## 4 Conclusions  
In this study, simulations were conducted on the feasibility of GNSS signals in SSV according to a longitude of geostationary orbit, which is higher than the GNSS satellite orbit, and on a specific region, over Korea and the opposite side. The unusual geometric structure and its effects on GNSS satellite visibility and the UERE should be taken into consideration in order to utilize GNSS signals at a geostationary orbit, in contrast with the general ground environment. Prior to simulation, we investigated the figure of merits of the five components in order to analyze the performance in SSV. Satellite visibility, received power(\(C/N_{0}\)), GDOP, UERE, and navigation error were included. In the simulation results, 7.66 visible satellites on average were secured by utilizing the multi-GNSS at the geostationary orbit using only the main lobe signal, thereby verifying that the minimum number (four) of satellites needed to estimate PNT was ensured. When using additional side lobe signals, it could be seen that more than 25 visible satellites were obtained, which could compute more accurate navigation solution. This study verified that \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Figure** & **Type** & **Main Lobe Signal Only** & **(Main + Side) Lobe Signal** \\ \cline{2-6}  & **GPS** & **Multi** & **GPS** & **Multi** \\ \hline Above Korea & Mean (m) & 1391.02 & 279.80 & 112.79 & 35.88 \\ (128°E) & Std (m) & 382.44 & 439.51 & 76.22 & 7.04 \\ \hline Opposite Korea & Mean (m) & 1046.14 & 93.23 & 112.96 & 23.58 \\ (308°E) & Std (m) & 366.13 & 36.02 & 76.54 & 1.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Navigation error for 24 h in geostationary orbit. Figure 12: Position estimation error for 24 h in geostationary orbit. when utilizing medium orbit satellites, the number of visible satellites in the geostationary orbit at the opposite side of Korea was increased if non-MEO orbit satellite signals were involved in the navigation computation. Accordingly, GDOP was 89.77 for main lobe signals, which was higher than average, and thus positioning accuracy was expected to be significantly degraded. However, using the side lobe signals together, the GDOP could be reduced about 9.94, and these figures affected positioning accuracy. The analysis of the signal reception environment at the geostationary orbit through the link-budget analysis showed that the \(C/N_{0}\) had a mean value of 27.33 dB-Hz, above Korea when using main-lobe and side-lobe signals together. Side lobe signals were distributed near 20 dB-Hz. Thus, using side lobe signals together, the strength of \(C/N_{0}\) would be decreased, although the number of satellites observed would increase. In addition, if it is possible to use GEO and IGSO signals of BDS, the receiver in those areas can receive high power signals all the time, so the received power is slightly higher at the opposite of Korea. Finally, UERE and position estimation errors were computed based on the assumption of static receivers with a high sensitivity capability. The results showed that Multi-GNSS with side lobe signals could obtain more accurate navigation performance than others, significantly. When using only main lobe signal above the Korea, there were intermittent signal outage regions. However, the accuracy of position estimation increased noticeably in areas where additional non-MEO satellite signals could be obtained. It is noted that, in this study, side lobe signals are used to improve the visibility and GDOP. These signals are less affected by the earth blockage effect, which contributes to GDOP enhancement. As a result, it can be seen that position error estimation result is reasonable. Furthermore, as it can be seen from the results which configure the receiver in static mode, it is expected that the utilization of an effective signal processing algorithm and high-performance receiver will be essential to process weak signals in SSV.