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.
Highlights
1.1 MotivationIn the present-days, many researchers try to give answer the question of how to guarantee the security of confidential messages in advanced wireless communication systems and communication services for the emerging implementation of 5G and beyond wireless networks [2]
We provide some numerical results and discussions on how the average secrecy capacity (ASC) of terrestrial free-space optical (FSO) links is enhanced by deploying multiple lasers at the legitimate transmitter
We evaluate the asymptotic ASC of MISO FSO systems for different turbulent conditions and taking into consideration different severity of pointing errors when the number of lasers sources is equal to M = {1, 2, 4, 6}
Summary
In the present-days, many researchers try to give answer the question of how to guarantee the security of confidential messages in advanced wireless communication systems and communication services for the emerging implementation of 5G and beyond wireless networks [2]. Physical layer security (PLS) has been considered as an attractive research field to complement traditional encryption methods [3], [4]. Over the last few decades, many interesting articles have been reported from the informationtheoretic security point of view, especially in radio-frequency (RF) systems [5]–[8] (and references therein), which provide comprehensive analysis to notably improve the PLS through fading channels in terms of the secrecy outage probability (SOP) and the average secrecy capacity (ASC) via multiple-input/multiple-output (MIMO) systems, cooperative communication and cognitive networks, among others. According to the great improvement achieved in PLS aspects of RF systems by MIMO techniques, it is expected that this kind of transmission presents a remarkably impact on PLS aspects related to optical wireless communication systems
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