Enhancing Secrecy Capacity in FSO Links via MISO Systems Through Turbulence-Induced Fading Channels With Misalignment Errors

Abstract

It has recently been proved that the free-space optical (FSO) communication links are susceptible to interceptions. Due to this reason, the optics community shows a special interest in studying these high-speed links in greater detail from a physical layer security (PLS) point of view. Therefore, in this paper, we propose, for the first time, enhancing the average secrecy capacity (ASC) in FSO links via multiple-input/single-output (MISO) systems. It is well-known that the fading effects in FSO channels can be significantly mitigated by exploiting spatial diversity techniques at the transmitter end. Thus, we develop a new asymptotic closed-form solution at high signal-to-noise-ratio (SNR) to accurately compute the ASC for MISO based FSO communication systems with equal gain combining (EGC) reception through generalized misalignment and atmospheric turbulence-induced fading channels. As a key feature, we investigate the impact of the eavesdropper's orientation along with its location in the pointing error model. We can conclude that the influence of the eavesdropper on recollecting radiated power is diminished considerably by increasing not only the normalized beam width at the receiver end, but also by increasing the number of laser sources. Numerical results are tested by exact Monte Carlo simulations.

A contemporary survey on free space optical communication: Potentials, technical challenges, recent advances and research direction

“…Saidi and Hamdi [408] presented BER performance for multihop hybrid RF/FSO systems using M-ary pulse positon modulation (MPPM) and MIMO technique under gamma-gamma turbulence channels. The enhancement of average secrecy capacity and improvement of secrecy outage probability for MIMO-FSO link with equal gain combing reception technique over gamma-gamma atmospheric turbulence channels is demonstrated first time in literature [409]. Ref [410] investigated satisfactory BER, power penalty reduction, and outage probability performance for 10 Gb/s QPSK FSO links using aperture averaging receive diversity and MIMO spatial technique.…”

Opportunistic Schedule Selection for Multiuser MIMO FSO Communications: A Security- Reliability Trade-Off Perspective

“…where, 𝑓 I (𝐼, 𝑘, 𝜃) = 9 >(R)S 3 𝐼 R+9 𝑒 +Q S ⁄ stands for the gamma PDF with shape parameter 𝑘 and scale parameter 𝜃. In (10) and (11),…”

“…For example, in a typical wiretap model, PLS theory states that secure communication is possible if the capacity of the legitimate channel is higher than that of the eavesdropping channel. Motivated by the PLS schemes of RF systems, various PLS techniques have been proposed to secure FSO communications, such as diversity approaches [10], [11], transmit aperture selection (TAS) [12], artificial noise injection [13], and generalized chaotic modulation [14]. However, many characteristics of FSO systems differ from RF systems (e.g., the channel, and the physical characteristics of the transmitting and receiving devices).…”

A Survey on Physical Layer Security for FSO Communication Systems

“…From a security standpoint, the IM/DD FSO system with CV-QKD technique was investigated [31]. In various recent works of literature [33]- [36], the inherent benefits of employing FSO based on transmitter spatial diversity [32] have been extended to improve PLS in FSO. In addition, [37]- [39] explored the security implications of hybridization between FSO and RF link.…”