Location finding, global positioning system, function - GF82.61-P-3007D

MODEL 208, 210 with CODE (352a) COMAND operating and display system 

The global positioning system (GPS)  is a satellite-supported location finding system established by the US defense department  . It is not subject to fees and is available worldwide. 26 satellites are currently orbiting the earth on different trajectories  . The GPS satellites continuously transmit time and position data.

For initially calculating the position four satellites are required, then reception of three satellites is sufficient.

GPS location finding is particularly valuable when driving outside of the digitized map area and following vehicle transport (e.g. train, ferry or towing).

Repeated GPS location finding (following satellite reception interruption) can take several minutes (when the unit is initially started up to 20 minutes)  .

GPS map matching function 

The navigation processor  of the COMAND operating, display and control module (A40/3)  calculates the vehicle location and the precise location finding from the satellite signals received and amplified by the GPS antenna (A2/23)  .

The actual calculation is based primarily on the measurement of the transmission times of the signals transmitted synchronously by the various satellites. This requires that the clocks in the satellites and the receiver be synchronized with one another.

For this purpose the receiver is equipped with an automatic time correction feature which is possible with the aid of the satellite signals. If the navigation processor  determines that the basic location finding is less precise than the GS location finding  the currently calculated position is corrected with the aid of the GPS data  .

Moreover, the course of travel is determined from the sequence of the locations calculated with GPS  .

The GPS location is recalculated approx. 50 times per minute.

Possible interference when receiving GPS signals 

Since GPS  operates in the GHz range  (microwaves) and the signals are weak, this could lead to the following reception interferences  :

• Atmospheric interferences, 

  e.g. weather, water vapor, fog.

• Multiple path reception  from reflected signals

  e.g. house walls

• Signal shadowing, 

  e.g. in built-up areas, tunnels, high buildings, trees.

A free view of the sky is therefore necessary for GPS reception  .

Positioning accuracy is approx. 100 m  or higher.

Basic location finding, function	GF82.61-P-3006E
Map-supported location finding, function	GF82.61-P-3008D
Route guidance, function	GF82.61-P-3012E
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