## 1 Introduction  
The past few years have witnessed enormous attention from academia and industry to free-space optical (FSO) communication. This is primarily due to advantages, such as unlicensed spectrum, higher speed, low implementation cost, and many more [1]. These benefits have led to the extensive application of FSO technology, from terrestrial to satellite communication. However, there exist a few challenges in FSO communication such as atmospheric turbulence (AT) and pointing error (PE) [2]. AT occurs due to a random change in the refractive index of air with time, classified into weak, moderate, strong, and saturation. On the other hand, PE is an aftereffect of the misalignment of the transmitter and receiver, leading to the loss of line-of-sight between the two. It causes error enhancement or complete failure of an FSO link, depending upon its severity [3]. Many techniques have been devised to improve the FSO communication. Multiple-input multiple-output (MIMO) communication techniques are proposed to scale down the effect of channel fading due to AT and PE in the optical channel [4, 5, 6, 7]. It is a requisite to improve the diversity order (equitable to the number of signals at the receiver enduring deep fade independently) while also pruning the system complexity and power requirements. Transmit aperture (LEDs/LASERs) selection is an attractive low-cost and low-complexity spatial diversity technique that can significantly increase the quality of the received signal and enhance the immunity to turbulence-induced fading in FSO systems [8, 9]. In this technique, a single transmit aperture, which experiencesthe maximum channel gain, is selected for uncoded transmission during a transmission interval; all other apertures are kept inactive [10]. The antenna selection technique is also favored for FSO systems, as it outperforms the repetition coding (RC) scheme [11]. However, the inherent property of FSO communication being unregulated bears consequences in the form of it being vulnerable to any unsolicited network that may disrupt or attack the legitimate flow of information [12]. An FSO communication system's susceptibility to jammers mainly comes from two reasons: a confined range of operating wavelength and broad field-of-view (FoV). Typically, an FSO system is allowed to use limited wavelengths--usually, either 1300 nm or 1550 nm [13] to tackle attenuation and satisfy the eye-safety rules--making it not very laborious to access its operating wavelength. Moreover, FoV is the solid angle through which a detector is exposed to an incoming optical signal [1]. A receiving aperture's FoV is often kept broad as it tackles the fading in the channel due to AT and PE. Many terrestrial applications such as storage area networks, enterprise connectivity, etc., require aperture averaging and a wide FoV, despite the transceiver's fixed position to mitigate the effects of building sway, seismic activity, or physical obstruction [14]. In satellite communication, wider FoV is even more essential since the transceivers are mobile and very far from each other [15; 16; 17; 18]. Having said that, a wider FoV gives room to any jammer to compromise an FSO link's security or cause complete link failure. Furthermore, as FSO transceivers are placed many feet above the ground, even for terrestrial communication, it is easy to locate them and establish a jammer in their FoV. The jammer can be a malignant optical transmitter with very large power at its disposal to increase the bit error of the authentic communication of user information among FSO transceivers. It can transmit a pulse towards the receiver to disrupt the communication as it is a challenge to decipher the legitimate signal from the jammed received signal. Hence, it is imperative to study jamming in an FSO communication system and devise different techniques to combat it. In the literature, the general mechanism of FSO communication has been studied by [19]. In [20], a proficient discussion on FSO communication is presented. Ref.