## 5 Conclusions and Prospects  
In this study, the BDS-3 experimental satellite's precise orbit determination and the corresponding analyses of the results were conducted based on the iGMAS and MGEX networks. In the data processing, an improved cycle-slip detection and repair algorithm was proposed to overcome the disadvantages of the traditional Turboedit in the iGMAS data. From the analysis of observations, it is suggested that the new algorithm is reliable and efficient in improving the data availability of iGMAS observations and accuracy of the parameters related to BDS-3, which considers the correlation of ionospheric delays between adjacent epochs based on the polynomial prediction. Moreover, the improved algorithm preprocesses observations epoch-wise and can optimize the observations in real-time. The insufficient BDS-3 observations caused by the tracking stations were the major factor for limiting its orbit accuracy. In this study, the MGEX observations were used to enhance the estimation of the iGMAS station-related parameters, which indirectly improved the accuracy of the BDS-3 orbit parameters. However, the observation types from the iGMAS for BDS-3 were B1 and B3, while MGEX mainly tracked B1 and B2 for BDS-2. Therefore, this study designed two BDS-3 orbit determination methods, namely, NES and SS, to achieve the combination of different observations. In NES, the common parameters were obtained through the Gaussian elimination method based on the normal equation from the BDS-3 orbit determination with iGMAS, and that of GPS and BDS-2 orbit determination with iGMAS and MGEX. However, SS was utilized to fix the iGMAS station-related parameters by the PPP network solution with GPS and BDS-2 observations. Then, the fixed parameters were assumed as the known parts in the BDS-3 orbit determination. Moreover, a matrix decomposition method was proposed in this study to improve the efficiency of the parameter estimation in NES. One-year BDS-3 (C31, C32, C33, and C34) orbit determination based on the MGEX and iGMAS observations were conducted, and the corresponding orbit accuracy of four satellites were analyzed. The accuracy of BDS-3 was calculated from the discrepancy of the overlapping arcs and SLR residuals. Results showed that BDS-3 orbit accuracy obtained through the NES and SS were 31.0, 36.0, 40.3, and 50.1 cm and 34.6, 39.4, 43.4, and 55.5 cm, respectively. Meanwhile, the RMS of the SLR residuals \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Scheme 1** & \multicolumn{2}{c}{**Scheme 2**} & \multicolumn{2}{c}{**Scheme 3**} & \multicolumn{2}{c}{**Scheme 4**} \\ \hline
**Satellites** & **3D RMS** & **3D RMS** & **Improvement** & **3D RMS** & **Improvement** & **3D RMS** & **Improvement** \\ \hline C31 & 45.2 & 42.1 & 6.86\% & 30.2 & 33.19\% & 29.8 & 34.07\% \\ C32 & 53.1 & 49.5 & 6.79\% & 34.1 & 35.78\% & 31.3 & 41.05\% \\ C33 & 137.5 & 134.2 & 2.40\% & 41.6 & 69.74\% & 38.1 & 72.29\% \\ C34 & 174.1 & 149.0 & 14.42\% & 53.1 & 69.50\% & 44.7 & 74.33\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Orbit 3D RMS (cm) of different schemes and its improvement. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Satellites** & **Turboedit (Scheme 1)** & **Improved Algorithm (Scheme 2)** \\ \hline C31 & 22.14\% & 8.48\% \\ C32 & 19.32\% & 6.42\% \\ C33 & 43.10\% & 24.49\% \\ C34 & 38.96\% & 18.50\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The percentage of eliminated data based on BDS-3 orbit determination. were 55.1, 49.6, 61.5, and 70.9 cm and 60.5, 53.6, 65.8, and 73.9 cm, respectively. The accuracy of the BDS-3 orbit was gradually improved by fitting the trend of overlapping arcs, which was mainly related to the increased number of BDS-3 stations in the iGMAS network. In addition, it was found that the orbit accuracy was highly-correlated with the \(\beta\) angle, especially for IGSO (C31 and C32), during the experimental period.