## 3 Results and Discussion
After applying the SICB corrections derived from the traditional SICB correction model to the original code observations, the MP combinations are re-formed, and their distributions for the BDS-2 IGSO and MEO satellites are illustrated in Figure 8.6 The RMSs of the MP series are also computed and provided in each panel, and are 0.422, 0.364 and 0.400 m, and 0.448, 0.355 and 0.364 m for BDS-2 IGSO and MEO satellites on the B1, B2 and B3 frequencies, respectively. In conjunction with the results shown in Figures 12 and 13, the above RMS statistics are smaller than those of uncorrected MP series, but slightly larger than those of corrected MP series with the improved SICB correction model proposed here, indicating that our improved SICB correction model outperforms the traditional SICB correction model. Since the traditional SICB correction model cannot retrieve the effective elevation-dependent code biases for the BDS-3S satellites, the analysis of SICB mitigating for these satellites is confined to the improved SICB correction model. Figure 17 provides the distribution of MP combination time series without and with SICB corrections on B1 and B3 frequencies for BDS-3S IGSO satellites C31 and C32. Both uncorrected and corrected MP combinations are close to a normal distribution, but the latter ones account for a larger percent of smaller errors. The RMS statistics of the MP time series are calculated and displayed in each panel. About 0.32 and 0.35 million epoch-wise MP values are involved in the calculation of RMS values for C31 and C32, respectively. The decrease of the corrected MP series on the RMS values is 4% and 3% compared to the uncorrected MP series of the B1 and B3 frequencies for C31, respectively, while the corresponding decreases for C32 are 3% and 1% for the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Item** & **Traditional SICB Correction** & **Improved SICB** & **Superiority of** \\  & **Model** & **Correction Model** & **Improved Model** \\ \hline Integer phase & Estimated as average values of & Eliminated by & Free of effects of MP \\ ambiguities and constant & MP series over each continuous & between-elevation single & combination \\ hardware delays & ambiguity block & difference & inconsistency \\ \hline Elevation node & & & More precise \\ separation & \(5^{\circ}\) & \(1^{\circ}\) & elevation-dependent \\  & & & SICB variations \\ \hline Estimation approach & Least-squares adjustment & Average processing & Easier implementation \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparisons of the traditional and improved SICB correction models. Figure 15: Traditional SICB correction model as a function of elevations on B1, B2 and B3 frequencies for each BDS-2 MEO and IGSO satellite. two frequencies, respectively. The reason for the small improvement is that the SICB variations on the two frequencies are at a level of only several centimeters for BDS-3S IGSO satellites. However, such a centimeter-level range of variance for SICB cannot be neglected for precise positioning applications in which code observations play a very important role. Benefiting from the consideration of MP combination consistency and the denser elevation node separation, the effective SICB correction model for the B1 and B3 signals of BDS-3S IGSO satellites is successfully established. Figure 18 shows the distribution of uncorrected and corrected MP combination time series of B1 and B3 frequencies for BDS-3S MEO satellites C33 and C34. Both uncorrected and corrected MP combinations are approximately normally distributed. Moreover, the distribution is nearly identical for the two different groups of MP combinations. In each panel, the RMSs of MP series are also presented. Unlike the results shown in Figures 12, 13 and 17, the RMS values of MP time series of BDS-3S MEO satellites are slightly increased by 1-6 mm after applying the SICB corrections. This is because the SICB variations on B1 and B3 frequencies are related not only to the elevation angles, but also to the azimuth angles of BDS-3S MEO satellites [20].