## 5 Experiment
### Case 1: 12.5 km Baseline of HKQT-HKLM Stations in Hong Kong  
Figure 6 shows position errors of successful epochs (Asrt relevant) with different strategies (GPS, GPS + 1 QZS, GPS + 2 QZS, GPS + 3 QZS, BDS, BDS + 2 QZS, BDS + 3 QZS, and BDS + GPS + 3 QZS) for the 12.5 km baseline and Figure 7 presents the curves of the corresponding NOS, ADOP, and Bstr. The baseline deviation of failure epochs is up to several decimeters and is usually not accepted, so only the baseline precision results of successful epochs are counted. The mean NOS, PDOP, ADOP, success rates (both Bstr and Asrt) and precision of different strategies are presented in Table 4, which shows that the trend of PDOP and ADOP has a negative correlation with that of the NOS. The mean GPS PDOP and ADOP decrease by 0.26 and 0.18, while the number of QZS increases from 0 to 3. Similarly, the mean PDOP and ADOP of BDS decrease by 0.28 and 0.06, of which the improvement is less than that of GPS. There is an obvious phenomenon shown in Tables 2 and 4, which indicates that BDS has more satellites but poorer PDOP results compared with GPS. This is mainly because GPS satellite positions are more scattered and cause a larger geometric volume of the GPS constellation, which contributes to a better PDOP of GPS. However, BDS has more visible satellites than GPS and most of the BDS satellites are synchronous orbit satellites with higher elevation. Accordingly, BDS and BDS/QZSS perform better in ADOP, success rate, and baseline precision than the GPS and GPS/QZSS.  
Figure 5: Baselines’ distribution among Hong Kong stations.  
Figure 6: _Cont._  
Figure 7: Mean NOS, ADOP, and bootstrapped success rates of different strategies: **(a)** GPS; **(b)** GPS + 1 QZS; **(c)** GPS + 2 QZS; **(d)** GPS + 3 QZS; **(e)** BDS; **(f)** BDS + 2 QZS; **(g)** BDS + 3 QZS and **(h)** BDS + GPS + 3 QZS for the 12.5 km baseline.  
For the single GPS, it is difficult to obtain a high success rate result for a baseline over 10 km because ionospheric and tropospheric errors cannot be completely eliminated. Meanwhile, the baseline only has 8.1 common satellites. In this condition, the mean Asrt of the single GPS is only 37.40% and many interruptions that represent failure epochs exist, as seen in Figure 6a. Aided by different numbers of QZS, the mean Asrt is increased to 67.26%, 77.42%, and 94.51%, during which the respective curve interruptions in Figure 6b-d gradually decrease. Therefore, the QZSS can greatly improve the success rate of GPS baseline resolution. The precision of successful epochs is not changed obviously when aided by only one QZS. With more aided QZS components, the number of successful epochs increases, and the performance of GPS/QZSS is improved palpably. The baseline precision of successful epochs is also improved from 2.16 cm to 1.8 cm. Compared with GPS/QZSS, the success rate promotion with integrated BDS/QZSS is not so obvious. BDS has advantages in NOS and satellite elevation in the Asia-Pacific region; hence Asrt of the single BDS for 12.5 km baseline is up to 96.93%. The Asrt increases to 99.61% when three QZS were added into the BDS baseline solution under the condition that little room is available for improvement of Asrt. This means QZSS can effectively improves BDS's Asrt and makes it closer to 100%. Furthermore, the BDS baseline precision is also improved by 0.12 cm. Therefore, the QZSS shows comprehensive improvement in the performance of GPS and BDS carrier phase baseline resolution, especially for GPS ambiguity resolution success rate. Finally, for the combination of BDS/GPS/QZSS, the NOS is near 20, the ADOP is only approximately 1.1 and both Bort and Asrt reach 100%. As a result, the combination of BDS/GPS/QZSS certainly has the highest accuracy of 1.25 cm.