## 5 Performance Evaluation for C Band Signals  
### PSD of C Band Signals  
The ITU clearly stipulates that the future C band signals can't interfere with the normal radio astronomy services (RA, 4990-5000 MHz) and microwave landing system (MLS, 5030-5150 MHz) [4,13]. To meet the strict compatibility condition constraints of the C band, the PSD of modulated signals should have the following characteristics: (1) the majority of power should be concentrated into the main lobe; (2) a  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Merit Factors** & **B_M_2 RC(8)** & **BOCs(4,4)** & **BOCc(4,4)** & **BPSK(8)** & **MSK-BOC(4,4)** \\ \hline \(Q_{\textit{CTANS}}\) & 70.2910 & 70.7160 & 71.0772 & 72.8167 & 70.5057 \\ \(Q_{\textit{CTANW}}\) &  
stronger spectrum roll-off in side lobes should be provided in order to significantly cut down spectrum leakage or interference to RA and MLS.  
To make a fair analysis, this paper compares BPSK(10), a Galileo C band candidate (MSK(10)) [13] and Q_M_2 RC(10) with similar spectral occupancy within the 20 MHz bandwidth of the C band. The normalized PSD of such signals are shown in Figure 6.  
It is shown that the proposed Q_M_2 RC(10) can centralize most of power into the main lobe while effectively inhibiting the re-growth of spectrum side lobes compared to other competitors. In view of the stringent compatibility requirements for RA and MLS, without strong output filtering, it is impossible to limit the emissions for any signal to the level required for RA and MLS [4]. Thus, from the C band signal design point of view, the main factor to be addressed is to limit the out-of-band (OOB) emission power based on the fact that a signal with relatively low OOB emission power could significantly mitigate signal distortion caused by non-ideal filter characteristics and degrade noise level to meet strict RA and MLS constraints while also contributing to reducing design complexity and cost of filters on satellites. Table 3 assesses and compares the out-of-band loss within the 20 MHz bandwidth for C band navigation and the OOB emission power of proposed C band candidate signals at RA and MLS services, where a quantity called out-of-band loss is defined as:  
\[\lambda_{{}_{loss}}=\left|10\times\log_{10}\left(\int_{-B/2}^{B/2}G_{s}(f)df \right)\right| \tag{31}\]  
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Signal**} & **OOB Emission Power in** & **OOB Emission Power in 5030-5150 MHz** & **Out-of-Band Loss in 5010-5030 MHz for** \\  & **4990–5000 MHz band (RA) (dBc)** & **Band (MLS) (dBc)** & **C Band Navigation (dB)** \\ \hline Q_M_2 RC(10) & –49.9821 & –20.4880 & 0.0783 \\ BPSK(10) & –20.8451 & –13.5014 & 0.4428 \\ MSK(10) & –29.9547 & –17.6705 & 0.1512 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The OOB emission power and out-of-band loss of modulation candidates in the C band.  
Figure 6: PSD of modulation candidates in C band.  
As shown in Table 3, the out-of-band losses for the Q_M_2 RC(10) signal within the 20 MHz bandwidth are separately 0.3645 dB and 0.0729 dB lower with respect to BPSK(10) and MSK(10). Besides, the OOB emission power of Q_M_2 RC(10) in the RA and MLS band are -49.9821 dBc and -20.4880 dBc, which are even 20.0274 dBc and 2.8175 dBc lower than those of the MSK signal. Due to the high spectral efficiency and relatively low OOB emission power of the Q_M_2 RC signal, the spectral separation of C band signals with RA and MLS services can be improved significantly.