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

MODEL 211.0 /2 with CODE (529) HIGH Class Japan

Global positioning system (GPS) position finding

Fig 1: View Of GPS Satellite Position Finding

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

General

The GPS is a satellite-assisted positioning system that has been set up by the US Ministry of Defense. It is free and available worldwide. The GPS satellites permanently transmit time and position data.

4 satellites are needed for the first position calculation, then 3 receivable satellites are sufficient.

The GPS position finding is, in particular, for journeys outside the digitized map area and after transportation of the vehicle (e.g. train, ferry and towing) irreplaceable.

Starting GPS position finding again (following interruption of the satellite reception) may take several minutes (for initial startup of the device up to 20 min).

Function

The navigation processor uses the satellite signals received and amplified by the GPS antenna (A2/23) (model 211.2), by the GPS antenna (A2/49a2) (model 211.0) for vehicles up to 30.6.06 or by the GPS antenna (A2/49a2) for vehicles as of 1.7.06 to calculate the vehicle location and to determine the accuracy of the positioning.

The actual calculation is essentially based on the measurement of the runtimes of the signals transmitted synchronously by the various satellites. An important requirement here is the synchronicity of the clocks for the satellites and the receiver. To this end the receiver is equipped with an automatic time correction, which in turn is made possible with the aid of the satellite signals.

If the navigation processor determines that the basic location finding is less accurate than the GPS location finding, the currently calculated position is corrected using the GPS data.

In addition to this the sequence of locations calculated by the GPS is used to determine the vehicle's route.

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

Possible interference when receiving GPS signals

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

Atmospheric interference e.g. weather, water vapor, fog
Multipath reception due to reflection of the signals e.g. from walls of buildings
Signal shading e.g. in built-up areas, in tunnels, by high buildings, by trees

GPS reception therefore necessitates a clear view of the sky. Positioning accuracy lies at approx. 10 m.

Map-based position finding, function

GF82.61-P-3008TJ