## 3 Results and Discussion
We can conclude that the SICB variations should be very small for the BDS-3S satellites. According to [PERSON] et al. [20], the results using a 40-m dish antenna to remove ground multipath effects revealed that the SICB variations still existed in the code observations of the three new navigation signals and two legacy signals of all four BDS-3S satellites, although they were confined to a peak amplitude of about 0.1 m. In addition, the elevation-dependent variations of SICB were still noticeable in the legacy bands of B1 and B3 for the BDS-3S IGSO satellites. As to the SICB values for the signals of BDS-3S MEO satellites on B1 and B3 frequencies and for all new navigation signals, they have a certain relationship with both azimuths and elevations. Thus, an effective elevation-dependent SICB correction model on the legacy B1 and B3 frequencies for BDS-3S IGSO satellites should be established. Moreover, we still establish the elevation-dependent SICB correction model for the signals of BDS-3S MEO satellites on B1 and B3 frequencies to further confirm the conclusions given in [PERSON] et al. [20]. The CMN can be used as an important index to characterize the quality of code observations. Figure 9 shows the dependence of RMSs of the high-frequency components in the time series of MP combinations on the satellite elevations at station SGG1. The RMSs are calculated for each increment of 5\({}^{\circ}\) in satellite elevations. It is clearly seen that B3, B2a and B2b exhibit the smallest CMN (Figure 9), which are signals with a high chipping rate of 10.23 Mcps. The chipping rates of all BDS signals are provided in [PERSON] et al. [22]. The B2a, B2b and B3 signals of BDS-3S satellites show a comparable performance for CMN, and the RMS CMN is 15-23 cm at low elevation angles and 2-3 cm at zenith. As to the B1C signal of BDS-3S satellites, pseudorange errors of 13 cm are obtained close to zenith (90\({}^{\circ}\)), whereas increased values of about 0.6 m are encountered at low elevations. The RMS CMN of BIC signal is systematically larger than that of B1 signal by several centimeters because of the lower code chipping rate of B1C, which is equal to half that of B1 signal. The unexpected RMS statistics of CMN for B1 signal at satellite elevation angles from 30\({}^{\circ}\) to 50\({}^{\circ}\) can be attributed to the scarce observations. Compared with the BDS-3S satellites, the BDS-2 CMN on B1 and B3 frequencies show superior performance at mid and low elevations, and exceeds the BDS-3S CMN by several millimeters to 2 cm at elevation angles higher than 60\({}^{\circ}\). The CMN for the BDS-2 B2 signal is of the same order of magnitude as that for the BDS-2 B1 signal. Differing surroundings near the station and the differing tracking performance of specific receivers and antennae in terms of multipath sensitivity will cause CMN differences, which can be revealed by direct comparison with the results from XIA1 of 2-15 September 2016 shown in the bottom sub-panels of Figure 9. The CMN results for B2a frequency at station XIA1 have to be excluded because of frequent gross errors. Based on the MP combination time series from all the selected days and stations, the elevation-dependent piecewise linear correction model parameters for SICB with an elevation node separation of 1\({}^{\circ}\) are estimated for each frequency covered by this study, and for each BDS-3S and BDS-2 satellite. With the use of linear interpolation, we can obtain the SICB corrections between given nodes. We should add the corrections to the original code observations so that the SICB variations can be removed. The estimated correction model parameters for BDS-2 satellites are shown in Figure 10. The code observations in the B1 band from BDS-2 MEO satellites are seriously impacted by SICB, and the SICB corrections reach approximately 0.9 m close to zenith. The SICB variations have much less effect on the BDS-2 IGSO satellites than the BDS-2 MEO satellites. The code observations on the B2 frequency are less affected by the SICB than those on the B1 frequency.