DGPS is an improvement of standard GPS technology. The acronym stands for 'Differential Global Positioning Technology'

This term describes a method which corrects several GPS miscalculations. The result is an accuracy of 1 to 3 meters compared with 5 to 12 meters of the standard GPS.

DGPS works as follows:
The calculation of a position is the result of the cooperation between two receivers, not one (as with GPS). One of these receivers is roving (e.g., in the vehicle), while the other one, called 'reference receiver', is mounted at a fixed reference point.

The location of the reference receiver must once be measured very accurate. Given the fundamentals of satellite technology, even if the reference receiver is a few hundred kilometres away from the roving receiver, the timing of the GPS satellite signals will virtuallyhave the same errors.
Thus, using its known position, the reference receiver calculates the timing errors of the GPS satellites and relays them to the roving receiver. This 'differential' process allows for very precise calculation of the position of the roving receiver.