Optimal Placement of Transmissive RIS in the Near Field for Capacity Maximization in THz Communications

TL;DR

This paper investigates the optimal placement of transmissive RIS in the near field for THz MIMO systems, revealing that placement depends on antenna spacing and can enhance spatial multiplexing by exploiting wavefront curvature.

Contribution

It introduces a novel analysis of near-field RIS placement in THz MIMO, showing that optimal positioning depends on inter-antenna spacing rather than just proximity.

Findings

RIS can induce wavefront curvature in the far field

Optimal RIS placement depends on Tx and Rx antenna spacing

Near-field RIS placement enhances spatial multiplexing

Abstract

This study centers on Line-of-Sight (LoS) MIMO communication enabled by a Transmissive Reconfigurable Intelligent Surface (RIS) operating in the Terahertz (THz) frequency bands. The study demonstrates that the introduction of RIS can render the curvature of the wavefront apparent over the transmit and receive arrays, even when they are positioned in the far field from each other. This phenomenon contributes to an enhancement in spatial multiplexing. Notably, simulation results underline that the optimal placement of the RIS in the near-field is not solely contingent on proximity to the transmitter (Tx) or receiver (Rx) but relies on the inter-antenna spacing of the Tx and Rx.