## 3 Datasets and Processing Strategies  
To analyze and assess the BDS-2 and BDS-3 broadcast ephemeris in terms of the accuracy of broadcast orbit and clock offsets, the difference of the broadcast clock datum between BDS-2 and BDS-3 and its impact on BDS-2 and BDS-3 combined SPP, the BDS broadcast ephemeris (ftp: //ftp.pecny.cz/LDC/orbits_brd/gop3/) and precise orbit and clock offsets provided by the GFZ (ftp: //ftp.gfz-potsdam.de/GNSS/products/mgex/), WHU ([[ftp://igs.ign.fr/pub/igs/products/mgex/](ftp://igs.ign.fr/pub/igs/products/mgex/)]([ftp://igs.ign.fr/pub/igs/products/mgex/](ftp://igs.ign.fr/pub/igs/products/mgex/))) and SHA ([[http://112.65.161.230/download/index.php](http://112.65.161.230/download/index.php)]([http://112.65.161.230/download/index.php](http://112.65.161.230/download/index.php))) are used to calculate the accuracy of broadcast orbit and clock offsets, orbit-only SISRE and SISRE. Information on the precise products is listed in Table 1.  
Due to the different solution strategies adopted by different ACs in terms of the precise attitude model, the solar radiation pressure model and the strategy of selecting the reference station during the estimation of precise clock offsets [28; 29; 30; 31; 32], the release of BDS-3 satellite precise products is also different. Figure 2 shows the missing of precise products obtained from GFZ, WHU and SHA.  
The 10 IGS multi-GNSS experiment (MGEX) tracking stations [24] and 10 iGMAS tracking stations are selected to assess the BDS SPP performance and research the impact of the inconsistency datum of broadcast clock offsets and the receiver pseudorange bias on BDS-2 and BDS-3 combined SPP. Figure 3 shows the distribution of the selected stations. In order to descript the BDS service performances in these tracking stations, the corresponding mean position dilution of precision (PDOP) is marked in the geographical distribution. Incidentally, the global PDOP grid interval is \(2.5^{\circ}\times 5^{\circ}\), and the cutoff elevation is set to \(7.5^{\circ}\), which is consistent with SPP. All selected tracking stations can receive BDS-2 and BDS-3 observations, and the time interval is 30 s. As with previous studies, the receiver type and the environmental factors (temperature and humidity, etc.) play important roles in the hardware delay [8; 33; 34; 35]. Table 2 shows the properties of the selected stations.  
These selected IGS MGEX and iGMAS tracking stations are used to perform SPP. The least-square method is applied in SPP, the antenna phase center offset (PCO) and phase center variations (PCVs) are corrected by using IGS ANTEX files [36; 37]. About the tropospheric delay, the modified Hopfield model based on the Global Pressure and Temperature 3 (GPT3) model is used to correct the dry and wet tropospheric delay, and the mapping functions of both dry and wet parts are obtained by Vienna  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Agency** & \
\begin{tabular}{c} **Sampling Interval** \\ **of Orbit** \\ \end{tabular} &
\begin{tabular}{c} **Sampling Interval** \\ **of Clock Offsets** \\ \end{tabular} & **Time System** & **Coordinate Frame** \\ \hline GFZ & 5 min & 30 s & GPST & IGS14 \\ WHU & 15 min & 30 s & GPST & IGS14 \\ SHA & 15 min & 300 s & GPST & IGS14 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The properties of BeiDou navigation satellite system (BDS) precise satellite orbit and clock offset products.  
mapping functions 3 (VMF3) according to the elevation angle of each satellite [38]. The ISB processing strategies of not estimating ISB and estimating ISB are performed. Table 3 summarizes the processing strategies for BDS SPP.  
Figure 3: The geographical distribution of the selected stations and the mean position dilution of precision (PDOP) distributions of the corresponding area.  
Figure 2: The missing of BDS-3 precise products obtained from the Helmholtz Centre Potsdam German Research Center for Geosciences (GFZ), Wuhan University (WHU) and Shanghai Astronomical Observatory (SHA) from DOY 089 to 123, 2020.