RIS-Aided Dual-Polarized MIMO: How Large a Surface is Needed to Beat Single Polarization?

TL;DR

This paper investigates how reconfigurable intelligent surfaces (RISs) can enhance dual-polarized MIMO systems, determining the necessary surface size to outperform single-polarized MIMO by analyzing capacity improvements.

Contribution

It derives capacity formulas for RIS-assisted DP and SP MIMO systems and studies the impact of RIS size on system performance, providing deployment guidelines.

Findings

RIS size significantly affects DP MIMO capacity

Proper RIS deployment can surpass SP MIMO performance

Analytical expressions guide RIS surface design

Abstract

Dual-polarized (DP) multiple-input-multiple-output (MIMO) systems have been widely adopted in commercial mobile wireless communications. Such systems achieve multiplexing and diversity gain by exploiting the polarization dimension. However, existing studies have shown that the capacity of DP MIMO may not surpass that of single-polarized (SP) MIMO systems due to the cross-polarization coupling induced by the propagation environment. In this letter, we employ reconfigurable intelligent surfaces (RISs) to address this issue and investigate how large the surface should be to ensure a better performance for DP MIMO. Specifically, we first derive the capacities of DP and SP MIMO systems with an RIS, and then study the influence of the RIS size on the system capacity. Our analyses reveal how to deploy the RIS in a DP MIMO scenario.