## 5 Results and Discussion
### Elevation-Dependent Code Bias Analysis  
The MP combination value of the BDS-2 satellite has a strong correlation with the satellite elevation in earlier findings [2]. It can be seen from Figure 3 that the MP combination values of the BDS-3 satellites vary with elevation. The overall trend of the MP combination time series of the C20 and C23 satellites varies monotonously with elevation, except for the MP combination time series of C20 with elevations below 30\({}^{\circ}\). Other satellites have the highest elevations in the observed arc segment, but the MP combination values of the same elevation are not exactly equal, as is shown in Figure 3. In order to further explore the relationship between the MP combination values and elevations of the BDS-3 satellites, Figure 5 shows the MP combination time series with respect to elevation. There is obvious elevation-dependent code bias variation for the C28 B1I/B2b/B3I/B1C/B2a frequency bands, compared with those present for other satellites. Similarly, the MP combination of B3I has an obvious elevation-dependent variation in a range of 0.1 m for C19/C21/C24/C27/C28/C37. The obvious elevation-dependent variation of the B2a and B2b frequency bands also exists in most satellites with a range of 0.1 m, but the MP combination values of some satellites are asymmetric with respect to elevation, which is especially obvious for the B1I and BIC frequency bands with elevation-dependent variations of 0.2 m, which indicates that the code bias variation is not uniquely related to elevation, especially for the B1I/BIC frequency bands. This performance also appears in the B1C frequency band for three BDS-3 experimental satellites [15]. The code bias variation may have a certain relationship with elevations and azimuths, which deserves further study with more observations. The code bias variations that are asymmetric with respect to elevation can be considered the satellite-induced code bias variations, since the code bias variations differ from different satellites. What's more, the satellite-induced code bias variation of the BDS-3 satellites in a range of 0.1-0.2 m is greatly reduced compared with that of the BDS-2 satellites [2; 7]. In order to explore the regularity of the same frequency and elevation on different satellites, the RMS values are calculated for every elevation range of 5\({}^{\circ}\) for the MP combination values of all frequency bands of monotonic changes in elevations from 10\({}^{\circ}\)-90\({}^{\circ}\), which can be seen in Figure 6. As is shown in Figures 5 and 6, the MP combination time series is the most unstable at elevations below 30\({}^{\circ}\), which is most vulnerable to interference from MP errors. This can be considered in the stochastic model of GNSS data processing; however, not all the RMS values and MP combination values decrease with increased elevation all the time. The RMS value of the B1I/B1C frequency bands increases at elevations of 40\({}^{\circ}\)-70\({}^{\circ}\); the RMS value of the B2a frequency band increases at elevations of 60\({}^{\circ}\)-90\({}^{\circ}\). The BDS-3 satellites are manufactured by two manufacturers, the Shanghai Engineering Center for Microsatellites (SECM) of the China Academy of Science (CAS) and China Academy of Space Technology (CAST) [28]; the RMS values of the MP combination values are shown for both manufacturers in Figure 7. The C19/C21/C22/C23/C24/C32/C33/C37 satellites manufactured by CAST and C25/C26/C27/C28/C30/C35 satellites manufactured by SECM are used to analysis the trends. The code bias of the two manufacturers is different for elevations below 25\({}^{\circ}\), but the difference decreases with the increase in elevation, which indicates that the satellite-induced code variations of the two manufacturers have no obvious difference at elevations greater than 25\({}^{\circ}\). Figure 5: The MP combination time series tracked by a 40 m dish antenna with respect to elevation for each BDS-3 satellite frequency band observed.