Reduced-Complexity Intelligent Reflecting Surface Optimization for Single-Carrier Transmission in Frequency-Selective Fading Channel

In this paper, we propose a novel reduced-complexity intelligent reflecting surface (IRS) optimization for cyclic-prefixed single-carrier transmission, which optimizes IRS reflection coefficients by increasing the achievable information rate. More specifically, our algorithm is designed based on coherently combining a single dominant channel tap for IRS beamforming. We demonstrate that significant improvement of the achievable information rate of the system is accomplished by employing the IRS with appropriate optimization schemes. Furthermore, our proposed algorithm achieves nearly identical performance to solving the full optimization problem in line-of-sight (LoS) and non-LoS scenarios while maintaining a practical RIS optimization and detection complexity.