Regional Systems

Abstract

Satellite-based augmentation systems (SBASs) are designed to enhance the performance of standard global navigation satellite system (GNSS) positioning. SBASs improve the positioning accuracy by providing corrections for the largest error sources. More importantly, SBASs provide assured confidence bounds on these corrections that allows users to place integrity limits on their position errors. Several systems have been implemented around the world and several more are in development. They have been put into place by civil aviation authorities for the express purpose of enhancing air navigation services. However, SBAS services have been widely adopted by other user communities, as the signals are free of charge and easily integrated into GNSS receivers. This chapter describes the basic architecture, functions, and application of SBAS. Because the key motivation behind SBAS is integrity, it is essential first to understand the error sources that affect GNSS and how they may vary with time or location. It is then explained how the corrections and confidence intervals are determined and applied by the user. The different SBASs that have been developed around the world are described and how they are developed to the same international standards such that each is interoperable with the others. The performances and services of each system are described. Finally, the evolution of SBAS from its current single-frequency single-constellation form into systems that support multiple-frequencies and multiple-constellations is described. The goal of this chapter is to explain the motivation for developing SBASs and provide the reader with a working knowledge of how they function and how they may be used to enhance GNSS positioning accuracy and integrity.