transmits correction signals to GPS navigation equipment on board. It provides an improved location accuracy integrity, in the range of operations of each system, from the 15 meter nominal gps accuracy to about  1-3cm in case of the best implementations. This technique was developed in the early 1980’s, and it is widely used in various forms. Each DGPS uses a network of fixed ground-based reference stations to broadcast the difference between the positions indicated by the GPS satellite system and known fixed positions. These stations broadcast the difference between the measured satellite pseudo ranges and actual pseudo rangers, and receiver stations may correct their pseudo ranges, by the same amount. The digital correction signal is typically broadcasted locally over ground-based transmitters of shorter range.
