GNSS (Global Navigation Satellite System) provides some information (ephemeris, satellites clock correction, satellites status..) for user using navigation message. Ephemeris is information for calculating satellite position and is one of factors of position performance (accuracy). In the aviation society, navigation system has to guarantee the integrity requirement as well as accuracy. There are lots of fault detection algorithms against threat factors. We consider the ephemeris fault detection algorithm, which uses the baseline vectors between reference station antennas. This algorithm estimates length of baseline vector using law of cosine, and then compare with true length of baseline vector. In this paper, we figure out relation between ephemeris fault (satellite position) and test statistics, with equation derived and real GPS reference station data. These results contribute eployment of reference stations which use ephemeris fault detection algorithm based on baseline vector information.

Keywords: GNSS, ephemeris, fault detection, baseline length estimation