The performance of Global Navigation Satellite Systems (GNSSs) can be improved by regional Satellite-based Augmentation Systems (SBASs), 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.
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).
All of these systems comply with a common global standard and are therefore:
- Compatible: they do not interfere with each other;
- Interoperable: a user with a standard receiver can benefit from the same level of service and performance, regardless of what coverage area they are located in.
SBAS in use
SBAS is essential for applications where accuracy and integrity are critical. In particular, SBAS is indispensable in situations where people’s lives are at stake or where a form of legal or commercial guarantee is required and GNSS is being used. For example, in the aviation sector GPS does not satisfy the strict operational requirements set by the International Civil Aviation Organisation (ICAO) for use in such critical flight stages as final approaches. However, with the addition of SBAS, ICAO standards are satisfied.
Beyond the aviation sector, SBAS improves and extends the scope of such GNSS applications as precision farming, on-road vehicle fleet management and geodesy – to name only a few.