## 5 Conclusions  
Global service of BDS has been provided since 27 Dec. 2018. At present, eighteen BD3 MEO FOC satellites have been launched into space, transmitting in four open service signals, namely B1I, B1C, B2a and B3I. In the study, we mainly focus on the signal characteristics of the BD3 open service signals. Pseudorange code noise level is estimated by multipath combination and the code bias founded  
Figure 10: The GPS/GLONASS/Galileo/BDS satellites frequency stability calculated by overlapping Allan Deviation. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**PRN**} & \multirow{2}{*}{**Clock**} & \multicolumn{2}{c}{**Interval**} & \multirow{2}{*}{**PRN**} & \multirow{2}{*}{**Clock**} & \multicolumn{2}{c}{**Interval**} \\ \cline{3-4} \cline{6-7}  & & **10,000 s** & & & **86,400 s** & & **10,000 s** & **86,400 s** \\ \hline C01 & RAFS & \(9.46\times 10^{-14}\) & \(8.01\times 10^{-15}\) & C19 & RAFS & \(2.98\times 10^{-14}\) & \(3.28\times 10^{-15}\) \\ C02 & RAFS & \(1.05\times 10^{-13}\) & \(8.82\times 10^{-15}\) & C20 & RAFS & \(2.93\times 10^{-14}\) & \(2.70\times 10^{-15}\) \\ C03 & RAFS & \(9.47\times 10^{-14}\) & \(7.97\times 10^{-15}\) & C21 & RAFS & \(2.84\times 10^{-14}\) & \(2.95\times 10^{-15}\) \\ C04 & RAFS & \(8.45\times 10^{-14}\) & \(7.52\times 10^{-15}\) & C22 & RAFS & \(3.00\times 10^{-14}\) & \(2.98\times 10^{-15}\) \\ C05 & RAFS & \(6.67\times 10^{-14}\) & \(3.24\times 10^{-15}\) & C23 & RAFS & \(1.82\times 10^{-14}\) & \(2.22\times 10^{-15}\) \\ C06 & RAFS & \(9.60\times 10^{-14}\) & \(1.13\times 10^{-14}\) & C24 & RAFS & \(1.99\times 10^{-14}\) & \(2.48\times 10^{-15}\) \\ C07 & RAFS & \(1.06\times 10^{-13}\) & \(9.09\times 10^{-15}\) & C25 & PHM & \(4.24\times 10^{-14}\) & \(5.62\times 10^{-15}\) \\ C08 & RAFS & \(8.25\times 10^{-14}\) & \(1.13\times 10^{-14}\) & C26 & PHM & \(3.39\times 10^{-14}\) & \(4.93\times 10^{-15}\) \\ C09 & RAFS & \(6.83\times 10^{-14}\) & \(6.87\times 10^{-15}\) & C27 & PHM & \(2.30\times 10^{-14}\) & \(2.38\times 10^{-15}\) \\ C10 & RAFS & \(1.05\times 10^{-13}\) & \(1.17\times 10^{-14}\) & C28 & PHM & \(1.91\times 10^{-14}\) & \(1.76\times 10^{-15}\) \\ C11 & RAFS & \(5.72\times 10^{-14}\) & \(6.22\times 10^{-15}\) & C29 & PHM & \(2.46\times 10^{-14}\) & \(2.49\times 10^{-15}\) \\ C12 & RAFS & \(3.68\times 10^{-14}\) & \(4.04\times 10^{-15}\) & C30 & PHM & \(2.46\times 10^{-14}\) & \(2.59\times 10^{-15}\) \\ C13 & RAFS & \(8.73\times 10^{-14}\) & \(1.08\times 10^{-14}\) & C33 & RAFS & \(2.45\times 10^{-14}\) & \(2.41\times 10^{-15}\) \\ C14 & RAFS & \(3.31\times 10^{-14}\) & \(3.94\times 10^{-15}\) & C35 & PHM & \(6.32\times 10^{-13}\) & \(3.84\times 10^{-14}\) \\ C16 & RAFS & \(3.55\times 10^{-14}\) & \(2.64\times 10^{-15}\) & C36 & RAFS & \(7.62\times 10^{-13}\) & \(1.58\times 10^{-14}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The frequency stability of the BD3 satellites at intervals of 10,000 s and 86,400 s.  
in BD2 IGSO and MEO satellites are proven to be eliminated in the BD3 satellites. The multipath combinations show that the B1C pseudorange code is much noisier than the other three signals. In addition, the residuals of pseudorange and phase using four types of IF combinations with about 30-day data are evaluated by precise orbit determination. Fortunately, the pseudorange results are consistent with the multipath combination results. This may be related to the signal constitution and power distribution. The designed minimum received power levels on the ground is \(-159\) dBW for B1C, which is 3 dB lower than that of the BDS B2a signal. According to our analysis, these designs may be the reason for the weak S/N and a slightly noisier signal performance of the B1C signal. The phase combination residuals of these four IF combinations are in the same magnitude and the residuals of B1I-B3I, B1C-B3I, B1I-B2a, B1C-B2a IF phase combinations are 5.9 mm, 5.2 mm, 4.9 mm and 4.8 mm, respectively. Considering the noise amplitude and compatibility with other GNSS, the B1C and B2a combination is recommended in priority.