## 4 Result and Analysis  
### BDS-2 and BDS-3 Broadcast Clock Offsets  
To analyze and evaluate the accuracy of BDS-2 and BDS-3 broadcast clock offsets, we use the algorithm in Section 2.1 to evaluate the broadcast clock offsets. When calculating the error of the broadcast clock offsets, the average BMP clock values of satellites of the same constellation is subtracted to eliminate the datum of the broadcast clock [26]. Selecting the same reference satellite or calculating average BMP clock values of satellites of the same constellation cannot eliminate the datum of the broadcast clock under the condition that the datum of precise clock offsets is unified, which can indirectly prove that the datum of broadcast clock offsets for BDS-2 and BDS-3 are inconsistent. Unfortunately, the average BMP clock values of BDS-2 and BDS-3 are not equal. Figure 4 shows the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Station** & **Agency** & **Receiver** & **Manufacturer** & **Antenna** \\ \hline POTS & IGS MGEX & JAVAD TRE\_3 & JAVAD & JAVRINGANT\_GST \\ SGOC & IGS MGEX & JAVAD TRE\_3 & JAVAD & JAVRINGANT\_GST \\ ULAB & IGS MGEX & JAVAD TRE\_3 & JAVAD & JAVRINGANT\_GST \\ URUM & IGS MGEX & JAVAD TRE\_3 & JAVAD & JAVRINGANT\_GST \\ WUH2 & IGS MGEX & JAVAD TRE\_3 & JAVAD & JAVRINGANT\_GST \\ KRGG & IGS MGEX & TRIMBLE ALLOY & TRIMBLE & LEIAR25.R4 \\ MCHL & IGS MGEX & TRIMBLE & LICIAR25.R4 \\ KTTG & IGS MGEX & SEPTOLAK3 & TRIMBLE & TRM59800.00 \\ DJG & IGS MGEX & SEPT POLARX5 & SEPTENTRO & JAVRINGANT\_DM \\ PTGG & IGS MGEX & SEPT POLARX5 & SEPTENTRO & TRM59800.00 \\ BJF1 & iGMAS & CETC-54-GMR-4016 & CETC 54 & LEIAR25.R4 \\ BRCH & iGMAS & CETC-54-GMR-4016 & CETC 54 & NOV750.R4 \\ ICUK & iGMAS & CETC-54-GMR-4016 & CETC 54 & NovAtel-750 \\ KNDY & iGMAS & CETC-54-GMR-4016 & CETC 54 & GNSS-750 \\ CANB & iGMAS & CETC-54-GMR-4011 & CETC 54 & GNSS-750 \\ DWIN & iGMAS & CETC-54-GMR-4011 & CETC 54 & GNSS-750 \\ KRCH & iGMAS & UNICORE & UB4B0I & UNICORE & NOV750.R4 \\ CNYR & iGMAS & UNICORE & UB4B0I & UNICORE & NOV750.R4 \\ KUN1 & iGMAS & UB4B0-13478 & UNICORE & NOV750.R4 \\ SHA1 & iGMAS & UB4B0-13478 & UNICORE & NOV750.R4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The properties of the selected stations included agency of tracking station, receiver type, manufacturer and antenna type. \begin{table}
\begin{tabular}{l l} \hline \hline
**Items** & **Strategies** \\ \hline Observations & Pseudorange observations \\ Frequency point & BDS-2: B1/B3I; BDS-3: B1/B3I \\ Elevation cutoff & 7.5\({}^{\circ}\)[39; 40] \\ Observation weighting & Elevation weight [sin(elevation)] \\ Satellite orbit & Fixed by broadcast ephemeris \\ Satellite clock offset & Fixed by broadcast ephemeris \\ Topospheric delay & Modified Hopfield for dry and wet parts [41] \\ Ionospheric delay & IF linear combination \\ Receiver antenna & IGS values \\ Relativistic effect & Corrected [42] \\ Earth rotation & Fixed \\ Tide effect & Solid Earth, Pole and Ocean tide [42] \\ Receiver coordinate & Estimated \\ Receiver clock offset & Estimated \\  & Strategy 1: No operation \\ ISB & Strategy 2: Estimated \\ Satellite TGD & Corrected [17; 18; 19] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Single point positioning (SPP) processing strategies. average BMP clock values of BDS-2 and BDS-3 and its differences. Figure 4, we can see that three ACs have different trends in the time series of average BMP clock values, which results from the different reference clocks used by the different ACs. The average BMP clock values of BDS-2 and BDS-3 are not equal, there are differences between BDS-2 and BDS-3, which can indirectly prove that the datum of broadcast clock offsets for BDS-2 and BDS-3 are inconsistent. About the difference between BDS-2 and BDS-3 in time series of average BMP clock values, we can find the multiday stability of GFZ, WHU and SHA are relatively better. From DOY 089 to 123, the daily average of the differences for GFZ, WHU and SHA are around 15.4 ns, 18.8 ns and 5.8 ns, respectively.