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

GF82.61-P-3007QMU Global Positioning System(GPS) Position Finding, Function
- with CODE (530) COMAND APS USA (with navigation system)







Function
The Global Positioning System (GPS) is a satellite-assisted localizing system set up by the American Ministry of Defense. It is a toll-free service available throughout the world. Currently several satellites are 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).

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 determines that the basic position finding (dead reckoning) is less accurate than GPS position finding, then the position currently calculated is corrected using 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.

Every minute, approximately 50 GPS recalculations of the location take place.

Possible interference when receiving GPS signals
As the GPS operates in the Giga Hertz range (GHz) and the signals are weak, reception faults can occur due to the following events:
^ atmospheric interference,
e.g. weather, water vapor, fog
^ Multipath reception due to the reflection of the signals
e.g. from walls of buildings
^ Signal shading,
e.g. in built-up areas, in tunnels, due to tall buildings, due to trees

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