SBAS General Introduction

Fundamentals
Title	SBAS General Introduction
Author(s)	GMV
Level	Basic
Year of Publication	2011

A Satellite-based Augmentation System (SBAS) is a civil aviation safety-critical system that supports wide-area or regional augmentation – even continental scale - through the use of geostationary (GEO) satellites which broadcast the augmentation information. A SBAS augments primary GNSS constellation(s) by providing GEO ranging, integrity and correction information. While the main goal of SBAS is to provide integrity assurance, it also increases the accuracy with position errors below 1 metre (1 sigma).

Introduction

As defined by the International Civil Aviation Organization (ICAO), a Global Navigation Satellite System (GNSS) is a worldwide position and time determination system that includes one or more satellite constellations, aircraft receivers, and system integrity monitoring, augmented as necessary to support the required navigation performance for the intended operation. Current satellite navigation systems (GPS, GLONASS) were not designed to meet the real-time integrity monitoring capability required by the civil aviation navigation safety needs. To overcome the above limitation, several Augmentation Systems have been put in place. A Satellite Based Augmentation System (SBAS) is a wide-area differential augmentation system. A network of ground stations at known positions is deployed over the SBAS service area in order to monitor the ranging signals of the satellite constellation. The SBAS collects and process all the input data provided by the station network in order to compute (see SBAS Fundamental for further details) and provide corrections to the original navigation information of the primary constellation (satellite orbit and clock errors, ionospheric errors) and its integrity bounds information over a certain region. The SBAS navigation message is disseminated over the service area by a GEO. Currently, several SBAS systems are in an operational capability, WAAS in United States, EGNOS in Europe, and MSAS in Japan, or under development, SDCM in Russia Federation or GAGAN in India). Finally, it is worth noting that both the service providers (operational SBAS system point of view) and the SoL service users (SBAS receivers) shall be developed and operated being compliant with international recognized standards (see SBAS standards) in order to assure a high degree of interoperability between different SBAS.

The following sections include further information about different important topics related to a SBAS. SBAS Fundamentals introduces the main general architecture of a SBAS, including what are the main architectural elements, its design challenges, and the functionaillites and objectives of each component. The SBAS Standards section summarizes the international bodies in charge of the standardization of SBAS systems, the principle applicable documents and its current status. Finally, SBAS Systems sections provides a brief overview of the current existing SBAS as well those which are in development process.