GF82.61-P-3007SKJ Global Positioning System(GPS) Position Finding, Function

GF82.61-P-3007SKJ Global Positioning System(GPS) Position Finding, Function
- with CODE (498) Japan version







The global positioning system (GPS) is a satellite-supported localizing system set up by the American Department of Defense. It is a toll-free service available throughout the world. There are several satellites on different orbits around the earth. The GPS satellites constantly transmit time and position data.
4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient. GPS position finding is irreplaceable for journeys outside the digitized map area and after vehicle transport (e.g. train or ferry journeys and towing). A new GPS position (after interruption of the satellite reception) can take several minutes ( up to 20 minutes when the equipment is first set up).

GPS position finding, function
The navigation processor in the COMAND operating, display and control unit (A40/3) calculates the vehicle location and the exact position from the satellite signals received and amplified by the GPS antenna (A2/23).

The actual calculation is essentially based on the measurement of the travel times of the signals sent synchronously by the various satellites. Here, an important prerequisite is that the satellite and receiver clocks are synchronized . For this purpose, the receiver has an automatic time correction feature which again is possible with the aid of the satellite signals.
If the navigation processor of the COMAND operating, display and control unit (A40/3) determines that the basic position finding (dead reckoning) is less accurate than GPS position finding, the currently calculated position is corrected with the aid of the GPS data. In addition, the vehicle's course of travel is determined with the aid of the sequence of the locations calculated with GPS.

Approximately 50 GPS recalculations of the location take place per minute.

Possible interference when receiving GPS signals
Since GPS operates in the Gigahertz (GHz) range (microwaves) and the signals are weak, reception interference can occur as a result of:
^ Atmospheric interference
e.g. bad weather, water vapor, fog
^ Multipath reception due to the reflection of the signals,
e.g. from house walls
^ Signal shading
e.g. in built-up areas, in tunnels, by high buildings and by trees

GPS reception therefore necessitates a clear view of the sky. Positioning accuracy is approx. 100 m.