## 4 Simulation Results  
In this section, we verify the simulation results and the theoretical performance of the proposed CIM-GSDM system in terms of Bob and Eve. Moreover, the comparison between the original CIM-SDM system and the proposed CIM-GSDM system is exhibited as well under the same spectral efficiency. More specifically, theoretical and simulated BER performance at both Bob and Eve is obtained and compared in details. In the process of simulations, assume that Alice is equipped with \(N_{t}=8\) antennas and the distance between each antennas is \(d=\lambda/4\). The signals are transmitted over free space channels. Considering Eve desires eavesdropping, it is assumed that the receivers at Eve are close to the [PERSON]'s ones due to the characteristic of direction modulation. The interference matrixand the number of receivers at Bob and Eve are different in simulations. The assumptions are the same as theoretical analysis. More details about simulations are shown in Table 1 as follows. As shown in Figure 3, [PERSON]'s and [PERSON]'s BER performances of proposed CIM-GSDM scheme employing \(N_{t}=8\), \(N_{r}=6\), \(N_{e}=6\) and QPSK are compared. The interference matrix is \(\Lambda=diag\{e^{\Theta\Lambda}\}(\Theta_{\Lambda}=\{28^{\circ},32^{\circ},45^{ \circ},55^{\circ},60^{\circ},65^{\circ}\})\). Observed in Figure 3, the theoretical curves of Bob both approximate well to the simulated curves at high signal noise radio (SNR). The BER performance of Bob are significantly better than that of [PERSON] with the employment of the proposed CIM-GSDM system at both middle and high SNR even if the receivers at Eve are located near to [PERSON]'s. The theoretical and simulation results perform better in high SNR region since the interference caused by noise relatively decreases with SNR increasing. More explicitly, it implies that the proposed CIM-GSDM system causes interference to Eve while achieves transmission to [PERSON], which develop the security of transmission as a benefit of employing the proposed CIM-GSDM scheme. Figure 4 suggests [PERSON]'s and [PERSON]'s BER performances of proposed CIM-GSDM scheme in comparison to the traditional CIM-SDM counterparts employing \(N_{t}=8\), \(N_{r}=6\), \(N_{e}=6\) \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Figure** & **Scheme** & \(N_{t}\) & \(N_{r}\) & \(N_{u}\) & \(\Theta B\) & \(N_{e}\) & \(\Theta E\) & \(M\) \\ \hline Figure 3 & CIM-GSDM & 8 & 6 & 2 & \(\begin{array}{c}\{15^{\circ},60^{\circ},120^{\circ},\\ 160^{\circ},215^{\circ},285^{\circ}\}\end{array}\) & 6 & \(\begin{array}{c}\{30^{\circ},75^{\circ},135^{\circ},\\ 175^{\circ},230^{\circ},300^{\circ}\}\end{array}\) & 4 \\ \hline Figure 4 & CIM-GSDM & 8 & 8 & 2 & \(\begin{array}{c}\{15^{\circ},55^{\circ},90^{\circ},130^{\circ},\\ 170^{\circ},210^{\circ},250^{\circ},290^{\circ}\}\end{array}\) & 8 & \(\begin{array}{c}\{30^{\circ},70^{\circ},105^{\circ},145^{\circ},\\ 185^{\circ},235^{\circ},265^{\circ},305^{\circ}\}\end{array}\) & 4 \\ \hline Figure 5 & CIM-GSDM CIM-SDM & 8 & 6 & 2 & \(\begin{array}{c}\{15^{\circ},60^{\circ},120^{\circ},\\ 160^{\circ},215^{\circ},285^{\circ}\}\end{array}\) & 6 & \(\begin{array}{c}\{30^{\circ},75^{\circ},135^{\circ},\\ 175^{\circ},230^{\circ},300^{\circ}\}\end{array}\) & 4 \\ \hline Figure 6 & CIM-GSDM CIM-SDM & 8 & 8 & 2 & \(\begin{array}{c}\{15^{\circ},55^{\circ},90^{\circ},130^{\circ},\\ 170^{\circ},210^{\circ},250^{\circ},290^{\circ}\}\end{array}\) & 8 & \(\begin{array}{c}\{30^{\circ},70^{\circ},105^{\circ},145^{\circ},\\ 185^{\circ},235^{\circ},265^{\circ},305^{\circ}\}\end{array}\) & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of simulations. Figure 3: [PERSON]’s and [PERSON]’s BER performances of proposed CIM-GSDM scheme employing \(N_{t}=8\), \(N_{r}=6\), \(N_{e}=6\) and QPSK. and QPSK at the same spectral efficiency. Specifically, the BER performance of [PERSON] suffers great interference at both the CIM-SDM and CIM-GSDM scheme, which implies these two scheme can improve the security as it needs.