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

GF82.61-P-3007QM Global Positioning System(GPS) Position Finding, Function
- with CODE (527) COMAND APS (with navigation)







GPS is a satellite-supported localizing system set up by the US Department of Defense. It is a toll-free service available throughout the world. Various 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).

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

GPS position finding, function
The navigation processor in the COMAND operating, display and control unit (A40/3) calculates the vehicle location and the accuracy from the satellite signals received and amplified by the GPS antenna (A2/23).
The actual calculation is based significantly on the measurement of the transmission times of the signals transmitted 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. When the navigation processor determines that the basic location finding is less precise than GPS location finding, the current 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.

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 the result of:
^ Atmospheric interference,
e.g. weather, water vapor, fog
^ Multiple reception from reflection of signals,
e.g. from building walls
^ Signal shadows,
e.g. in built-up areas, tunnels, from tall buildings, from trees

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