Global positioning system (GPS) position finding, function - GF82.61-P-3007PM

MODEL 203.0 /2 /7 as of 24.4.04 with CODE (527) COMAND APS with single DVD drive (with navigation) 

Position finding using Global Positioning System (GPS) 

GPS position finding, function 

The navigation processor in the COMAND operating, display and control unit (A40/3) calculates the vehicle location and the exact position from the satellite signals received and amplified by the GPS antenna (A2/23).

The actual calculation is based on the measurement of the transmission times of the signals transmitted 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. When the navigation processor determines that the basic location finding is less precise than GPS location finding, the current calculated position is corrected with the aid of 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.

GPS is a satellite supported localizing system set up by the US Department of Defense. It is a toll-free service available throughout the world. The various 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).

The location is recalculated approx. 50 times per minute by the GPS system.

Possible interference when receiving GPS signals 

Since GPS operates in the gigahertz range (microwaves) and the signals are weak, reception interference can occur as the result of:

• Atmospheric interference,

  e.g. weather, water vapor, fog

• multiple reception from reflection of signals,

  e.g. from building walls

• Signal blocking,

  e.g. in densely populated areas, tunnels, high-rise buildings, trees

GPS reception therefore necessitates a clear view of the sky. The location accuracy is approx. 100 m and less.

Operating, display and control unit, location/task/design/function

GF82.85-P-3114PM