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

GF82.61-P-3007RJ Global Positioning System(GPS) Position Finding, Function
- with CODE (498) Japan version







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. If the integrated navigation processor determines that basic position finding (dead reckoning) is less accurate than GPS position finding, then the current calculated position is corrected using 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 GPS is a satellite-assisted localizing system that has been set up by the American Ministry of Defense. It is a toll-free service available throughout the world. 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 min. when the equipment is first set up).

Every minute, approximately 50 GPS recalculations of the location take place.

Possible interference when receiving GPS signals
As GPS operates in the gigahertz (GHz) range (microwaves) and the signals are weak, reception interference may occur due to:
^ atmospheric interference,
e.g. bad weather, water vapor, fog
^ Multiple reception due to reflection of the signals,
e.g. from walls of buildings
^ Signal shading,
e.g. in built-up areas, tunnels, through high buildings, through trees

For GPS reception purposes there must be no obstacles between the GPS antenna (A2/23) and the satellites. Positioning accuracy is approx. 100 m.