GNSS orbit ephemeris is broadcast to users for computing the position of a navigation satellite. The orbit ephemeris is estimated by the ground facility, which is the operational control segment (OCS) of the GPS, and affects the accuracy of the user’s navigation solution (Hofmann-Wellenhof et al. 2008). Currently, estimated performance tends to improve when using the differential GNSS (DGNSS) implementation, so ramifications of ephemeris error to the user are very small in limiting cases. However, the integrity issue has been magnified recently along with user accuracy requirements. In particular, integrity can determine system availability and any other requirements faced within the aviation community (Pervan & Chan 2003). Ephemeris constitutes a threat to integrity of the GNSS, in this regard, we propose an ephemeris protection level based on long baseline references condition.

Keywords: GNSS, ephemeris, protection level, long-baseline reference stations