GF82.61-P-3007PP Global Positioning System(GPS) Position Finding, Function

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







Global positioning system, position finding, function
The global positioning system (GPS) is a localizing system established by the US Defense Department and is satellite supported. It is a toll-free service available throughout the world. 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)
Following interruption of the satellite reception, a new GPS position finding operation can take several minutes (up to 20 minutes when the equipment is first set up).

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.

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 interference,
e.g. weather, water vapor, fog
^ Multiple reception resulting 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.