# Initial Positioning Assessment of BDS New Satellites and New Signals
## 4 SPP Performance
### Data Setup and Processing Strategy
To investigate the benefit of BDS-3, 20 out of 54 stations around the Asia-Pacific and Indian Ocean region are selected and compared with BDS-2-only SPP performance. An average of 7-day 3D RMS results for BDS-2-only and BDS-2+BDS-3 are illustrated in Figure 7. A statistical result in RMS and 95% accumulated error are listed in Table 4. It is obvious to see the advantage of BDS-3 in improving horizontal and vertical accuracy. Comparing with global performance in Table 3, the horizontal accuracy is slightly better in the service area of BDS-2, as more satellites are visible. As BDS-2 \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**System**} & \multicolumn{3}{c}{**RMS**} & \multicolumn{3}{c}{**95\%**} \\ \cline{2-7}  & **North** & **East** & **Up** & **North** & **East** & **Up** \\ \hline BDS & 0.90 & 0.64 & 2.16 & 1.69 & 1.22 & 3.89 \\ GPS & 0.80 & 0.47 & 2.12 & 1.50 & 0.95 & 3.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: SPP performance of current BDS and GPS system (in meter). Figure 6: RMS of SPP performance in horizontal (**upper**) and vertical (**lower**) using current BDS constellation (54 stations, one week). performance decreases dramatically beyond the center of the Asia-Pacific region, the contribution of BDS-3 would be more obvious in these regions. What is more, it is interesting to find that for the BDS-2-only case, the positioning accuracy in the North-South component is better than the East-West component, while it is opposite for the BDS-2+BDS-3 or GPS case. This may be due to the reason that 5 GEO satellites of the BDS-2 are located over the equator at longitude of 58.75\({}^{\circ}\)E, 80\({}^{\circ}\)E, 110.5\({}^{\circ}\)E, 140\({}^{\circ}\)E and 160\({}^{\circ}\)E respectively, which would contribute to the DOP value in the North-East component. When BDS-3 satellites are included with a better SISRE, this kind of GEO contribution would decrease. Furthermore, to have a specific observation of the contribution of BDS-3, we take one of the stations, SGOC (6.89\({}^{\circ}\)N, 79.87\({}^{\circ}\)E) as an example. Figure 8 depicts the visible satellite number on January 13, 2019. The average satellite number increases from 10.6 to 15.5 with the help of BDS-3, which would definitely contribute to positioning performance. The corresponding RMS of the SPP result, as shown in Figure 9, would improve from [0.93 m, 1.35 m, 1.82 m] to [0.69 m, 1.11 m, 1.68 m] in the North-East-Up component with a smaller positioning noise due to better PDOP and smaller SISRE of the BDS-3 satellites. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**System**} & \multicolumn{3}{c}{**RMS**} & \multicolumn{3}{c}{**95\%**} \\ \cline{2-7}  & **North** & **East** & **Up** & **North** & **East** & **Up** \\ \hline BDS2-only & 0.96 & 1.10 & 4.13 & 1.91 & 2.08 & 6.05 \\ BDS-2+BDS-3 & 0.72 & 0.56 & 2.24 & 1.34 & 1.07 & 3.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: BDS-2-only and BDS-2+BDS-3 SPP performance around the Asia-Pacific and Indian Ocean region (in m). The results are from one-week of data for 20 stations. Figure 8: Visible satellite number at station SGOC for an elevation angle mask of 10\({}^{\circ}\) on 13 January 2019. Figure 7: RMS of SPP performance for BDS-2-only (**left**) and BDS-2+BDS-3 (**right**) around the Asia-Pacific and Indian Ocean region (20 stations, one week). Please note the different scale of the legend.