Modeling and Design of IRS-Assisted FSO System Under Random Misalignment

The strong dependency of the free-space optical (FSO) communication systems on the line-of-sight link put forward an inevitable challenge. Motivated by this fact, in this work, we aim to present and analyze a practical approach to model and design the intelligent reflecting surface (IRS)-assisted FSO communication system incorporating the impact of random misalignment. Contrary to the existing literature, an insightful IRS-assisted FSO model is proposed to envision the impact of the crucial system parameters. To this end, we propose a geometric and misalignment loss (GML) model that incorporates the random statistical modeling of the angle of incidence and the angle of reflection corresponding to the transmitted laser beam. Therefore, the proposed GML model allows us to inspect a realistic transmission and reception scenario of an IRS-assisted FSO system. Moreover, unlike the existing works, we consider independent fading statistics between the laser source (transmitter)-IRS link and IRS-photodetector (receiver) link. All these considerations allow us to envision the performance of a practical IRS-assisted FSO system. Several analytical closed-form expressions corresponding to the statistical distribution functions concerning the proposed GML model are also derived. Our derived closed-form expressions can be used as mathematical tools to examine the performance of an IRS-assisted FSO system under random misalignment. Further, our key findings indicate that under the impact of the random misalignment, the non-orthogonality of the lens with respect to the beam-line significantly impacts the system performance. Furthermore, simulation results validate the presented analysis and reveal unprecedented insights for the proposed IRS-assisted FSO system design.