## 3 Results and Analysis
### BDS Only PPP
However, for TUVA (Figure 3c), the geometric condition of IGSO and GEO satellites is poor, hence, the contributions of IGSO satellites are weak, and the MEO satellites are most essential for PPP in this case. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**SITE** & **GI** & **GM** & **IM** & **B** \\ \hline GSMQ & 0 & 12.6 & 0 & 0 \\ XMIS & 0 & 29.0 & 0 & 0 \\ TUVA & 25.8 & 45.2 & 16.1 & 3.3 \\ ALL & 2.0 & 21.8 & 1.0 & 0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Percentages of un-convergent sessions of static PPP solutions using different combinations of BDS satellites for the three selected individually and all 20 sites as a whole. Figure 2: Sky-plots of (**a**) GSMQ; (**b**) XMIS; and (**c**) TUVA on DOY 252 in 2014. The statistics of positioning errors for the convergent sessions are summarized in Table 4 for the selected three and all 20 sites, respectively. The standard derivation (STD) and RMS have been used for analysis in this study. For the static solutions, the positioning errors are the differences between the estimated coordinates in the last epoch of each session and the ground truth. Hence, the RMS is actually the root mean square of the positioning errors of all convergent sessions, and the difference between the RMS and STD is used to demonstrate whether there is noticeable positioning bias w.r.t the ground truth. For the kinematic solutions, the epoch-wise coordinates are determined, and the standard STD and RMS are computed with the coordinate differences from the convergent epoch to the last epoch in each session. Hence, the averaged values of STD and RMS from all sessions are used as the corresponding statistical values. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multirow{2}{*}{**Solution**} & \multicolumn{4}{c}{**STD (cm)**} & \multicolumn{4}{c}{**RMS (cm)**} \\ \cline{3-8}  & & **E** & **N** & **U** & **E** & **N** & **U** \\ \hline \multirow{4}{*}{GSMQ} & B & 0.56 & 0.53 & 1.32 & 0.74 & 0.75 & 1.94 \\  & GI & 0.68 & 0.66 & 1.69 & 0.71 & 0.80 & 2.54 \\  & GM & 2.17 & 1.16 & 2.74 & 2.24 & 1.34 & 2.80 \\  & IM & 0.59 & 0.32 & 1.28 & 0.78 & 0.58 & 2.07 \\ \hline \multirow{4}{*}{XMIS} & B & 0.86 & 0.38 & 1.71 & 1.00 & 0.95 & 2.13 \\  & GI & 0.76 & 0.37 & 1.51 & 0.89 & 0.99 & 1.86 \\  & GM & 2.24 & 0.76 & 2.73 & 2.25 & 0.94 & 3.08 \\  & IM & 0.81 & 0.45 & 2.30 & 0.96 & 0.93 & 2.71 \\ \hline \multirow{4}{*}{TUVA} & B & 1.89 & 1.24 & 2.65 & 1.90 & 1.26 & 2.66 \\  & GI & 2.48 & 2.87 & 4.74 & 2.68 & 2.95 & 6.12 \\ \cline{1-1}  & GM & 2.85 & 0.86 & 3.99 & 2.94 & 1.01 & 4.05 \\ \cline{1-1}  & IM & 2.21 & 0.97 & 2.72 & 2.26 & 1.13 & 2.72 \\ \hline \multirow{4}{*}{ALL} & B & 0.78 & 0.57 & 1.82 & 1.05 & 0.76 & 2.38 \\  & GI & 1.10 & 0.70 & 2.12 & 1.29 & 0.91 & 2.81 \\ \cline{1-1}  & GM & 2.41 & 0.99 & 3.02 & 2.60 & 1.10 & 3.35 \\ \cline{1-1}  & IM & 0.84 & 0.49 & 1.86 & 1.11 & 0.70 & 2.59 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Position error statistics of convergent static PPP solutions using different combinations of BDS satellites for the three selected and all 20 sites. Figure 3: Statistics of convergence time in each 100 min and the averaged convergence time for the static BDS only PPP of (**a**) GSMQ; (**b**) XMIS; (**c**) TUVA; and (**d**) all 20 sites. In general, the results of PPP solutions with all BDS satellites are the best. For GSMQ, the positioning accuracy (RMS) is better than 1.0 cm and 2.0 cm in horizontal and vertical component, respectively. However, the positioning accuracy significantly decreases, particular in the east, once observables of IGSO satellites are not used for PPP solutions. Specifically, the degradation is about 1.50 cm, 0.59 cm, and 0.86 cm in the east, north, and vertical component, respectively. The overall statistics of all sites and site XMIS confirm this as well. This demonstrates the largest contribution of IGSO among three types of BDS satellites to the accuracy of static BDS only PPP, and the most contribution is in the east component.