## 4 Numerical Results and Discussions
Additionally, at a considerably high value of \(\gamma\), the error performance becomes insulated from any variation in \(\rho\)._  
Figure 6 demonstrates the effect of an absent and active jammer. We can notice that an always-on jammer has a more adverse influence on the system's performance than Gaussian noise. At \(\gamma\) = 20 dB, for \(N\) = 2, the ABER increases from \(5.627\times 10^{-3}\) to \(1.667\times 10^{-2}\) as \(\rho\) increases from 0 to 1. Moreover as the \(\gamma\) increases, the difference in the toll the two noises take on the performance widens. When two transmit apertures are employed, for \(\rho\) = 0 and 1, the bit error rate has a difference of \(2.094\times 10^{-2}\) and \(1.874\times 10^{-3}\) at \(\gamma\) = 15 dB and 30 dB, respectively. It is also observed that this divergence inflates as \(N\) increases. At \(\gamma\) = 25 dB, the gap between the bit error contributed by the jammer and the Gaussian noise is \(4.931\times 10^{-3}\) and \(6.468\times 10^{-4}\) for \(N\) = 2 and 3, respectively. Hence, the transmit aperture selection technique performs substantially better in the absence of a jammer. In Figure 7, we plot the ABER values of the FSO system with \(N\) equal to 2 and 3, while varying the PE severity faced by the jammer. It can be observed from the figure that as the value of \(\xi_{j}\) increases, the PE suffered by the jammer reduces, and thus it disrupts the regular communication more strongly. It can be noticed from the figure that for ABER = \(10^{-2}\), as the PE parameter changes from 0.5708 to 1.7196, \(\gamma\) has to be increased by 10 dB for the FSO system with two transmit apertures. However, under the same conditions, if the number of transmit apertures is increased to three, then only 7.5 dB of additional SJR is required to attain ABER = \(10^{-2}\). This also proves that PE conditions are more relenting when \(N\) increases. Figure 5: ABER versus SJNR (dB) curves for FSO system with \(N\) = 2, with varying degree of jammer’s activity. **Remark 5**. : _The preceding discussion proves that serious PE conditions in the jamming link improve the ABER of the FSO system. Moreover, the bit error performance enhances as \(N\) increases for an arbitrary value of \(\zeta_{j}\)._  
In Figure 8, we present the comparison of different existing techniques with the transmit aperture selection technique in their resilience to combat the jamming noise. We plot the simulations of the OSSK scheme and RC scheme employed in a \(2\times 1\) FSO system under attack from a jammer. The channel is modeled for saturated AT and PE conditions for all the schemes. The PE parameters for an authorized transmitter and jammer are taken to be 1.5285 and 0.5708. It is clear from the plot that the transmit aperture selection technique outperforms RC and OSSK significantly. At \(\gamma\) = 20 dB, the error rates for OSSK, RC, and aperture selection are 0.0312, 0.0139, and 0.0082, respectively. The RC and aperture selection have a 3 dB gap between them, with the same diversity order of 1, whereas OSSK has a diversity order of 0.5, and hence the gap widens as \(\gamma\) increases. Figure 6: ABER versus SJNR (dB) curves for the FSO systems having \(N\) = 2 and 3 in the presence and absence of the jammer. Figure 7: ABER versus SJNR (dB) curves for FSO systems having \(N\) = 2 and 3 with varying PE severity in presence of jammer (\(\rho=1\)). Numerical Studies over Gamma-Gamma FadingNow, we study the impact of aperture selection on an FSO system when the channel is modeled by GG statistics, augmented with PE. The calculations carried out in the previous section are extended for GG fading to scrutinize the defined system for various AT regimes. As it is a very grueling task to analyze an FSO system employing a transmit aperture selection technique to counter a jammer, we provide the simulation results in conformity with the numerical results obtained in the previous sections.