Development of the EGNOS Pseudolite System

In order to access the Satellite Based Augmentation System (SBAS) service, the end user needs to have a direct line of sight to at least one of the Geostationary Earth Orbit (GEO) satellites transmitting the augmentation messages. This requirement is critical for users in environments such as city canyons, valleys and fjords since high buildings and mountains in the vicinity of the end user can easily block the lines of sight to the GEO satellites. The situation becomes worse at high latitudes because of the low elevation angles to the GEO satellites. Even a very low obstacle can block the lines of sight to the GEO satellites. This limitation reduces SBAS Signal in Space (SIS) availability significantly at high latitude especially for land applications. This paper presents a solution of transmitting the European Geostationary Navigation Overlay Service (EGNOS) SIS using a pseudolite. The EGNOS pseudolite functions in a similar way as a GEO satellite. It will provide not only a terrestrial-based solution for transmitting the EGNOS SIS, but also a ranging measurement for the navigation solution. The EGNOS pseudolite system mainly consists of a Master Control Station, an EGNOS Data Server, EGNOS pseudolites and the user terminal. A preliminary test on a surveyed site has been carried out to verify the functionalities of the system. The data set collected from the test has been processed with two scenarios: one with four GPS satellites, while the other with three GPS satellites plus an EGNOS pseudolite. Both data processing scenarios have similar satellite geometries. The test result shows that the positioning accuracies are similar for both scenarios.