A Comparative Study of SBAS Systems for Navigation in Geostationary Orbit

Kurzfassung

Real data has been collected from space demonstrating the CanX-2 receiver’s ability to track the WAAS, EGNOS, GAGAN, and MSAS systems. Two types of analysis were performed, in order to assess the suitability of SBAS ranging measurements as a source of positioning information for users in geostationary and other higher orbits, in which SBAS satellites may be permanently in view while GPS visibility is severely limited by the shape of the transmit gain patterns. The first analysis, of the transmit gain patterns of the EGNOS, WAAS, MSAS and GAGAN systems, revealed that all the SBAS satellites transmit enough power to be tracked over the earth’s limb. It was revealed that GAGAN has a narrow gain pattern than the other SBAS systems, WAAS and EGNOS appear to have similar gain patterns but WAAS has a higher transmit power by 2-4 dB, and MSAS appears to transmit lower signal power than the other systems but uses an antenna design providing more even global coverage, which results in and stronger power transmitted towards the edge of the earth. The second study determined that the SBAS ranging capability was useable in space, provided that the fast correction data transmitted by the SBAS satellites was applied in addition to the MT9 broadcast ephemeris. The SBAS ranging accuracy is lower than it is for the standard GPS MEO signals, but in most cases the errors are within +/- 10 m for WAAS and +/- 20 m for MSAS and GAGAN. EGNOS does not support ranging. Provided the lower accuracy compared to GPS is taken into account, the SBAS systems could be used to provide positioning and timing information to users in GEO or other orbits above the MEO GNSS constellations