# Evaluation of Network RTK Positioning Performance Based on BDS-3 New Signal System
## 4 Experiment and Analysis  
### Analysis of DD Atmospheric Correction at Reference Stations  
The double-difference atmospheric delay, extracted after the reference station network baseline is fixed, is the premise of regional atmospheric modeling interpolation. Therefore, this section takes the WH04-HG02 baseline as an example to analyze the accuracy of the extracted double-difference atmospheric delay. The analysis period is selected from 13:30:00 to 15:30:00 (GPS time), and the reference satellite in this period is B40. A total of 10 non-reference satellites participated in the calculation during this period. Figure 4 shows the double-difference ionospheric and tropospheric delay time series solved by using the combination of two kinds of frequency signal combinations. In Figure 5, residual time series corresponding to two kinds of frequency signal combinations with fixed ambiguity are given according to pseudo-range and phase, respectively. Table 3 shows the root mean square (RMS) values of the corresponding index time series for each satellite of the two types of frequency signal combinations. The mean value of the RMS of each satellite under each index is calculated as the final statistical value of the corresponding index of this frequency signal combination and listed in the last line of Table 3. Figure 6 shows the mean histogram of the double-difference ionospheric and tropospheric RMS values of all  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Schemes** & **Items** & **Description** \\ \hline \multirow{8}{*}{Network RTK} & Observations & Double-difference non-combined model \\  & Sampling interval & 1 s \\  & Elevation mask & 10\({}^{\circ}\) \\  & Weighting & Priori precision 0.003 m for phase and 0.3 m for code; Elevation-dependent weight: \\  & & P/sin(el) \\  & Relativistic effect & IERS Conventions 2010 \\  & Satellite phase center & PCO and PCV for GPS and only PCO corrected for BDS using isgs14.4 tx \\  & Receiver phase center & PCO and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and BDS using isgs14.4 tx \\  & & Season and PCV corrected for GPS and only PCO corrected for BDS using isgs14.4 tx \\  &  
satellites under the two kinds of frequency signal combinations of the WH04-HG02 baseline based on the last line of Table 3.  
As can be seen from Figure 4, both ionospheric delay and tropospheric delay change slowly, and the atmospheric change of each satellite shows a trend related to elevation angle; that is, the atmospheric fluctuation is larger under low elevation. In addition, the overall variation trend of atmospheric delay extracted from the combination of the two types of frequency points is basically similar. It can be seen from Figure 5 that the pseudo-range residual after the ambiguity is fixed within 2 m in most periods, and the phase residual is within 2 cm. Table 3 summarizes the RMS statistics of each indicator. It can be seen that the atmospheric solution accuracy of the B1C+B2a combination is slightly better than that of the B1I+B3I combination, and the statistical results of each indicator are basically consistent. The final RMS values of the six indicators of ionosphere, troposphere, and pseudo-range/phase post-test residuals were: B1C+B2a (0.016 m, 0.032 m, 0.704 m, 0.586 m, 0.0053 m, 0.0026 m); B1I+B3I (0.019 m, 0.037 m, 0.871 m, 0.699 m, 0.004  
Figure 5: (**a**) The residuals of pseudo-range and phase observations for BIC+B2a combination of BDS-3 in WH04-HG02. (**b**) The residuals of pseudo-range and phase observations for B1I+B3I combination of BDS-3 in WH04-HG02.