# Real-Time Precise Point Positioning during Outages of the PPP-B2b Service
## 3 Experiments and Results
### Positioning Quality Degradation over Time  
#### 3.3.1 Accuracy of the Real-Time PPP-B2b Positioning  
A simulated kinematic experiment was conducted with PPP-B2b corrections and real-time observations at five stations. The specific processing strategies adopted in the PPP and locations of the stations are listed in Tables 4 and 5, respectively. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Extension Time/s**} & \multicolumn{3}{c}{**BDS-3 MEO**} & \multicolumn{3}{c}{**BDS-3 IGSO**} & \multicolumn{3}{c}{**GPS**} \\ \cline{2-9}  & **R/m** & **A/m** & **C/m** & **R/m** & **A/m** & **C/m** & **R/m** & **A/m** & **C/m** \\ \hline
30 & 0.14 & 0.23 & 0.20 & 0.14 & 0.29 & 0.24 & 0.07 & 0.29 & 0.25 \\
60 & 0.14 & 0.23 & 0.21 & 0.15 & 0.29 & 0.24 & 0.07 & 0.32 & 0.26 \\
120 & 0.15 & 0.24 & 0.21 & 0.15 & 0.30 & 0.25 & 0.08 & 0.34 & 0.27 \\
180 & 0.15 & 0.24 & 0.21 & 0.15 & 0.30 & 0.25 & 0.08 & 0.35 & 0.28 \\
300 & 0.15 & 0.25 & 0.22 & 0.15 & 0.30 & 0.26 & 0.09 & 0.38 & 0.29 \\
600 & 0.16 & 0.26 & 0.23 & 0.16 & 0.31 & 0.27 & 0.11 & 0.45 & 0.33 \\
1200 & 0.17 & 0.29 & 0.25 & 0.18 & 0.34 & 0.29 & 0.13 & 0.58 & 0.40 \\
1800 & 0.18 & 0.31 & 0.27 & 0.19 & 0.35 & 0.31 & 0.18 & 0.67 & 0.45 \\
3600 & 0.20 & 0.36 & 0.30 & 0.22 & 0.38 & 0.35 & 0.23 & 0.80 & 0.58 \\ \hline \end{tabular}
\end{table} 
Table 1: Mean RMSE of the PPP-B2b orbit products recovered with extension corrections using the GBM orbit products as a reference during DOY 192–198 in 2022. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Extension Time/s**} & **BDS-3 MEO** & **BDS-3 IGSO** & **GPS** \\ \cline{2-5}  & **Clock/ns** & **Clock/ns** & **Clock/ns** \\ \hline
30 & 1.75 & 1.88 & 3.89 \\
60 & 1.79 & 1.94 & 3.96 \\
120 & 1.83 & 2.01 & 4.05 \\
180 & 1.86 & 2.07 & 4.10 \\
300 & 1.91 & 2.14 & 4.19 \\
600 & 2.01 & 2.27 & 4.35 \\
1200 & 2.16 & 2.44 & 4.57 \\
1800 & 2.27 & 2.57 Figure 12 shows the mean RMSE of the real-time PPP-B2b positioning errors for the five stations during DOY 355-361 in 2022. The errors in the north and east directions for the five stations were less than those in the up direction. The three-dimensional (3D) errors of the positioning results for stations located in China, i.e., BJ01, JFNG, and HKSC, were in the range of 0.11-0.14 m, while those for stations located in the northwest and outside of China, i.e., KSKT and MSSA, were in the range of 0.27-0.34 m. These results show that the real-time positioning accuracy varies from region to region, and the positioning accuracy is better in areas near the center of China. This is because different regions have different numbers of observable satellites that can be used for PPP-B2b corrections, and different observation geometries. The number of available satellites with PPP-B2b correction and the observation geometries of these satellites in China are better than those in the surrounding areas [20]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Processing Strategy** \\ \hline System & BDS-3 + GPS \\ Frequencies & GPS L1/L2 and BDS-3 B1I/B3I \\ Observation data & Real-time data stream \\ Satellite orbit and clock & B2b corrections + Broadcast ephemeris \\ Ionospheric delay & Ionosphere-free linear combination with dual frequency \\ Tropospheric delay & Estimation zenith total delay and horizontal gradient \\  & parameters \\ Antenna PCO/PCV & Isg14.atx \\ Elevation cut-off angle & \(7^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Processing strategies for the simulated kinematic PPP-B2b experiment. Figure 12: Mean RMSE of the real-time PPP-B2b positioning errors of the simulated kinematic PPP-B2b solutions for the five stations in the north, east, and up directions, and 3D coordinates, during DOY 355-361 in 2022.