## 5 Conclusions  
Based on BDS/GPS data in CMONOC, we analyzed the positioning accuracy of BDS, GPS and BDS/GPS combined solutions, presented the status of observing and the quality of observation of BDS satellites, depicted the spatial pattern of the position differences between BDS and GPS results in China, discussed the accuracy and its prospect on crustal deformation domain for velocity field derived from BDS data, and deduced the influencing factors on determining the accuracy of BDS positioning. Some conclusions can be drawn as follows. The SNR and MPD are highly correlated with the elevation angles of satellites, and the higher the elevation angle, the lower the MPD. The MPD for different frequencies are similar with each other, while the SNR are significantly distinct. BDS satellites have similar MPD with GPS satellites. The SNR for IGSO and MEO sets of BDS satellites are similar with GPS satellites, while it is lower than any other satellites for GEO satellites. The accuracy of BDS positioning results is lower than GPS and BDS/GPS results, with values being 7 and 22 mm on horizontal and vertical components, respectively. The horizontal accuracy for BDS position time series declines with the rising of the latitude in CMONOC, while the vertical one shows spatially random features. The accuracy of velocity field derived from BDS position time series with data volume being about 2.5 years, are 1.2, 1.5, and 4.1 mm/year for north, east and up components. The annual signals with remarkable amplitudes can be emerged and well estimated in BDS position time series. It is insufficient to precisely depict vertical crustal movements in China mainland by 2.5 years of BDS observations. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Title**} & \multicolumn{2}{c}{**North (mm)**} & \multicolumn{2}{c}{**East (mm)**} & \multicolumn{2}{c}{**Up (mm)**} \\ \cline{2-6}  & **Mean** & **RMS** & **Mean** & **RMS** & **Mean** & **RMS** \\ \hline Different satellite ephemeris & \(-0.1\) & 6.3 & \(-0.7\) & 7.6 & \(-0.5\) & 23.5 \\ With and without MEO satellites & 0.4 & 12.0 & 5.1 & 14.1 & 0.0 & 42.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The mean and RMS of baselines differences between BDS positioning results. The position differences originated from different BDS ephemeris are at the same level with the accuracy of BDS positioning results, indicating that the accuracy of ephemeris is an important factor in determining the accuracy of BDS positioning results. Compared with the results without four MEO satellites, the accuracy of BDS positioning results is doubled with four MEO satellites included in the BDS constellation, thus indicating the other factors in determining the low accuracy of BDS positioning is the small amount of MEO satellites. With the decoding of more MEO satellites and the gradual accomplishing of the MEO constellation, we will look further into the contribution of MEO satellites on the accuracy of BDS positioning results. The following are available online at [[http://www.mdpi.com/1424-8220/18/10/3353/1](http://www.mdpi.com/1424-8220/18/10/3353/1)]([http://www.mdpi.com/1424-8220/18/10/3353/1](http://www.mdpi.com/1424-8220/18/10/3353/1)), Figure S1: Sky plots (azimuth vs. elevation) for BDS and GPS satellite systems at YNSM on the third day of 2017. (a) BDS; (b) GPS; (c) BDS and GPS; Figure S2: The MPD variations with respect to the elevation angle of satellites. The blue is for the C01 satellite, the green is for the C07 satellite, the red is for the C12 satellite, and the black is for the G11 satellite; Figure S3: The SNR variations with respect to the elevation angle of the satellite. The meanings of the different colors in the diagram are the same as Figure S3; Figure S4: The residual position time series at different stations for BDS, GPS and GPS/BDS combined solutions, respectively. (a) Station AHBB, (b) Station QHGC, (c) Station CHUN, and (d) Station XJBY. [PERSON] and [PERSON] initialized the idea and drafted the manuscript.