This paper characterizes the GLONASS broadcast clock and ephemeris performance over an eight year period from 2009 through 2016, where both nominal signal-in-space (SIS) user range error (URE) and faulty behavior are explored. While GPS is currently widely used in aviation via receiver autonomous integrity monitoring (RAIM), advanced RAIM (ARAIM) could allow for a multi-GNSS navigation solution that potentially includes GLONASS. In order to demonstrate the safety of such a system, the performance of each GNSS must be carefully evaluated. GLONASS broadcast clock and ephemeris parameters are evaluated through comparison with precise clock and ephemeris products provided by the International GNSS Service (IGS). Clock and ephemeris error are combined to produce SIS URE values and compared against fault criteria. More than 300 faults over the last eight years have been identified and categorized by whether they are faults in clock and/or ephemeris, the health state of the satellite preceding the fault event, the duration of the fault, and other criteria. The data shows a significant improvement in fault rate and duration, where several classes of faults that were once relatively common have not been observed in several years. Additionally, due to limited GLONASS monitoring and upload stations, a geographic correlation with fault events is observed. This paper estimates the probability of independent satellite faults, P-sat, and probability of simultaneous satellite failures, P-const, over this period. Nominal SIS URE performance is also examined, where SIS ranging biases and error distributions are assessed for each satellite for both clock and ephemeris. The analysis shows nominal ranging accuracy improvement since 2009 in both clock and ephemeris.
