GF82.61-P-3007GH Position Finding, Global Positioning System, Function

GF82.61-P-3007GH Position Finding, Global Positioning System, Function
- with CODE (352a) COMAND operating and display system
- except CODE (491) U.S. version
- except CODE (498) Japanese version







General
The global positioning system (GPS) is a satellite-supported location finding system. It is toll free worldwide. At the and available present time there are 26 satellites in different 6 earth orbits. The GPS satellites constantly transmit time and position data. If data from at least 3 satellites (for two dimensional position findings) is received, then the position of the receiver can be computed. The GPS position finding is particularly valuable when driving outside of the digitized map area and following vehicle transport (e.g. train, ferry or towing).

A repeated GPS position finding (following satellite reception interruption) can take several minutes (when the device is initially started up to 20 minutes).

GPS map matching function
The navigation computer bases its computation on the satellite signals received and amplified from the CTEL and GPS roof antenna (A2/49). These are distributed by the CTEL and GPS antenna splitter (A2/57) , in order to determine the position of the vehicle and to verify the position finding accuracy. The actual computation is essentially based on the measurement of the operating times of the signals transmitted synchronously from 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 computer calculates that the basic position finding is not as accurate as the GPS position finding, then the current computed position is corrected with the aid of the GPS data.

Moreover, the vehicle's route is calculated using the GPS sequence of positions.

During this time, roughly 50 GPS recalculations of the position are performed every minute.

Possible interference when receiving GPS signals
As GPS operates in the GHz range (microwaves) and the signals are weak, reception interference may occur through:
- atmospheric interference,
e.g. weather, water vapor, mist
- multiple reception through reflections of the signals,
e.g. on building walls
- signal shadows,
e.g. in densely built-up areas, tunnels, high-rise buildings, trees

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