## 1 Introduction
[21] focused on an FSO system in a maritime environment and conducted experimental analysis of its performance. The AT is tackled using adaptive optics in [22]. In [23; 24], a selection combining technique has been used to improve the quality of FSO links. A switching scheme to toggle between radio frequency (RF) and the FSO system has been proposed for hybrid a RF-FSO system in [25]. However, the effect of PE and jammers has not been studied in these works. In [26], a multiple-input single-output (MISO) FSO system is studied in the presence of an eavesdropper, and the secrecy rate is calculated. However, AT is not taken into consideration here. In [27], an FSO system with a jammer was studied for optical space shift keying (OSSK). Ref. [28] presented the application of the fault location method based on a deep neural evolution network to improve the accuracy of fault location in cloud data center interconnection. While it is a novel idea, it increases the hardware challenge in complexity and cost manifold. This work favors the transmit aperture selection technique due to its low implementation complexity and prowess in evaluating errors while simultaneously reducing power requirements. In [29], the authors addressed the issue of signal crosstalk and fragmentation of spectrum during resource allocation. Since the transmit aperture selection technique employs only one transmit aperture to disseminate the user information, the problems of crosstalk and spectral fragmentation diminish inordinately in contrast to a MISO system. Nonetheless, the transmit aperture selection technique has not been studied so far for an FSO system under the attack of a jammer. The discussion above motivates us to study an \(N\times 1\) MISO-FSO system in outdoor atmospheric surroundings, under the jammer's attack, by analyzing its bit error rate (BER) performance and studying its asymptotic behavior. The novelty of this work is as follows:  
* The jamming signal is not considered to be Gaussian noise; instead, an inclusive study is carried out where additive Gaussian noise and noise from a jamming signal due to random AT are considered. We consider a random jammer that becomes active with a probability of \(\rho\) during a particular instance of time and stays silent for the rest of the time frame with probability \(1-\rho\). Thus, the study includes partial-band and broadband jamming. * We derive an analytical expression of probability distribution function (PDF) of a maximum of \(N\) channel fading coefficients that follow the negative exponential model for saturated AT with PE. * We calculate the PDF of the received signal at the receiver of an MISO-FSO system employing transmit aperture selection. Based on the derived expression, a closed-form expression of BER is calculated. * A comparative study is made for different degrees of severity of PE and activity of the random jammer. * The coding gain and diversity order are calculated to examine the system's asymptotic behavior under the influence of both noises. * We also examine the considered system over the Gamma-Gamma (GG) fading to study the efficacy of aperture selection to combat jammers when AT conditions vary. The rest of the paper is organized as follows. Section 2 introduces the system model and builds up the mathematical framework of the work. In Section 3, error analysis is carried for a generalized \(N\) user transmitters with a jammer, and asymptotic behavior of the same is studied. The numerical results and discussion are presented in Section 4. Section 5 concludes the work.