Global positioning system (GPS) position finding, function - GF82.61-P-3007T
MODEL 211.0 /2 up to 31.5.06 with CODE (525) MB Audio 50 APS radio with CODE (527) Navigation module for COMAND
Shown on model 211.0
The global positioning system (GPS) is a satellite-assisted position finding system set up by the US Department of Defense. It is a toll-free service available throughout the world. The GPS satellites constantly transmit time and position data.
Four satellites are required for the initial calculation of the position, after that three 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 for the radio control panel and navigation unit (A2/56), with code (525) MB Audio 50 APS radio, is integrated into the operating unit. With the COMAND operating, display and control unit (A40/3), with code (527) COMAND APS (with navigation), the external navigation module is referred to as a navigation processor (N41/1).
GPS position finding, function
The navigation processor (N41/1) calculates the vehicle location and the accuracy of the positioning from the satellite signals received and amplified by the GPS antenna (A2/49a2) (model 211.0) or from the GPS antenna (A2/23) (model 211.2).
The actual calculation is essentially based on the measurement of the travel times of the signals sent synchronously by the various satellites. An important prerequisite for this is the synchronicity of the clocks, the satellites and the receiver.
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 (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. Moreover, the route of the vehicle is determined from the sequence of locations calculated with GPS.
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. Positioning accuracy is approx. 100 m.
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