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

GF82.61-P-3007SK Global Positioning System(GPS) Position Finding, Function
- with CODE (525) MB Audio 50 APS radio
- with CODE (527) COMAND APS with single DVD drive (with navigation)







The navigation processor of the radio and navigation unit (A2/56) with code (525) Audio 50 APS MB radio is integrated into the control unit. With the COMAND operating, display and controller unit (A40/3) with code (527a) COMAND APS (with navigation), the external navigation module is designated as navigation processor (N41/1).

The global positioning system (GPS) is a satellite-assisted position finding system set up by the US Department of Defense. It is free and available worldwide. Several satellites are on different orbits around the earth. The GPS satellites permanently transmit time and position data.
4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient. The GPS position finding is, in particular, for journeys outside the digitized map area and after transportation of the vehicle (e.g. train, ferry and towing) irreplaceable.

Starting GPS position finding again (following interruption of the satellite reception) may take several minutes (for initial startup of the device up to 20 min).

GPS position finding, function
The navigation processor (N41/1) calculates the vehicle location and the accuracy of the locating from the amplified satellite signals received by the GPS antenna (A2/23).
The actual calculation is essentially based on the measurement of the runtimes of the signals transmitted synchronously by the various satellites. An important requirement here is the synchronicity of the clocks for the satellites and the receiver. To this end the receiver is equipped with an automatic time correction, which in turn is made possible with the aid of the satellite signals.
If the navigation processor (N41/1) determines that the basic position finding is less precise than the GPS position finding, the currently calculated position is corrected using the GPS data.

In addition to this the sequence of locations calculated by the GPS is used to determine the vehicle's route.

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

Possible interference when receiving GPS signals
As GPS operates in the GHz range (microwaves) and the signals are weak, reception interference may occur due to:
^ Atmospheric interference,
e.g. weather, water vapor, fog
^ Multi-path reception due to signal reflections,
e.g. from building walls
^ Interruption of signal reception,
e.g. in areas with superstructures and in the vicinity of tunnels, tall buildings, trees

GPS reception therefore necessitates a clear view of the sky. The accuracy of GPS location finding is approx. 100 m or better.