Power Scaling Law for Optical IRSs and Comparison with Optical Relays

TL;DR

This paper investigates the power scaling laws of optical IRSs in free-space optical systems, analyzing how various parameters influence their performance and comparing them with optical relays in different regimes.

Contribution

It provides a comprehensive analysis of the power scaling laws for optical IRSs and compares their performance with optical relays under various conditions.

Findings

Optical IRSs can exhibit linear, quadratic, or saturated power scaling depending on system parameters.

Relay-assisted FSO links outperform IRSs at high SNRs, but IRSs are better at low SNRs.

Optimal IRS placement depends on the power scaling regime, unlike relays which are best placed equidistant.

Abstract

The line-of-sight (LOS) requirement of free-space optical (FSO) systems can be relaxed by employing optical relays and optical intelligent reflecting surfaces (IRSs). Unlike radio frequency (RF) IRSs, which typically exhibit a quadratic power scaling law, the power reflected from FSO IRSs and collected at the receiver lens may scale quadratically or linearly with the IRS size or may even saturate at a constant value. We analyze the power scaling law for optical IRSs and unveil its dependence on the wavelength, transmitter (Tx)-to-IRS and IRS-to-receiver (Rx) distances, beam waist, and lens size. We compare optical IRSs in different power scaling regimes with optical relays in terms of the outage probability, diversity and coding gains, and optimal placement. Our results show that, at the expense of a higher hardware complexity, relay-assisted FSO links yield a better outage performance at high signal-to-noise-ratios (SNRs), but optical IRSs can achieve a higher performance at low SNRs. Moreover, while it is optimal to place relays equidistant from Tx and Rx, the optimal location of IRSs depends on the power scaling regime they operate in.