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

GF82.61-P-3007RM Global Positioning System(GPS) Position Finding, Function
- Model 230.474/475
- with CODE (527) COMAND APS (with navigation)







GPS position finding, function
The navigation processor (N41/1) calculates the vehicle location and the accuracy of the locating from the amplified satellite signals received 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 navigation processor (N41/1) determines that the basic position finding (dead reckoning) is less precise than the GPS position finding, the currently calculated position is corrected using 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 GPS is a satellite-supported localizing system installed by the American Department 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 minutes when the equipment is first set up).

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

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
^ Multipath reception due to the 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 proper GPS reception, no obstruction may be located between the GPS antenna (A2/23) and the satellite. Positioning accuracy is approx. 100 m.