The performance of Global Navigation Satellite Systems (GNSSs) can be improved by regional Satellite-based Augmentation Systems (SBAS), such as the European Geostationary Navigation Overlay Service (EGNOS).
SBAS improves the accuracy and reliability of GNSS information by correcting signal measurement errors and by providing information about the accuracy, integrity, continuity and availability of its signals.

SBAS uses GNSS measurements taken by accurately located reference stations deployed across an entire continent.
All measured GNSS errors are transferred to a central computing centre, where differential corrections and integrity messages are calculated.
These calculations are then broadcast over the covered area using geostationary satellites that serve as an augmentation, or overlay, to the original GNSS message.

Existing SBAS

Several countries have implemented their own Satellite-based Augmentation System.
For example, in Europe EGNOS covers the majority of the European Union (EU), along with some neighbouring countries and regions. Other national SBASs include:

• USA: Wide Area Augmentation System (WAAS)

• Japan: Multi-functional Satellite Augmentation System (MSAS)

• India: GPS and GEO Augmented Navigation (GAGAN)

• China: Satellite Navigation Augmentation System (SNAS) (in development)

• South Korea: Wide Area Differential Global Positioning System (WADGPS) (in development)

• Russia: System for Differential Corrections and Monitoring (SDCM) (in development).