## 3 BeiDou PPP Strategy
### Kinematic PPP  
The kinematic PPP performance was also assessed for the modes of BeiDou-only, GPS-only and BeiDou/GPS by processing the daily data from September 24 to September 30 in 2012 at CHDU station. The interval is 30 s. We analyzed the precisions of BeiDou-only, GPS-only and BeiDou/GPS kinematic PPP solutions after convergence. The solutions are compared with the \"ground truth\" of CHDU station. Meanwhile, the convergence time was also analyzed. Figure 8 shows the difference of the results of the BeiDou, GPS and BeiDou/GPS kinematic PPP at CHDU station against the \"ground truth\" in the East, North and Up components on September 24, 2012. Figure 9 shows the satellite numbers and PDOP variations on that day. We can find the following results:  
1. The north component of BeiDou-only kinematic PPP converges faster than the East and Up components at CHDU station. The coordinates difference against the \"ground truth\" for the North and East components of BeiDou-only kinematic PPP after convergences are within \(\pm\)10 cm while that of the up component are within \(\pm\)20 cm.
2. The north component of BeiDou-only kinematic solutions converge as fast as that of GPS-only while the East and Up components converge more slowly than that of GPS-only,  
Figure 7: RMS values of the differences between the BeiDou, GPS, and BeiDou/GPS static PPP results and the “ground truth” in the East, North and Up components from September 4 to September 30 in 2012.  
but as Figure 8 shows, the BeiDou/GPS kinematic PPP converges faster than both BeiDou-only and GPS-only kinematic PPP, especially in the East and North components.
3. As Figure 9 has shown, at least five satellites can be seen at CHDU in every epoch for BeiDou kinematic PPP and the variation PDOP is from 2 to 6. The satellite numbers of combined BeiDou and GPS positioning increase significantly and at least 12 satellites are used in every epoch. The PDOP decreases obviously than that of BeiDou-only and GPS-only cases. As a result, BeiDou/GPS kinematic PPP shows better precision and shorter convergence time than that of BeiDou-only and GPS-only kinematic PPP.  
Figure 8: Differences between BeiDou, GPS, and BeiDou/GPS kinematic PPP solutions with respect to the “ground truth” in the East, North and Up components of CHDU station, respectively on September 24, 2012.  
Figure 10 displays the daily RMS values of the results of the BeiDou, GPS, and BeiDou/GPS kinematic PPP in CHDU against the “ground truth” in the East, North, and Up components from September 24 to September 30 in 2012. We can find the following results:  
Figure 9: Variations of satellite numbers used and PDOP of the BeiDou, GPS, and BeiDou/GPS of CHDU on September 24, 2012.  
1. The accuracy of the horizontal components of BeiDou-only kinematic PPP is within 1.0-2.0 cm except DOY 269 and the accuracy of the vertical component is within 4.0-7.0 cm except DOY 271. The average values of BeiDou-only kinematic PPP in the East, North and Up components are 1.93, 1.57 and 5.86 cm respectively, and those of GPS-only kinematic PPP are 1.99, 1.21 and 6.11 cm, respectively.
2. The accuracy of the horizontal components of BeiDou/GPS kinematic PPP is within 1.0-2.0 cm and that of the vertical component is within 2.0-5.0 cm. The average values of BeiDou/GPS kinematic PPP solutions are 1.14, 0.87 and 3.70 cm, respectively, which significantly improve compared to that of BeiDou-only and GPS-only kinematic PPP, thanks to the increasing of satellite numbers and the improvement of the PDOP.