Global navigation satellite systems

GPS (and its Russian analogue, GLONASS) are reviewed. Conceived a quarter of a century ago, it represents the most significant step forward in radionavigation. Its deployment was relatively slow. The explosive growth of low cost civil receivers has only appeared in the last five years or so, and the relationship between the US military authorities, who own and operate GPS, and the civil international community, is slow in developing a mutually acceptable position. A review of GPS against the required navigation performance criteria leads to the requirements for augmenting GPS into GNSS-1-in particular WAAS by the FAA, EGNOS by the European tripartite group, and MSAS in Japan. A description of these augmentation systems, based on navigation payloads on board geostationary satellites, is given, with particular reference to Inmarsat. Associated institutional issues are discussed briefly as well as an interactive synthesis of candidate designs for GNSS-2.