Global positioning system (GPS) location finding, function - GF82.61-P-3007TU
MODEL 211.0 /2 up to 30.6.06 with CODE (528) HIGH Class USA
Shown on model 211.0
The Global Positioning System (GPS) is a satellite-assisted localizing system set up by the US Defense Ministry. It is toll-free and is available throughout the world. Currently several satellites are on six different orbits of the earth. The GPS satellites send time data permanently.
Four satellites are required for the initial calculation of the position, then 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 location (after interruption of the satellite reception) can take several minutes (when the equipment is first commissioned up to 20 minutes).
With code (527) navigation module for COMAND and code (528) HIGH Class USA the external navigation module is designated navigation processor (N41/1).
GPS map matching function
The navigation processor (N41/1) calculates the vehicle location and accuracy of location (A2/49a2) from the satellite signals received and amplified by the GPS antenna.
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.
The location is recalculated approx. 50 times per minute by the GPS system.
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 disturbances such as weather, water vapor, mist
- Multipath reception due to signal reflections, such as on house walls
- Signal shadowing e.g. in built up areas and near tunnels, high buildings, trees
GPS reception therefore necessitates a clear view of the sky. The accuracy of GPS location finding is approx. 100 m or better.
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