Differential GPS (DGPS) utilizes two GPS receivers, one stationary (base station) and one mobile (rover), both tracking the same GPS signals. The base station, used as a reference point, determines what errors the satellite data contains and this data is used to correct the data received by the mobile receivers. The correction can either be applied in real-time or processed later by downloading the correction files from the base station receiver; this is called post-processing. The main reason behind all this is to eliminate some of the errors like multipath that the mobile unit might receive.

Another form of DGPS which is both ground based and satellite based is WAAS.