# Characteristics of BeiDou-3 Experimental Satellite Clocks
## 7 Conclusions  
In this paper, we focus on the characteristics of the improved AFS operated on the latest BeiDou-3 experimental satellites. The two-step method of precise orbit determination is used to obtain the precise clock offsets. Because of the low quality of the measurements caused by the small number of tracking stations, a pre-processing method is necessarily applied to check the original clock offsets.  
The stability of such new clocks is presented and compared with that of GPS, GLONASS, and Galileo. Through the analysis of the clock stability computed from the regional and global stations, we found that subject to the influence of the orbital errors because of the limited number and uneven distribution of the tracking stations, the stability \(3\times 10^{3}\) s to \(8.64\times 10^{4}\) s fluctuates greatly and does not reflect the real stability of the atomic clock. The results based on this show that the PHM clock carried on C32 is approximately \(2.6\times 10^{-14}\) at interval of \(10^{4}\), and has the best stability for any averaging intervals among the BeiDou satellite clocks. Furthermore, the rest of the improved Rb AFS on BeiDou-3 is also superior to the BeiDou-2 at interval of 300 s to \(3\times 10^{3}\) s. For comparison with other navigation systems, the PHM on the BeiDou-3 currently achieves a level of stability comparable to that of the PHM clock of the Galileo and the Rb clocks of the GPS Block IIF, and the improved Rb AFS on BeiDou-3 is comparable to that of the Rb AFS on Galileo, and better than that of the rest of the satellite clocks.  
The analysis of NUFFT indicated that the PHM clock has a great improvement. The amplitude of 12-h (2 CPR) and 8-h (3 CPR) periods is obviously reduced compared with other BeiDou-2 IGSO satellites, and there is no obvious 24-h (1 CPR) period. However, the new Rb clock did not show a  
Figure 8: Median (squares) and interquartile range (IQR) (vertical bars) of the residuals of clock prediction.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**PRN** & **Mean (ns)** & **RMS (ns)** & **PRN** & **Mean (ns)** & **RMS (ns)** \\ \hline C01 & –0.013 & 0.321 & C10 & –0.016 & 0.404 \\ C02 & 0.024 & 0.314 & C11 & 0.002 & 0.334 \\ C03 & –0.044 & 0.242 & C12 & –0.011 & 0.212 \\ C04 & 0.015 & 0.452 & C13 & 0.008 & 0.449 \\ C05 & 0.015 & 0.209 & C14 & –0.040 & 0.241 \\ C06 & –0.010 & 0.373 & C31 & –0.006 & 0.104 \\ C07 & –0.018 & 0.305 & C32 & –0.005 & 0.081 \\ C08 & 0.000 & 0.339 & C33 & 0.017 & 0.157 \\ C09 & 0.014 & 0.232 & C34 & 0.018 & 0.124 \\ \hline \end{tabular}
\end{table}
Table 3: Precision of 1-h sliding linear prediction using 2-h clock offsets.  
substantial improvement. The performance of this new Rb frequency needs further evaluation and analysis in the future.  
The improvement of the clock stability and frequency periods finally contribute to the precision of the short-term clock prediction. For the BeiDou-3 satellites, the RMS of 1-h prediction is less than 0.16 ns.  
As expected, the improved Rb clocks and PHM clock operated on BeiDou-3 show. a better performance than the old BeiDou-2 clocks. The only regret is that there are too few stations that can received the B1 and B3 signal of the experimental satellites. Considering that new types of signals, B1C, B2a, and B2b, are added in BeiDou-3, there is still a lot of work to do with the clock characteristics.  
[PERSON] performed the experiments and wrote the paper; [PERSON] designed the experiments and contributed precise POD product; [PERSON] and [PERSON] supervised and provided the guiding idea for this study.  
This work is supported by the National Nature Science Foundation of China (no. 41674004 and no. 41574030).  
International GNSS Monitoring and Assessment System (iGMAS) and IGS Multi-GNSS Experiment (MGEX) are greatly acknowledged for providing BeiDou data.  
The authors declare no conflict of interest.