# Evaluation of Network RTK Positioning Performance Based on BDS-3 New Signal System
## 4 Experiment and Analysis
### Analysis of Positioning Performance of Network RTK Terminal  
The service performance of network RTK is finally reflected in the positioning effect of the terminal. Therefore, this section takes the GPS system as reference to analyze the positioning effect of network RTK of SC17 station under GPS, BDS-2, BDS-3 [B1I+B3I], BDS-3 [B1C+B2a], and BDS-2/3. Figure 9 shows the number of satellites and the distribution of position dilution of the precision (PDOP) value of Station SC17. It can be seen that the number of satellites and the distribution of PDOP value of BDS-3 are better than that of BDS-2 in most periods of time because BDS-3 is currently operating in full constellation and MEO constellation configuration is better. In addition, the visible satellite number and PDOP value distribution of the BDS-3 system are also better than that of the GPS system most of the time. Figure 10 shows the positioning results of fixed solutions under five design schemes of Site SC17. Table 6 shows the baseline fixation rate and RMS statistics of fixed solutions based on the schemes in Figure 10.  
It should be noted that the single GPS is used as a performance reference, and the network RTK algorithm processing is completely consistent with other solutions. It uses L1+L2 as the main frequency signals for the reference station baseline calculation. In order to ensure the accuracy of the baseline calculation. The judgment conditions for the fixed baseline setting of the reference station are also: the minimum number of satellites with fixed ambiguity in narrow lanes is not less than five, or the number of fixed satellites accounts for more than 60% of the number of satellites involved in the solution. At least one of the two conditions is met. The specific parameter processing strategy of the server and terminal is shown in Table 2.  
Figure 9: Number of tracked satellites (**top**) and their PDOP values (**bottom**) for Station SC17.  
As can be seen from Figure 10, the horizontal and elevation error of any combination of GPS, BDS-2, BDS-3 [B1I+B3I], BDS-3 [B1C+B2a], and BDS-2/3 fixed solutions are basically within 3 cm and 5 cm, respectively. According to the RMS statistics given in Table 6, the horizontal accuracy is basically within 1 cm, the elevation accuracy is basically within 2 cm, and the fixed rate is above 95%. According to the statistical results of the fixed rate and RMS for each scheme given in Table 6, the following rules can be obtained: the positioning accuracy of BDS-2 is relatively poor; GPS is superior to the BDS-2; any frequency signal combination of BDS-3 is better than GPS and BDS-2. The BDS-3 new signal combination (B1C+B2a) was slightly better than the transition signal combination (B1I+B3I). Due to the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Schemes** & **Fix Rate** & **E (m)** & **N (m)** & **U (m)** \\ \hline GPS & 98.6\% & 0.0054 & 0.0062 & 0.0173 \\ BDS-2 & 97.5\% & 0.0063 & 0.0072 & 0.0202 \\ BDS-3 [1I+3I] & 99.4\% & 0.0055 & 0.0057 & 0.0170 \\ BDS-3 [1C+2a] & 99.8\% & 0.0049 & 0.0047 & 0.0162 \\ BDS-2/3 & 100\% & 0.0047 & 0.0040 & 0.0139 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The fixed rate of baseline and positioning RMS of fixed solution from different schemes for Station SC17.  
Figure 10: The coordinate error of NRTK fixed solution from different schemes for Station SC17.  
large number of satellites involved in the calculation, the positioning accuracy and fixed rate of the BDS-2/3 scheme in all directions are generally superior to other combinations. Relevant laws can also be reflected in the positioning time series of each scheme plotted in Figure 10.