## 3 Preliminary Results  
In order to test the basic performance of the new prototype software platform for the five-system ultra-rapid POD, one month's data collected from 130 globally-distributed IGS MGEX stations were used to determine and analyze the ultra-rapid orbit. Figure 2 shows the distribution of the selected tracking stations (the triangles show stations that can observe the four systems (GPS/GLONASS/BDS/Galileo), and the circles show stations that can observe the QZSS). Figure 2 shows that there are 130 stations which can observe four systems. Among them, 67 stations can observe all five systems. Figure 2 also shows that the tracking stations of QZSS have regional distribution. To facilitate the comparison with the MGEX orbit products, we unified the coordinate system to WGS84 and we unified the time system to GPST. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sys**} & \multicolumn{2}{c}{**Frequency**} & \multicolumn{2}{c}{**Signal**} \\ \cline{2-4}  & **Band** & **MHz** & **Phase/Code** \\ \hline \multirow{4}{*}{G} & L1 & 1575.42 & L1C/C1C & L1W/C1W \\ \cline{2-4}  & \multirow{2}{*}{L2} & L2W/C2W & L2X/C2X \\  & & 1227.60 & L2S/C2S & L2L/C2L \\  & & L2C/C2C & L2D/C2D \\ \hline \multirow{4}{*}{\(R_{\text{L}}\)} & G1 & 1598.0625 & \multicolumn{2}{c}{L1C/C1C} \\  & & \(-\)1608.75 & L1P/C1P \\ \cline{2-4}  & \multirow{2}{*}{G2} & 1242.9375 & L2P/C2P \\  & & \(-\)1251.25 & L2C/C2C \\ \hline \multirow{2}{*}{E} & E1 & 1575.42 & L1X/C1X & L1C/C1C \\  & E5a & 1176.45 & L5X/C5X & L5Q/C5Q \\ \hline \multirow{4}{*}{C} & B1 & 1561.098 & \multicolumn{2}{c}{L11/C11} & L2I/C2I \\  & & & \multicolumn{2}{c}{L2X/C2X} \\ \cline{2-4}  & B2 & 1207.14 & L7I/C7I & L7X/C7X \\ \hline \multirow{4}{*}{J} & L1 & 1575.42 & L1C/C1C & L1X/C1X \\ \cline{2-4}  & \multirow{2}{*}{L2} & L2X/C2X & L2L/C2L \\ \cline{1-1} \cline{3-4}  & & & L2S/C2S & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The observation types selected by the new prototype software platform. Sys: System; G: GPS; \(R\): GLONASS (\(k\): the frequency factor); C: BDS; E: Galileo; J: QZSS. Figure 2: Distribution of tracking stations used for ultra-rapid precise orbit determination (triangles: GPS/GLONASS/BDS/Galileo; circles: QZSS). The test period was from 1 January 2018 to 31 January 2018. In this paper, the ultra-rapid orbits of MEO and IGSO satellites were tested. The methods to assess the predicted parts of multi-GNSS ultra-rapid orbits are mainly the analysis of the orbit discontinuities at day boundaries, comparison with IGS/MGEX orbit, and SLR validation, etc. [28; 49; 50]. In this section, we used the first two validation methods, and the assessment steps were carried out as follows:  
1. Five-system ultra-rapid orbits were estimated, and the time latency for estimated ultra-rapid orbits is shown in Figure 3;
2. The six-hour predicted part of each arc were compared to the final MGEX orbit products of GFZ (the accuracy codes are 0 for all satellites in gbm19861.sp3), and the root mean square (RMS) of the position deviation in the radial, along-track, and cross-track directions orbit components was calculated. Figures 11-15 of Appendix A represent the differences between the predicted orbits of five-system ultra-rapid orbits and the orbits of GFZ for GPS, GLONASS, BDS, Galileo, and QZSS satellites. Figures 4-7 represent the root mean square (RMS) of these satellites;
3. The analysis of the orbit discontinuities at day boundaries. Figures 16-17 of Appendix A represent the residuals of the fitting procedure for GPS, GLONASS, BDS, Galileo, and QZSS satellites in the radial, along-track, and cross-track directions orbit components. Figures 8-11 represent the standard deviations (SD) of these satellites. 4.