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

MODELS 203.0 /2 /7 up to 23.4.04 with CODE (352a) COMAND operating and display system with CODE (491) U.S. version 

Position finding by Global Positioning System (GPS) 

Function 

The global positioning system (GPS) is a satellite-supported position finding system set up by the American Department of Defense. It is a toll-free service available throughout the world. Presently several satellites are located in various orbits. 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).

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 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. 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.

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

Possible interference when receiving GPS signals 

Since GPS operates in the Giga Herz (GHz) range 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 shadowing,

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

GPS reception therefore necessitates a clear view of the sky. Positioning accuracy is approx. 100 m.

	Operating, display and control unit, location/ task/design/function		GF82.85-P-3114R
	Basic position finding, function		GF82.61-P-3006R
	Map-based position finding, function		GF82.61-P-3008R
	Destination guidance, function		GF82.61-P-3012R
	Global positioning system antenna, location/ task		GF82.61-P-4107P