## 5 Experiment
### Case 2: 4.8 km Baseline of the HKMW-HKPC Stations in Hong Kong  
Figure 8 shows position errors of successful epochs with different strategies (GPS, GPS + 1 QZS, GPS + 2 QZS, BDS, BDS + 2 QZS, and BDS + GPS + 2 QZS) for the 4.8 km baseline and the curves of the corresponding NOS, ADOP, and Bort are presented in Figure 9. The mean values of NOS, PDOP, ADOP, success rate (both Asrt and Bort) and precision of different strategies are listed in Table 5.  
For the single GPS in case 2, the mean NOS is approximately 9.8, which is 1.7 more than that in case 1. Meanwhile, it can be found that the PDOP, ADOP, Bort, Asrt, and baseline precision (1.545, 0.326, 83.25%, 75.59%, and 1.33 cm, respectively) are all better compared with case 1. Especially, the Asrt of case 2 is two times that of case 1. This is mainly because there are more GPS satellites in case 2, and the length of the baseline in case 2 is shorter, Therefore, more superfluous measurements and fewer residual errors in DD measurements occurred, making the ambiguity resolution more successful. When the NOS of GPS in case 1 and case 2 both come to approximately 10, their Asrt values are almost equal to each other. When the number of QZS used increases from 0 to 2 the PDOP, ADOP, Bort, Asrt, and baseline precision are improved by 0.16, 0.97, 11.77%, 18.99%, and 0.08 cm, respectively. Since case 2 has better GPS resolution conditions (a greater NOS and shorter baseline) and fewer QZS, the improvement effect is smaller compared with case 1. For the single BDS in case 2, the mean NOS in increases to 12.1. The corresponding PDOP, ADOP, Bort, Asrt, and baseline precision are 1.973, 0.176, 99.05%, 99.83% and 1.34 cm, respectively. The PDOP and ADOP are respectively improved by 0.186 \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**System** & **NOS** & **PDOP** & **ADOP** & **Bsrt/\%** & **Asrt/\%** & **Precision/cm** \\ \hline GPS & 8.1 & 1.855 & 0.404 & 89.78 & 37.40 & 2.16 \\ GPS + 1 QZS & 9.1 & 1.727 & 0.308 & 96.92 & 67.26 & 2.16 \\ GPS + 2 QZS & 9.7 & 1.633 & 0.272 & 98.15 & 77.42 & 1.97 \\ GPS + 3 QZS & 10.7 & 1.595 & 0.221 & 99.59 & 94.51 & 1.8 \\ BDS & 9.1 & 2.352 & 0.261 & 98.21 & 96.93 & 1.53 \\ BDS + 2 QZS & 10.9 & 2.142 & 0.220 & 99.63 & 99.42 & 1.40 \\ BDS + 3 QZS & 11.6 & 2.069 & 0.199 & 99.88 & 99.61 & 1.41 \\ BDS + GPS + 3 QZS & 19.8 & 1.115 & 0.106 & 100.00 & 100.00 & 1.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: NOS, PDOP, ADOP, success rate and precision of different strategies for the 12.5 km baseline. and 0.013, and Asrt is increased to 99.99% when 2 QZS were added. However, the baseline precision is still 1.34 cm without improvement because the Asrt of the single BDS is very high and little room is available for improvement if only two QZS are added. Undoubtedly, the integrated BDS/GPS/QZSS still has the best performance of the 6 indicators; the Asrt is 100% and baseline precision is improved to 1.03 cm. In case 1, the Bsr of GPS is not consistent with Asrt, especially when the NOS is small. Section 4.2 previously mentioned that the Bsr could become inaccurate when DD residuals became larger with the increase of the baseline length, which leads to low precision of the float ambiguities. However, for the single GPS in case 2, its Bsr is close to Asrt because more common satellites improved the quality of float ambiguities and increases the success rate of the ambiguity resolution. Generally, both experiments indicate that not only the availability, PDOP and ADOP are well promoted, but also the success rate and baseline precision are effectively improved when GPS or BDS is augmented by QZSS. When more QZS are used, PDOP and ADOP decrease, the success rate and accuracy become higher and better. In addition, the performance of the single BDS in the two cases both precede that of the single GPS or even GPS/QZSS excluding PDOP because BDS has the advantages of NOS and satellites elevation.