## 6 Conclusions  
This study assesses the clock performance for the BDS-3 basic system with 18 MEO satellites (8 with PHM and 10 with RAFS), in terms of frequency accuracy, daily drift rate, and stability at the averaging time of 300 s, 10,000 s, and 1 day. First orbits and clocks of XRS products are compared to WUM and IGS final products. The GPS result shows the accuracy of orbits and clocks is comparable to the WUM products. The BDS orbits comparison result of XRS products with respect to WUM products  
Figure 15: HDEV of the differenced frequency data for BDS-3 MEO PHM and Galileo PHM satellites with respect to KOUR station. is in the order of decimeter magnitude and the clock STD is about 0.2 ns, which are worse than the results of GPS and Galileo satellites. We give the possible reason. Then, we develop a data auto-editing procedure to preprocess clock data and assess the clock performance at each continuous arc. With the outliers excluded and day boundary problem solved using the specific strategy, the clean frequency data can be derived. The ODTS noise is derived by four stations attached to high-precision AHM. The average values of 10,000 s and 86,400 s stability are \(1.13\times 10^{-14}\) and \(2.68\times 10^{-15}\), respectively, where the best results are between MGUE and KOUR stations with the values being \(8.93\times 10^{-15}\) and \(1.85\times 10^{-15}\), respectively. These results indicate that the level of ODTS noise can be basically neglected when processing the performance assessment of GNSS clocks. BDS-3 clock performance is compared with that of GPS BLOCK IIF RAFS, Galileo PHM, and BDS-2 RAFS satellites. In terms of frequency accuracy, the average values of BDS-3 RAFS and PHM are \(2.29\times 10^{-11}\) and \(1.48\times 10^{-11}\), respectively, where the RAFS is comparable to BDS-2, and the PHM is comparable to GPS with the value of \(9.30\times 10^{-12}\) and Galileo with the value of \(9.37\times 10^{-12}\). As for the frequency daily drift rate, the average value of BDS-3 RAFS is \(1.48\times 10^{-13}\), which is slightly worse than BDS-2 MEO satellites with the value of \(9.04\times 10^{-14}\). The mean value of BDS-3 PHM is \(1.44\times 10^{-15}\) except C34 and C35, which is significantly better than the \(2.22\times 10^{-14}\) of GPS and basically comparable to the \(1.25\times 10^{-15}\) of Galileo. In terms of the stability at 300 s averaging time, the BDS-3 RAFS value is \(9.43\times 10^{-14}\), which is better than BDS-2 satellites. The BDS-3 PHM value is \(9.07\times 10^{-14}\), which is slightly better than the GPS value of \(8.91\times 10^{-14}\) and slightly worse than the Galileo value of \(7.08\times 10^{-14}\). The stability at 300 s averaging time among GPS IIF RAFS, Galileo PHM, and BDS-3 satellites is basically comparable. The 10,000 s stability of BDS-3 RAFS is \(2.49\times 10\)-14, which is better than BDS-2 and GPS satellites. The BDS-3 PHM value is \(2.32\times 10^{-14}\), which is better than the GPS value of \(4.14\times 10^{-14}\) and slightly worse than the Galileo value of \(1.77\times 10^{-14}\). As for the stability of 86,400 s, the BDS-3 RAFS is \(8.64\times 10^{-15}\), which is better than BDS-2 satellites. The BDS-3 PHM is \(5.28\times 10^{-15}\), which is slightly worse than the GPS value of \(4.52\times 10^{-15}\) and better than the Galileo value of \(5.57\times 10^{-15}\). Therefore, the clock performance of BDS-3 PHM is basically comparable to Galileo satellites and that of BDS-3 RAFS is better than BDS-2. [PERSON] proposed the initial idea of this study and supervised the experiments. [PERSON] performed the experiments and wrote the paper. [PERSON] provided the XRS products. [PERSON], [PERSON], and [PERSON] reviewed the paper. This research was funded by National Natural Science Foundation of China (Grant Nos. 41874041, 41704035, 41904039) and by State Key Laboratory of Geo-Information Engineering, NO. SKLGIE2018-M-2-1. The authors are grateful to iGMAS and MGEX for providing data and products for analysis. The authors declare no conflict of interest.