## 3 Results
### Impact of CNCORS on BDS Single-System POD
#### 3.2.1 Overlapping Arcs Precision  
Table 8 and Figure 3 show that the overlapping arcs precision from Strategy 3,which is based on the CNCORS and MGEX stations, has 3 DRMS of 19.0, 7.6, and 11.0 cm for the GEO, IGSO, and MEO  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Strategies** & **PRN** & **CO1** & **CO2** & **CO3** & **CO4** & **CO5** & **CO6** & **CO7** & **CO8** & **CO9** & **C10** & **C15** & **C11** & **C12** & **C14** \\ \hline S1/S3 & 51.5 & 44.7 & 38.4 & 53.7 & 45.2 & 38.0 & 37.8 & 39.5 & 40.2 & 40.6 & 42.1 & 25.2 & 26.8 & 28.1 \\ S2/S4 & 65.2 & 51.3 & 44.8 & 60.0 & 51.3 & 45.0 & 44.9 & 46.4 & 46.4 & 47.2 & 48.6 & 26.9 & 28.1 & 29.8 \\ \hline \hline \end{tabular}
\end{table}
Table 7: ODOP comparison of different strategies.  
satellites, respectively. Among them, IGSO satellites have the highest precision, because more stations exist within the operation area of IGSO satellites, with stations in China, Southeast Asia, Australia, and the surrounding areas. These ground stations are evenly distributed in this region and able to provide a longer observation period for IGSO satellites. Compared with strategy 4, the average 3D precision of the GEO, IGSO, and MEO satellites of strategy 3 is improved by 15.6%, 29.6%, and 5.2%, respectively. IGSO satellites experience the most improvement, which is consistent with the results of the joint orbit determination in the previous section.  
For Strategy 3, the average radial RMS of all three types of satellites is better than 3.5 cm, and the cross-track RMS is better than 4.5 cm. For the along-track direction, the RMS is 4.6 cm for IGSO satellites, 18.1 cm for GEO satellites, and 9.4 cm for MEO satellites. Therefore, the orbit precision from the BDS single-system method can be relatively high in cases with more evenly distributed ground tracking stations. GEO satellites have the worst accuracy in the along-track direction because their stationary characteristics are related to large orbit errors, and the along-track orbit component of GEO satellites is strongly correlated with other parameters, such as ambiguities.  
Figure 3: _Cont._  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Satellite Type**} & \multicolumn{2}{c}{**Along-Track**} & \multicolumn{2}{c}{**Cross-Track**} & \multicolumn{2}{c}{**Radial**} & \multicolumn{2}{c}{**3D**} \\ \cline{3-10}  & **PRN** & **S3** & **S4** & **S3** & **S4** & **S3** & **S4** & **S3** & **S4** \\ \hline \multirow{5}{*}{GEO} & C01 & 20.5 & 24.8 & 2.7 & 3.3 & 2.8 & 3.5 & 21.2 & 25.3 \\  & C02 & 18.7 & 18.9 & 2.7 & 3.3 & 3.1 & 4.2 & 19.1 & 19.7 \\  & C03 & 14.5 & 20.4 & 2.7 & 3.5 & 2.1 & 2.5 & 15.1 & 21.3 \\  & C04 & 19.0 & 19.5 & 3.5 & 4.9 & 4.1 & 4.8 & 20.0 & 21.1 \\  & C05 & 17.9 & 24.0 & 4.5 & 5.1 & 4.0 & 4.5 & 19.6 & 25.2 \\  & **mean** & **18.1** & **21.5** & **3.2** & **4.0** & **3.2** & **3.9** & **19.0** & **22.5** \\ \hline \multirow{5}{*}{IGSO} & C06 & 3.9 & 5.2 & 5.4 & 6.4 & 3.1 & 3.8 & 7.7 & 9.8 \\  & C07 & 4.8 & 6.8 & 3.8 & 6.2 & 4.5 & 5.2 & 7.9 & 11.1 \\  & C08 & 4.6 & 6.0 & 4.5 & 4.9 & 3.7 & 4.8 & 7.6 & 9.4 \\  & C09 & 4.3 & 5.9 & 5.1 & 6.9 & 3.3 & 4.5 & 7.7 & 10.6 \\  & C10 & 4.8 & 9.8 & 4.0 & 7.2 & 3.3 & 4.2 & 7.3 & 13.8 \\  & C15 & 5.1 & 7.0 & 4.3 & 5.8 & 3.1 & 3.8 & 7.6 & 10.3 \\  & **mean** & **4.6** & **6.8** & **4.5** & **6.2** & **3.5** & **4.4** & **7.6** & **10.8** \\ \hline \multirow{5}{*}{MEO} & C11 & 10.0 & 9.8 & 4.3 & 4.6 & 3.0 & 3.2 & 11.4 & 11.5 \\  & C12 & 10.1 & 10.0 & 3.7 & 4.4 & 3.4 & 3.5 & 11.5 & 12.4 \\ \cline{1-1}  & C14 & 8.2 & 8.8 & 4.3 & 5.1 & 2.8 & 2.7 & 10.1 & 10.9 \\ \cline{1-1}  & **mean** & **9.4** & **9.5** & **4.1** & **4.7** & **3.1** & **3.1** & **11.0** & **11.6** \\ \hline \hline \end{tabular}
\end{table}
Table 8: Comparison of overlapping arcs precision between strategies 3 and 4 (unit: cm).