# Evaluation of Network RTK Positioning Performance Based on BDS-3 New Signal System
## 4 Experiment and Analysis
### Accuracy Analysis of Regional Atmosphere Modeling and Interpolation  
The modeling accuracy of the regional double-difference atmospheric delay is a key factor affecting the accuracy of the network RTK service. Therefore, based on the analysis period in Section 4.1, the SC17 site is selected as the rover test station in this section. The atmospheric correction of this site is interpolated according to the modeling strategy mentioned above. At the same time, the WH04-SC17 baseline was calculated, and the double-difference atmospheric information was directly extracted as the reference value (JX), and the modeling value (CZ) was compared with its accuracy. Figure 7 takes the B33 satellite as an example to show the time series of atmospheric modeling values and reference values under the two frequency signal combinations. Table 5 shows the RMS values of corresponding indexes for all satellites in the test period under the combination of two types of frequency signals. The mean value of RMS of each satellite under each index is taken as the final statistical value of the corresponding index of this frequency signal combination and listed in the last column of Table 5. Figure 8 draws the histogram of the mean RMS of atmospheric modeling values and reference values of station SC17 under different frequency signal combinations given in the last column of Table 5. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Baseline** & **B1C+B2a** & **B11+B31** \\ \hline WH04-HG02 & 99.9\% & 99.7\% \\ WH04-HG05 & 99.9\% & 99.2\% \\ WH04-W7H02 & 99.6\% & 96.3\% \\ WH04-XN01 & 98.4\% & 97.3\% \\ HC02-HG05 & 99.9\% & 98.6\% \\ HG02-XN01 & 97.9\% & 98.2\% \\ WH02-XN01 & 99.3\% & 98.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The fixed success rate of the baselines in reference networks. Figure 7: Comparison of atmospheric modeling value and reference value of B33 satellite at SC17. Station (CZ modeling value/JX reference value/DIFF mutual difference of two values). According to the RMS of each satellite modeling deviation value (DIFF) in Table 5, it can be seen that the interpolation accuracy of atmospheric modeling is about 1 cm. The following two conclusions can be drawn from Figure 7: Firstly, the time series of atmospheric modeling value and the reference value of the B33 satellite under the combination of two frequency signals are basically consistent, but the modeling deviation shows a trend of increasing with the decrease of elevation angle. This is consistent with the law of atmospheric correction accuracy and elevation angle presented in Section 4.1, which also confirms the reasonability of baseline weighting based on elevation angle in the modeling interpolation strategy in Section 2.2 of this paper. In addition, the modeling deviation of the B11+B3I combination is obviously greater than that of the B1C+B2a combination, which is consistent with the statistical comparison results of atmospheric correction accuracy between the two combinations in Section 4.1. The rest of the satellites show the same pattern, not shown in this article for reasons of space. The following two conclusions can be drawn from the mean RMS of each indicator shown in Figure 8: Firstly, the atmospheric modeling value (CZ) is smoother than the baseline reference value (JX). This is because the regional atmospheric modeling is based on the weighted comprehensive results of multiple  
Figure 8: Comparison of mean RMS between atmospheric modeling values and reference values under different frequency signal combinations at Station SC17.