# Characterization of GNSS Signals Tracked by the iGMAS Network Considering Recent BDS-3 Satellites
## 2 Datasets  
For BDS-3 satellites, signal design has been upgraded compared with BDS-2. In addition to the old B1I and B3I signals inherited from the BDS-2 satellites, several new open service signals are also transmitted by the BDS-3 satellites, namely, B1C at 1575.42 MHz, B2a at 1176.45 MHz, and B2b at 1207.14 MHz [12]. The B1C signal is compatible with GPS L1 and Galileo E1 signals; the B2a signal shares the same frequency as GPS L5 and Galileo E5a signals; and the B2b signal matches with the Galileo E5b signal. In addition, the BDS-3 B2b signal shares the same frequency as the BDS-2 B2 signal, but with a different modulation type. The frequencies, wavelengths and chip rates of BDS-2 and BDS-3 open service signals are listed in Table 2.  
The iGMAS tracking network was developed by the China Satellite Navigation Office to track multi-GNSS observations and provide satellite orbits and clocks, station coordinates and many other kinds of information for users. At the time of this study, the iGMAS network consisted of 23 stations, 17 of which can track multi-GNSS satellites, including the recently deployed BDS-3 satellites. The distribution of these 17 stations is shown in Figure 1. Table 3 lists the configuration of these stations, which includes three different types of receivers and four different types of antennas. All receivers can simultaneously track GPS L1/L2/L5, Galileo E1/E5a/E5b, BDS-2 B1I/B3I, and BDS-3 B1I/B1C/B2a/B3I signals, and the GNSS_GGR receiver can additionally track BDS-3 B2b signals. Ten-day observation data collected by these stations from 28 May 2018 (DOY 148) to 6 June 2018 (DOY 157) are used for this study.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Satellite** & **SVN** & **Int. Sat. ID** & **Manuf.** & **PRN** & **Notes** \\ \hline BDS-3 MEO-1 & C201 & 2017-069A & CAST & C19 & Slot B-7; launched 5 Nov. 2017 \\ BDS-3 MEO-2 & C202 & 2017-069B & CAST & C20 & Slot B-8; launched 5 Nov. 2017 \\ BDS-3 MEO-3 & C206 & 2018-018B & CAST & C21 & Slot B-5; launched 12 Feb. 2018 \\ BDS-3 MEO-4 & C205 & 2018-018A & CAST & C22 & Slot B-6; launched 12 Feb. 2018 \\ BDS-3 MEO-7 & C203 & 2018-003A & CAS & C27 & Slot A-4; launched 11 Jan. 2018 \\ BDS-3 MEO-8 & C204 & 2018-003B & CAS & C28 & Slot A-5; launched 11 Jan. 2018 \\ BDS-3 MEO-9 & C207 & 2018-029A & CAS & C29 & Slot A-2; launched 29 Mar. 2018 \\ BDS-3 MEO-10 & C208 & 2018-029B & CAS & C30 & Slot A-3; launched 29 Mar. 2018 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Status of the BDS-3 satellites (June 2018).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**System** & **Signal** & **Frequency (MHz)** & **Wavelength (cm)** & **Chip Rate (Mcps)** \\ \hline \multirow{3}{*}{BDS-2} & B1I & 1561.098 & 19.20 & 2.046 \\  & B2I & 1207.140 & 24.83 & 2.046 \\  & B3I & 1268.520 & 23.63 & 10.23 \\ \hline \multirow{3}{*}{BDS-3} & B1I & 1561.098 & 19.20 & 2.046 \\  & B1C & 1575.420 & 19.03 & 1.023 \\ \cline{1-1}  & B2a & 1176.450 & 25.48 & 10.23 \\ \cline{1-1}  & B2b & 1207.140 & 24.83 & 10.23 \\ \cline{1-1}  & B3I & 1268.520 & 23.63 & 10.23 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Open service signals of BDS-2 and BDS-3.