Integration of a SBAS-Based Positioning Architecture into a Satellite Digital Radio Broadcasting (S-DB) LBS Platform

As "Road/mobility" services based on a GNSS position are emerging, specific limitations of the GPS drives the need for innovative system architectures. Toll collection, enhanced turn-by-turn navigation or fleet management, all suffers from the degradation of accuracy in urban context and the lack of integrity of the resulting navigation solution. The need for improved performances (as compared to GPS stand-alone), with high level of integrity has pushed International Organization for Civil Aviation to recommend and standardize the specifications for the GPS augmentations SBAS "Satellite Based Augmentation Systems". In Europe, the civil aviation authorities and the European Space Agency have developed EGNOS, which is the European SBAS (like WAAS is the American SBAS) in order to provide to the existing and forthcoming GNSS an increased accuracy, and an integrity signal. But a challenging reception environment for GPS receivers, such as urban areas, could also take great advantage of the benefit of EGNOS. Studies have been conducted by the ESA concluding that EGNOS does not only improve accuracy of positioning, it also increases the availability of a given level of accuracy over urban areas. For instance, in an environment where a plain GPS receiver has a probability of 50% to obtain a 40m accuracy, a GPS+EGNOS receiver reaches the same accuracy with a probability of over 99%, and has a probability of 60% to obtain accuracy better than 5m. (ref [1]). Unfortunately, most urban contexts in Europe will deprive a road user from the EGNOS signal because of the relatively low elevation of a geostationary satellite (typically, around 30° for a 45°N European site). The RELY project is a smart alternative solution to allow the use of the EGNOS signal through a hybrid source of downlink. RELY is a European Commission IST project which aims at demonstrating the provision of multicast services to in-vehicle mobile terminals using a hybrid satellite-terrestrial broadcasting system on a European dimension. The project started in April 2002 and has duration of 2 years. The Satellite Digital Radio Broadcasting (S-DB) system implemented in RELY is based on a hybrid technology composed of a GEO satellite and terrestrial repeaters. The satellite enables to efficiently cover large regions (country or pan-European size), whereas the terrestrial repeaters ensure the coverage continuity in urban areas. The main innovation in RELY is to couple an hybrid digital radio broadcast system with a standard positioning system (such as GPS) and the EGNOS signal, to provide a high quality/low cost onboard positioning solution. In the RELY project, EGNOS signal is also available via S-DB. This diversity of channels (S-DB and INMARSAT) ensures a very good availability of the EGNOS data, hence bridging continuity holes in urban areas. This paper describes the overall RELY architecture, focusing on the navigation aspect of the project, and presents first assessments of factory trials.