# Effects of Equatorial Plasma Bubbles on Multi-GNSS Signals: A Case Study over South China
## 4 Signal Quality Assessment  
The above results indicate that EPB could induce greater S\({}_{4}\) values and TEC oscillations, and in this section, the influences of EPB on GNSS signal quality are analyzed quantitatively. Note that the second and third generation BDS are both in operation, and the constellation design for BDS consists of satellites in three different orbits, geostationary orbit (GEO), inclined geosynchronous orbit (IGSO) and Medium Earth orbits (MEOs). The signal quality for BDS is further assessed according to different generations and satellite orbits in this section. Tables 1 and 2 show the detailed information of the satellite lists for BDS-2 and BDS-3, respectively. Figure 3: Comparison of the S\({}_{4}\) index (BDS: L2I, SBAS: L1C), airglow depletion, and deviation VTEC (BDS: L2I-L6I, SBAS: L1C-L5I) for eight GEO satellites during 12–20 UT on 3 April 2022. (**a**) Geographical distribution of ground-based station (red triangle) and IPVS (black pentagrams) for eight GEO satellites. From top to bottom (**b–i**) are eight GEO satellites distributed from west to east. Figure 4 shows several parameters for the BDS-C03 GEO satellite at B3 frequency band (1268.52 MHz, C6I, L6I, and S6I). Figure 4a,b show the S\({}_{4}\) index, airglow depletion, and dVTEC, and Figure 4c-e show the carrier-to-noise ratio (C/N0), cycle slip, and loss of lock. Here, the numbers of CSs and LoLs are classified in 5 min intervals. Apparently, there was a large fluctuation in the signal as it passed through the EPB. The signal strength decreased significantly, and many cycle slips and losses of lock events occurred. At the center of the EPB, the signal experiences more cycle slips and loss of locks. \begin{table}
\begin{tabular}{c c c c} \hline
**PRN** & **Satellite Name** & **Longitude (\({}^{\circ}\)E)** & **Lauch Date** \\ \hline C59 & BDS-3 GEO1 & 140 & 1 November 2018 \\ C60 & BDS-3 GEO2 & 80 & 9 March 2020 \\ C38 & BDS-3 IGSO1 & 119 & 20 April 2019 \\ C39 & BDS-3 IGSO2 & 118.5 & 24 June 2019 \\ C40 & BDS-3 IGSO3 & 119.5 & 5 November 2019 \\ C19 & BDS-3 MEO1 & - & 5 November 2017 \\ C28 & BDS-3 MEO8 & - & 11 January 2018 \\ C21 & BDS-3 MEO3 & - & 12 February 2018 \\ C22 & BDS-3 MEO4 & - & 12 February 2018 \\ C29 & BDS-3 MEO9 & - & 29 March 2018 \\ C23 & BDS-3 MEO5 & - & 29 July 2018 \\ C24 & BDS-3 MEO6 & - & 29 July 2018 \\ C26 & BDS-3 MEO11 & - & 24 August 2018 \\ C25 & BDS-3 MEO12 & - & 24 August 2018 \\ C33 & BDS-3 MEO14 & - & 19 September 2018 \\ C35 & BDS-3 MEO15 & - & 15 October 2018 \\ C34 & BDS-3 MEO16 & - & 15 October 2018 \\ C45 & BDS-3 MEO23 & - & 23 September 2019 \\ C43 & BDS-3 MEO21 & - & 23 November 2019 \\ C44 & BDS-3 MEO22 & - & 23 November 2019 \\ C41 & BDS-3 MEO19 & - & 16 December 2019 \\ C42 & BDS-3 MEO20 & - & 16 December 2019 \\ \hline \end{tabular}
\end{table} 
Table 2: List of the BDS-3 satellites used in this study. The longitudes of the sub-satellite points for GEO satellites and the longitudes of the intersection of sub-satellite trajectories for IGSO satellites are shown in the third column. \begin{table}
\begin{tabular}{c c c c} \hline
**PRN** & **Satellite Name** & **Longitude (\({}^{\circ}\)E)** & **Lauch Date** \\ \hline C04 & BDS-2 GEO4 & 160 & 31 October 2010 \\ C05 & BDS-2 GEO5 & 59 & 24 February 2012 \\ C02 & BDS-2 GEO6 & 84 & 25 October 2012 \\ C03 & BDS-2 GEO7 & 110.5 & 12 June 2016 \\ C01 & BDS-2 GEO8 & 144.5 & 17 May 2019 \\ C06 & BDS-2 IGSO1 & 105.5 & 31 July 2010 \\ C07 & BDS-2 IGSO2 & 106.5 & 17 December 2010 \\ C08 & BDS-2 IGSO3 & 105 & 9 April 2011 \\ C09 & BDS-2 IGSO4 & 95.9 & 26 July 2011 \\ C10 & BDS-2 IGSO5 & 94 & 1 December 2011 \\ C13 & BDS-2 IGSO6 & 96 & 11 October 2016 \\ C16 & BDS-2 IGSO7 & 113.5 & 9 July 2018 \\ C11 & BDS-2 MEO3 & - & 29 April 2012 \\ C12 & BDS-2 MEO4 & - & 29 April 2012 \\ C14 & BDS-2 MEO6 & - & 18 September 2012 \\ \hline \end{tabular}
\end{table} 
Table 1: List of the BDS-2 satellites used in this study.