Determination of the Differential Code Bias for Current BDS Satellites

The differential code bias (DCB) in global navigation satellite system (GNSS) satellites should be precisely determined using real ground GNSS data when designing certain applications, such as ionospheric remote sensing, precise positioning, and timing. Different from GPS with a full constellation, the number of BDS (BeiDou Satellite System developed by China) satellites currently in orbit is very limited, and the data from BDS are insufficient for estimating satellite DCB simultaneously with ionospheric total-electron-content modeling. In view of this, a calibration approach, namely, GPS-aided DCB determination (GPSADCB), is proposed to estimate the DCB of current BDS satellites with the aid of GPS data. The data from GPS are used to derive the ionospheric delay along the propagation path of the BDS signal. Before applying GPSADCB to estimate the DCB of current BDS satellites, the performance of this approach is first validated using two sets of GPS data in a simulated BDS case. Then, a continuous four-day data set gathered by two BDS receivers is used to determine the DCB of current BDS satellites based on GPSADCB. Validation results indicate that the difference of DCB estimates between GPSADCB and the Center for Orbit Determination in Europe is about 0.3 ns and the stability of DCB estimates in one month is about 0.2 ns. The DCB of different BDS satellites ranges from -10 ns to 13 ns, and the mean of day-to-day scatter for DCB estimates is below 0.2 ns over the period of data collection. It is demonstrated that the proposed approach can be used to estimate BDS satellite DCB at the initial stage with a few satellites in orbit.