Beam Training and Alignment for RIS-Assisted Millimeter Wave Systems:State of the Art and Beyond

TL;DR

This paper reviews current beam training methods for RIS-assisted millimeter wave systems, introduces a new multi-directional approach with reduced overhead, and discusses open challenges in the field.

Contribution

It provides a comprehensive review of existing solutions and proposes a novel multi-directional beam training method for RIS-assisted mmWave systems.

Findings

The new method achieves good beam alignment with low training overhead.

Review highlights advantages and limitations of current beam training solutions.

Outlines open issues for future research in RIS-assisted mmWave beam training.

Abstract

Reconfigurable intelligent surface (RIS) has recently emerged as a promising paradigm for future cellular networks. Specifically, due to its capability in reshaping the propagation environment, RIS was introduced to address the blockage issue in millimeter Wave (mmWave) or even Terahertz (THz) communications. The deployment of RIS, however, complicates the system architecture and poses a significant challenge for beam training (BT)/ beam alignment (BA), a process that is required to establish a reliable link between the transmitter and the receiver. In this article, we first review several state-of-the-art beam training solutions for RIS-assisted mmWave systems and discuss their respective advantages and limitations. We also present a new multi-directional BT method, which can achieve a decent BA performance with only a small amount of training overhead. Finally, we outline several important open issues in BT for RIS-assisted mmWave systems.