A Cascaded Multi-IRSs Beamforming Method in mmWave Communication Systems

TL;DR

This paper proposes a novel cascaded multi-IRS beamforming method for mmWave systems that enhances coverage in dense urban environments by decomposing a complex optimization problem into manageable sub-problems and deriving a closed-form solution.

Contribution

It introduces a new joint design approach for multi-IRS phase shifts and BS precoding in mmWave systems, addressing a challenging non-convex optimization problem.

Findings

Improved coverage in dense urban areas verified by simulations.

Effective decomposition of the optimization problem into sub-problems.

Closed-form sub-optimal solution achieved for joint beamforming.

Abstract

In this paper, we study how to jointly design the phase shift of cascaded multi-IRSs and the precoding vector of the BS to improve the coverage in dense urban areas. We aim to maximize the signal-to-noise ratio (SNR) of the user equipment (UE) received signal by employing this method. However, it is a constrained non-convex optimization problem and is NP-hard. In order to solve this problem, we simplify it by utilizing the characteristic of the mmWave wireless system to decompose the optimization problem into multiple sub-optimization problems. By employing the asymptotic orthogonality of wireless channel in mmWave system to solve the sub-optimization problems, we finally yield a closed-form sub-optimal solution. The simulation results verify that our solution can effectively improve the coverage of deep dense urban areas.