## 4 Result and Analysis
### BDS-2 and BDS-3 Broadcast Clock Offsets
Figure 5 depicts the standard deviations (STD) of the differences in average BMP clock values between BDS-2 and BDS-3. The STD of GFZ, WHU and SHA are all better than 1 ns during the whole data test period. In order to reduce the impact of the inconsistency of the datum of broadcast clock offsets on the assessment of BDS-2 and BDS-3 signal-in-space accuracy and SPP, [PERSON] and [PERSON] [12] attribute this bias to satellite-dependent TGD bias of the BDS broadcast ephemeris, and estimate TGD bias to weaken this impact. Even if TGD bias is used to correct this inconsistency, its residuals will still affect signal-in-space accuracy and SPP. To ensure the objectivity and stability of the assessment of signal-in-space accuracy, we regard BDS-2 and BDS-3 as two systems, and solve separately their average BMP clock values of all satellites to get the error of the broadcast clock offset. Figure 6 depicts the BDS-2 and BDS-3 clock errors for the broadcast clock offsets, in which the precise clock offsets provided by GFZ, WHU and SHA are regarded as the reference values, respectively. From Figure 6, we can get the clock errors of BDS-2 and BDS-3 are better than 10 ns and 5 ns, respectively. As illustrated in the previous section, the precise products are missing on some days, the corresponding clock errors obtained are also missing. In order to display the accuracy and stability of the broadcast clock offsets of each BDS satellite, this contribution gives the time series of STD and root mean square (RMS) error of BDS clock errors. From the perspective of STD, the STD of BDS clock errors calculated by GFZ, WHU and SHA performs great consistency. From Figure 7, the 35-day STDs of BDS-2 clock errors calculated by GFZ, WHU and SHA are all better than 2 ns, except for a few days. With the upgrade of BDS-3 satellite hardware technology and the development of precise orbit determination  
Figure 4: The time series of average broadcast-minus-precise clock values of BDS-2 and BDS-3 and its differences. (POD) algorithms, the 35-day STDs of BDS-3 clock errors are better than 1 ns, except for C45 and C46. The time of C45 and C46 satellites in orbit is very short because they have just been launched. Some GNSS tracking stations cannot receive the observation data of C45 and C46, the available observation data used for POD is limited. Therefore, the accuracy and stability of orbit and clock offsets are slightly worse than other BDS-3 satellites, and the corresponding STD performs worse. Figure 5: The STD of the average broadcast-minus-precise clock values differences between BDS-2 and BDS-3. Figure 6: The BDS-2 and BDS-3 clock errors between broadcast clock offsets and the precise clock offsets obtained from GFZ, WHU and SHA. Now turn to the RMS of BDS clock errors, which is shown in Figure 8, the BDS-3 has improvement in terms of RMS compared with BDS-2. The RMS of BDS-3 clock errors are better than 3 ns, except for individual satellites. From the perspective of the results obtained by three ACs, the RMS of three ACs performs some difference in C01, C11, C14, C38 and C39 (WHU has not provided the precise products after C37, so there are no assessment results after C37). Although the datum of the satellite clock offsets can be eliminated by double difference, the error of the broadcast clock offset will absorb the new datum of the reference clock. Because the processing strategies of precise clock offsets adopted by different ACs are different, there are also differences in the new datum of the reference clock. Therefore, different ACs have poor RMS consistency but with the great STD consistency. Therefore, it is more scientific and rigorous to assess broadcast ephemeris with precise products solved by different ACs. Figure 7: The STD time series of BDS clock errors between broadcast clock offsets and the precise clock offsets obtained from GFZ, WHU and SHA. In order to show the accuracy of BDS broadcast clock offsets more intuitively, Table 4 illustrates the mean STD and RMS statistics of broadcast clock errors for each BDS satellite.