# Initial Positioning Assessment of BDS New Satellites and New Signals
## 4 SPP Performance
### New Signal of B1c and B2a  
The positioning results in the previous sub-section are based on B1I signal. In this subsection, we will investigate the SPP performance using the new BDS signals B1c and B2a. Due to the data limitations, only nine out of 54 IGS stations are able to receive the B2a signal, and only four stations are able to receive the B1c signal. As B1c and B2a signals are only transmitted by BDS-3 satellites, for a better comparison, only data of BDS-3 satellites are used in this section. Similar with previous analysis, an average of 7-days of SPP RMS and 95% accumulated error on B1I, B1c and B2a are presented in Table 5, and the RMS of SPP results at each station are plotted in Figure 10. When comparing the different frequencies, one can see that SPP accuracy on B1I and B1c frequency is at a similar level. It seems that horizontal error on the B1I frequency is slightly better than B1c, while B1c shows slightly better performance in the vertical. For the B2a frequency, it presents a much worse result than the B1I or B1c frequency, which may possibly be attributed to the inaccurate ionosphere correction on B2a.  
To investigate the detailed positioning performance of new signals, we choose the station of BSHM (32.78\({}^{\circ}\)N, 35.02\({}^{\circ}\)E) for analysis. Figure 11 depicts the satellite number and PDOP value of BDS-3 on 13 January 2019. As we can see, the number of visible satellites for BDS-3 at station BSHM is between 4 and 7. With a PDOP threshold of 6, the positioning availability is about 79.3%.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency**} & \multicolumn{3}{c}{**RMS**} & \multicolumn{3}{c}{**95\%**} \\ \cline{2-7}  & **North** & **East** & **Up** & **North** & **East** & **Up** \\ \hline B1I & 0.87 & 0.71 & 2.92 & 1.65 & 1.32 & 4.89 \\ B1c & 0.91 & 0.74 & 2.73 & 1.81 & 1.51 & 4.52 \\ B2a & 1.24 & 0.80 & 4.27 & 2.27 & 1.55 & 6.49 \\ \hline \hline \end{tabular}
\end{table}
Table 5: SPP performance of B1I, B1c and B2a (in meter). The results are from one-week of data.  
Figure 9: SPP comparison of BDS-2 only (green) and BDS-2+BDS-3 (red) at station SGOC in North (upper), East (middle) and Up (lower) component.  
Daily SPP performance of B1I, B1c and B2a at station BSHM are evaluated, as shown in Figure 12. Similar conclusion can be found that B1I and B1c performs a similar positioning accuracy, while it is much worse on B2a. Furthermore, it seems that positioning error dispersion on B1I is much noisier than B1c and B2a. To validate it, the pre-fit observation minus corrections (OMC) of B1I, B1c and B2a are calculated using true coordinates, which are illustrated in Figure 13. Obviously, the OMC noise on B1c and B2a is much smaller than B1I. This is different from the BDS-3e satellite, whose B1c noise is at the same level as B1I [15]. However, although the B2a signal performs the smallest noise, the OMC on B2a shows a much more dispersive residual, thus resulting in the worst positioning error. This may be due to the inaccurate model of ionosphere correction, which has a more serious impact on B2a rather than B1I or B1c.  
Figure 11: Satellite number and PDOP of BDS-3 at station BSHM.  
Figure 10: RMS of SPP performance of B1I, B1c and B2a at horizontal (**upper**) and vertical (**lower**) component (BDS-3-only, one week).