Effect of Tracking Stations Distribution on the Estimation of Differential Code Biases by GPS Satellites Based on Uncombined Precise Point Positioning

Ionospheric observations including the slant total electron content (STEC) and satellite-receiver's differential code bias(DCB) can be extracted precisely by an uncombined precise point positioning(PPP) technique. Moreover, a GPS satellite DCB can be determined using the “IGGDCB” approach at high accuracy. A new strategy for combining uncombined PPP and “IGGDCB” is proposed in this paper to investigate the effect of distribution of tracking stations on the estimation of DCB in GPS satellites. Consecutive 15-day data from different numbers of IGS stations in Europe and globally during a high solar activity period were chosen for this study. In order to assess the precision of satellite DCB estimates in this experiment, CODE monthly satellite DCB estimates were considered as the true value. Our experimental results show that satellite DCB can be calibrated precisely by the proposed method. The RMS of the difference between DCB estimates and corresponding CODE value is less than 0.2 ns based on the data from Europe, while it is less than 0.1ns based on the global data. These results were better than the results from the smoothed code data. In addition, the day-to-day variation can be reduced with the increase of contributed stations, whilst the RMS and day-to-day variation of daily satellite DCB estimates can be both reduced based on the global data.