Autonomous satellite state determination by use of two-directional links

The European Commission recently announced the development of a new satelli te navigation system called 'Galileo'. It shall be a system compatible with GPS but shall have an improved performance compared to existing systems, R esults of a study under a contract of the European Space Agency (ESA) with respect to achievable improvements of ephemeris and clock state determinati on as well as of integrity by use of intersatellite links and board-autonom ous measurements to ground reference stations are presented. Simulation and analyses for two different aspects were performed. The first aspect was th e determination of the satellite state using intersatellite links and a con ventional ground network, In the second aspect, additional two-way ground-r eferenced links were added and the performance analysis was repeated for su ch a configuration with emphasis on autonomous measurements on board the sa tellites. The simulations were performed for a global GEO/IGSO and a global GEO/LEO satellite constellation, but we expect that the main results are s imilarly applicable to the GEO/MEO or MEO constellation, which is suggested to be used with Galileo, With respect to the integrity performance, the ME O constellation was analysed separately. Copyright (C) 2000 John Wiley & So ns, Ltd.