Broadcast versus precise ephemerides: a multi-GNSS perspective

Abstract

A consistent analysis of signal-in-space ranging errors (SISREs) is presented for all current satellite navigation systems, considering both global average values and worst-user-location statistics. The analysis is based on 1 year of broadcast ephemeris messages of the Global Positioning System (GPS), GLONASS, Galileo, BeiDou and QZSS collected with a near-global receiver network. Position and clock values derived from the navigation data are compared against precise orbit and clock products provided by the International GNSS Service and its multi-GNSS experiment. Satellite laser ranging measurements are used for a complementary and independent assessment of the orbit-only SISRE contribution. The need for proper consideration of antenna offsets is highlighted and block-/constellation-specific radial antenna offset values for the center-of-mass correction of broadcast orbits are derived. Likewise, the need for application of differential code biases in the comparison of broadcast and precise clock products is emphasized. For GPS, the analysis of the legacy navigation message is complemented by a discussion of the CNAV message performance based on the first CNAV test campaign in June 2013. Global average SISRE values for the individual constellations amount to 0.7 ± 0.02 m (GPS), 1.5 ± 0.1 m (BeiDou), 1.6 ± 0.3 m (Galileo), 1.9 ± 0.1 m (GLONASS), and 0.6 ± 0.2 m (QZSS) over a 12-month period in 2013/2014.