SBAS
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Contents
Overview
Global Navigation Satellite System (GNSS) performance can be improved by regional Satellite-based Augmentation Systems (SBASs). 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.
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.
The European Space Agency, in cooperation with the European Commission (EC) and EUROCONTROL (European Organization for the Safety of Air Navigation) has developed the European Geostationary Navigation Overlay Service (EGNOS), an augmentation system that improves the accuracy of positions derived from GPS signals and alerts users about the reliability of the GPS signals.
Three EGNOS satellites cover European Union member nations and several other countries in Europe. EGNOS transmits differential correction data for public use and has been certified for safety-of-life applications. EGNOS satellites have also been placed over the eastern Atlantic Ocean, the Indian Ocean, and the African mid-continent.
Wide Area Augmentation System (WAAS)
The US Federal Aviation Administration (FAA) has developed the Wide Area Augmentation System (WAAS) to provide GPS corrections and a certified level of integrity to the aviation industry, to enable aircraft to conduct precision approaches to airports. The corrections are also available free of charge to civilian users in North America.
A Wide Area Master Station (WMS) receives GPS data from Wide Area Reference Stations (WRS) located throughout the United States. The WMS calculates differential corrections then uplinks these to two WAAS geostationary satellites for broadcast across the United States.
Separate corrections are calculated for ionospheric delay, satellite timing, and satellite orbits, which allows error corrections to be processed separately, if appropriate, by the user application.
WAAS broadcasts correction data on the same frequency as GPS, which allows for the use of the same receiver and antenna equipment as that used for GPS. To receive correction data, user equipment must have line of sight to one of the WAAS satellites.
Multi-functional Satellite Augmentation System (MSAS)
MSAS is an SBAS that provides augmentation services to Japan. It uses two Multi-functional Transport Satellites (MTSAT) and a network of ground stations to augment GPS signals in Japan.
GAGAN is an SBAS that supports flight navigation over Indian airspace. The system is based on three geostationary satellites, 15 reference stations installed throughout India, three uplink stations and two control centers. GAGAN is compatible with other SBAS systems, such as WAAS, EGNOS and MSAS.
System for Differential Corrections and Monitoring (SDCM)
The Russian Federation is developing SDCM to provide Russia with accuracy improvements and integrity monitoring for both the GLONASS and GPS navigation systems. By 2016, the Russian Federation plans to provide L1 SBAS coverage for all Russian territory and by 2018 L1/L5 coverage. SDCM will also provide Precise Point Positioning (PPP) services for L1/L3 GLONASS by 2018.
Other systems
- China: Satellite Navigation Augmentation System (SNAS) (in development)
- South Korea: Wide Area Differential Global Positioning System (WADGPS) (in development)
