6.3 Options for improving accuracy in coordinate measurements
The most important performance measure of GPS units for most users is accuracy. There are many systems to improve the accuracy of positioning information provided by the GPS. Enhancement methods of improving accuracy rely on external information being integrated into the calculation process.
Examples of augmentation systems:
Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations. DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. The digital correction signal is typically broadcast locally over ground-based transmitters of shorter range. There are many operational systems in use throughout the world, around 47 countries operate DGPS systems. A list can be found at World DGPS Database for DxersOmniSTAR is a satellite based augmentation system (SBAS) service provider. OmniSTAR correction signals are proprietary, and a subscription must be bought from the OmniSTAR corporation to receive a subscription authorization. OmniSTAR uses geostationary satellites in 8 regions covering most of the landmass of each inhabited continent on Earth. To access the OmniSTAR solution the user must have an OmniSTAR capable receiver. OmniSTAR HP corrections are modeled on a worldwide network of reference sites using carrier phase measurement to maximize accuracy. The expected 2-sigma (95%) accuracy of OmniSTAR HP is 10cm. It operates in real time and without the need for local Base Stations or telemetry links.