Phase-Shift Design and Channel Modeling for Focused Beams in IRS-Assisted FSO Systems

As a potential solution for the backhaul of next-generation mobile or low Earth orbit (LEO) satellites, free-space optical (FSO), has received much attention recently. Various techniques have been suggested for employing an intelligent reflecting surface (IRS) in FSO systems, such as anomalous reflection, power amplification, and beam splitting. It is also possible to deliver more power to the receiver (Rx) by collimating or focusing the reflected beam at the Rx lens. In this paper, we propose a phase-shift design of an IRS for beam focusing. In addition, we propose a new pointing error model and an outage performance analysis for the case when the beam width is comparable to or less than the aperture size of the Rx. The analytical results are validated by Monte Carlo simulations. This paper provides essential preliminary results for future research that assumes a focused beam in FSO systems.