IRS-Assisted FSO System for LEO Satellites Constellations

In this work, we explore the use of intelligent reflecting surfaces (IRSs) as transparent relays in free-space optical (FSO) links for low earth orbit (LEO) satellites constellations. We introduce a novel IRS design featuring a slightly convex surface geometry to broaden the reflected beam, thereby mitigating the beam alignment challenges typically encountered in satellite-based FSO systems. We investigate the impact of IRS size, curvature, and transmitter beam width on end-to-end system performance, taking into account attenuation, atmospheric turbulence, and pointing errors. To accommodate the effects of surface curvature, we enhance and refine the channel pointing model and derive novel closed-form expressions for key performance metrics, including bit error rate, outage probability, and ergodic capacity. Numerical results based on realistic system parameters confirm the effectiveness of the proposed approach, albeit at the cost of increased geometric channel losses. Finally, we carry out numerical simulations to validate the new channel model and derived closed-form expressions, providing valuable insights for the design of future non-terrestrial networks architectures based on FSO systems.