# Physical Layer Security Based on Non-Orthogonal Communication Technique with Coded FTN Signaling
## 5 Experimental Design and Performance Evaluation
### Performance Evaluation  
Figures 6 and 7 describe the performance of the DVB-S2X system with symbol-wise and block-wise coded FTN signaling schemes, according to the baseband modulation. Figure 6 shows the BER performances of the DVB-S2X systems with 16-QAM. In Figure 6, the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value/Description** \\ \hline LDPC Code Length & 64,800 bits \\ LDPC Code Rate & 2/3 \\ Baseband Modulation & QPSK, 16-QAM \\ Pulse Shape & RRC with 0.35 roll-off factor \\ \(\tau\) Range & 0.5 to 1 (0.05 intervals) \\ Conventional DVB-S2X & Without FTN signaling \\ Eavesdropper Configuration & General FTN receiver with \(\tau=0.75\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters for the experimental design. performance of the symbol-wise coded FTN signaling is about 0.3-0.6 dB better than that of the block-wise coded FTN signaling at BER = \(10^{-5}\). However, in the case of the symbol-wise coded FTN signaling, since the symbol interval should be changed at every symbol time, the implementation complexity becomes high. For the block-wise coded FTN signaling, because the symbol interval is fixed for the block length, a simpler implementation is possible. However, in the case of symbol blocks with a low \(\tau_{\text{blbl}}\) value, high interference causes performance degradation. Therefore, in the case of \(B\) = 10, although the symbol interval can be fixed for ten symbols, the performance is the worst, because of high ISI. In the block-wise coded FTN signaling, since the symbols with low \(\tau\) values can be successively transmitted, the performance degradation value is higher. However, both symbol-wise coded FTN signaling and block-wise coded FTN signaling show smooth operation without serious problems such as error floor, excessive performance degradation, and so on. From the simulation results, it can be shown that the eavesdropper mode cannot demodulate and decode the signal transmitted from the coded FTN signaling system. In Figure 7, the BER performances of QPSK modulation are described. Compared with 16-QAM, the performance degradation of block-wise coded FTN signaling is lower, since the QPSK is more reliable from an ISI standpoint than the 16-QAM. However, the BER performance tendency is similar in that the longer the block length, the worse the BER performance. Figures 8 and 9 depict the BER performance of the variable-length block-wise coded FTN signaling. For a performance comparison, the DVB-S2 system with a general FTN signaling of \(\tau=0.75\) is inserted. Furthermore, the performance of the conventional DVB-S2 without FTN signaling is also added. Figure 8 shows the BER performance of 16-QAM. The performance of general FTN signaling with \(\tau=0.75\) is about 0.7 dB worse than that of the conventional DVB-S2X system at BER = \(10^{-5}\). However, in the ideal case, an efficiency gain of more than 30% can be achieved using FTN signaling with \(\tau\) = 0.75 compared to regular Nyquist signaling. For the coded FTN signaling, compared to regular FTN signaling with \(\tau\) = 0.75, the performance degradation of the symbol-wise coded FTN signaling is about 0.6 dB, while the performance degradation of the variable-length block-wise coded FTN signaling is about 0.4 dB. Since the variable-length block-wise coded FTN signaling adjusts the block length according to the \(\tau\) value, the generation probability of a low \(\tau\) value is lower than that of the symbol-wise coded FTN signaling. In the variable-length block-wise coded FTN signaling, the average \(\tau\) value of the transmission signaling is  
Figure 6: BER performances of symbol-wise coded FTN signaling and block-wise coded FTN signaling in DVB-S2X system with 16-QAM. about 0.785 (i.e., \(\mathrm{E}[\tau]=0.785\)). Therefore, by using variable-length block-wise coded FTN signaling, the performance of the coded FTN signaling is improved. Figure 9 shows the BER performances of the QPSK modulation.