distance between starting position and destination that is shown, but rather the route via roads, as they are displayed in the maps, which was determined by means of a so-called routing method. Thus it is possible to be guided by the navigation system in an unknown area to the target. The recommendations for the route is usually made by displaying on the screen and by spoken commands.
Calculating a route of transport via roads often results in a variety of possible routes to the destination, which places high demands on the system. Traffic conditions, such as bridges, one-way streets, dead ends, ferries or the like must be considered. Since different roads have different speed limits, the expected average speeds have to be accounted for on each route, which is almost always on offer on commercial navigation systems. Routes are calculated according to various criteria such as travel time or distance.