## 3 Results
### Rnss + Four-Gnss  
At present, three QZO satellites and one GEO satellite make up QZSS, and these satellites transmit signals to provide services [40]. Three QZSS satellites, which will be deployed in the future, include one QZO satellite and two GEO satellites, one of which has a small inclination angle and is called a quasi-geostationary Earth orbit (QGEO) satellite [41]. Figure 10: Satellite visibility and GDOP of the four-GNSS-NG+LEO-mix satellites and their improvement rate: (**a**) visible satellites of four-GNSS-NG+LEO-mixed; (**b**) visible satellites improvement rate of the four-GNSS-NG+LEO-mix compared to that of the four-GNSS-NG; (**c**) GDOP of the four-GNSS-NG+LEO-mix; (**d**) GDOP improvement rate of the our-GNSS-NG+LEO-mix compared to that of the four-GNSS-NG. The 7-QZSS satellite constellation parameters are listed in Table 6. Their ground tracks are plotted in Figure 11a. For the NavIC (formerly known as IRNSS), seven satellites--4 in geosynchronous and 3 in geostationary orbits, are on-orbit operations [42; 43]. In the future, five new visible satellites (NVS) will be added to the constellation, in which NVS-01 (also known as IRNSS-I)) will replace IRNSS-1G, while the other satellite (NVS-02-NVS-05) parameters are summarized in Table 6[43]. The ground tracks of the 11-NavIC satellites are shown in Figure 11b. The method discussed earlier was used to assess the QZSS satellite visibility. The results are presented in Figure 12a,b, and Table 7 (to simplify the calculation, the QGEO satellite is regarded as a GEO satellite). One can see that the QZSS service is roughly in the Asia-Pacific region. More than two satellites can be observed for 4-QZSS in (60\({}^{\circ}\)E-180\({}^{\circ}\)E, 60\({}^{\circ}\)S-60\({}^{\circ}\)N), while 7-QZSS exceeds four. Specifically, in Southeast Asia and in Northwestern Australia, five visible satellites can be guaranteed. However, QZSS satellites are rarely observed at low altitudes in the Western Hemisphere. Similar to the QZSS, there are almost no visible NavIC satellites in most areas of North and South America. For 7-NavIC, four or more visible satellites are present in (30\({}^{\circ}\)E-150\({}^{\circ}\)E, 60\({}^{\circ}\)S-60\({}^{\circ}\)N) while the number of 11-NavIC satellites reaches six. Specifically, with full 11-NavIC constellations, at least 10 satellites are always visible from the whole India as well as its surrounding areas. Generally, the visibility of 7-QZSS satellites (average: 5.57) increases by 0.9-3 (average: 2.17) in the areas of (60\({}^{\circ}\)E-180\({}^{\circ}\)E, 60\({}^{\circ}\)S-60\({}^{\circ}\)N) compared to 4-QZSS satellites, and the value for 11-NavIC satellites (average: 8.78) with 7-NavIC is 1.83-4 (average: 3.11) in the areas of (30\({}^{\circ}\)E-150\({}^{\circ}\)E, 60\({}^{\circ}\)S-60\({}^{\circ}\)N). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**System** & \multicolumn{3}{c}{**QZSS**} & \multicolumn{3}{c}{**NavIC**} \\ \hline Orbit Type & GEO & QGEO & QZO & GEO & IGSO \\ Satellite Number & 2 & 1 & 4 & 3 & 8 \\ Angle of Inclination & 0\({}^{\circ}\) & \(>\)1\({}^{\circ}\) & 41\({}^{\circ}\) & 0\({}^{\circ}\) & 29\({}^{\circ}\) & 42\({}^{\circ}\) \\ Altitude (km) & & 35,786 & & & 35,786 & \\ Center of Longitude & 90\({}^{\circ}\)E/127.5\({}^{\circ}\)E & 185\({}^{\circ}\)E & 139\({}^{\circ}\)E/148\({}^{\circ}\)E & 34\({}^{\circ}\)E/83\({}^{\circ}\)E/131.5\({}^{\circ}\)E & 55\({}^{\circ}\)E/111.75\({}^{\circ}\)E \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Constellation parameters of QZSS and NavIC. Figure 11: (a) ground tracks of 7-QZSS; (b) ground tracks of 11-NavIC. To evaluate the contribution of QZSS and NavIC for regional services, the estimated number of the four-GNSS-NG+7-QZSS and four-GNSS-NG+11-NavIC visible satellites as well as their combination GDOP positioning were calculated. As shown in Figure 13 and Table 7, with a 5\({}^{\circ}\) mask, there are more than 37 four-GNSS-NG+7-QZSS satellites (average: 50.94) in the Eastern Hemisphere.