Global positioning system (GPS) position finding, function with code 525 and 527 - GF82.61-P-3007SK
MODEL 171.4 with CODE (525) MB Audio 50 APS radio
MODEL 171.4 with CODE (527) COMAND APS with single DVD drive (with navigation)
Location finding with GPS
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. On the COMAND operating, display and control module (A40/3) with code (527a) COMAND APS (with navigation) the external navigation module is called 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 a tollfree service available throughout the world. 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).
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 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 (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, 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 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.
| Operating, display and control module, location/purpose/design/function | GF82.85-P-3114SK |
| GPS antenna, location/purpose | GF82.62-P-4107SK |
| Navigation processor, location/purpose/ design/function | GF82.85-P-3103SK |