# A Comprehensive Evaluation of Possible RNSS Signals in the S-Band for the KPS
## 4 FoMs Analysis
### SSC Analysis Results  
For RF compatibility analysis in the S-band, we considered existing RNSS and MSS systems (i.e., NavIC and Globalstar). RF compatibility between the candidate signals and the existing signals was evaluated using the SSC. Even when the modulation scheme is the same, the SSC can vary with the front-end bandwidth of the receiver. The front-end bandwidth of the receiver is determined by the receiver's uses. Receivers for precise positioning use, such as geodetic surveys, have a wide bandwidth. However, low-cost receivers, such as RNSS receivers embedded in smartphones, have a narrow bandwidth to reduce the implementation cost and front-end size. Therefore, we analyzed the SSC, assuming a front-end bandwidth of 16.5 MHz or the same as the main lobe width of the candidate signal. In the latter case, the front-end bandwidth is defined as \(2f_{c}\) for BPSK signals and \(2(f_{s}+f_{c})\) for BOC signals. Table 4 enumerates the SSC between the candidate signals and the existing signals in the S-band. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Center** & **Modulation** & **Chip Rate\(f_{c}\)** & \begin{tabular}{c} **Subcarrier** \\ **Frequency** \\ **(MHz)** \\ \end{tabular} & **Remarks** \\ \hline \multirow{8}{*}{\begin{tabular}{c} 2492.028 \\ (BOC\({}_{\text{s}}\)) \\ \end{tabular} } & 1.023 & - & NavIC S-SPS \\  & & 1.023 & - & [22] \\  & BPSK-R & 4.092 & - & [22] \\  & & 5.115 & - & - \\  & & 8.184 & - & [22] \\ \hline \multirow{8}{*}{\
\begin{tabular}{c} 2492.028 \\ \end{tabular} } & 1.023 & 1.023 & [22] \\  & & 1.023 & 2.046 & - \\  & & 2.046 & 2.046 & - \\  & & 1.023 & 3.069 & - \\  & & 2.046 & 3.069 & - \\  & & 3.069 & 3.069 & - \\  & & 4.192 & 4.192 & [23] \\  & & 2.046 & 5.115 & NavIC S-RS \\ \hline \multirow{8}{*}{
\begin{tabular}{c} Cosine-BOC \\ (BOC\({}_{\text{c}}\)) \\ \end{tabular} } & 1.023 & 1.023 & - \\  & 1.023 & 2.046 & - \\ \cline{1-1}  & 2.046 & 2.046 & - \\ \cline{1-1}  & 1.023 & 3.069 & - \\ \cline{1-1}  & & 2.046 & 3.069 & - \\ \cline{1-1}  & & 3.069 & 3.069 & - \\ \cline{1-1}  & & 4.192 & 4.192 & - \\ \hline \multirow{2}{*}{MBOC} & 1.023 & 1.023 & \multirow{2}{*}{[22]} \\ \cline{1-1}  & & & 6.138 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Center frequency and modulation methods for each candidate. Since the NavIC SPS signal has a narrow main lobe, it has a low SSC for BOC signals. BOC\({}_{\rm c}\)(4,4) had the lowest SSCs with the NavIC SPS signal as \(-\)85.97 for both front-end bandwidths. If the chip rate and subcarrier frequency are the same, the cosine-BOC signal has a lower SSC than the sine-BOC signal. This is because the shape of the PSD of the cosine-phased BOC has smaller sidelobes between the two main lobes than sine-phase BOC. This characteristic was considered in the case of changing the Galileo E6 Public Regulated Service (PRS) signal from BOC\({}_{\rm s}\)(10,5) to BOC\({}_{\rm c}\)(10,5) to increase the spectral separation with the E6 Commercial Service (CS) signal. The SSC between the candidates and NavIC RS signal is considerably different according to the receiver's front-end bandwidth. When the front-end bandwidth is 16.5 MHz, the SSC of BOC\({}_{\rm s}\)(3,1) was the lowest among the candidates at \(-\)80.34. However, when the front-end bandwidth was equal to the candidate's main lobe width, BOC\({}_{\rm c}\)(1,1) had the lowest SSC at \(-\)84.27. As shown in Figure 2, this was because the spectral overlap region between the side lobe of BOC\({}_{\rm c}\)(1,1) and the main lobes of the NavIC RS signal was not considered in the SSC calculation when the receiver bandwidth was limited as the main lobe width of the candidate. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Candidates**} & \multirow{2}{*}{ \begin{tabular}{c} **B\({}_{r}\)** \\ **(MHz)** \\ \end{tabular}