Tri-Hybrid Multi-User Precoding Based on Electromagnetically Reconfigurable Antennas

TL;DR

This paper explores tri-hybrid multi-user precoding using electromagnetically reconfigurable antennas, highlighting the benefits and limitations of pattern optimization and the importance of hardware realizability for practical performance gains.

Contribution

It introduces a spherical harmonics-based pattern optimization and a projection method to ensure physical realizability, analyzing their impact on system performance.

Findings

Pattern optimization improves sum rate performance.

Projection onto realizable sets reduces or negates performance gains.

Hardware limitations affect practical implementation.

Abstract

The tri-hybrid precoding architecture based on electromagnetically reconfigurable antennas (ERAs) is a promising solution for overcoming key limitations in multiple-input multiple-output communication systems. Aiming to further understand its potential, this paper investigates the tri-hybrid multi-user precoding problem using pattern reconfigurable ERAs. To reduce model complexity and improve practicality, we characterize each antenna's radiation pattern using a spherical harmonics decomposition. While mathematically tractable, this approach may lead to over-optimized patterns that are physically unrealizable. To address this, we introduce a projection step that maps the optimized patterns onto a realizable set. Simulation results demonstrate that spherical harmonics-based radiation pattern optimization significantly enhances sum rate performance. However, after projection onto a realizable set obtained from real ERA hardware, the performance gain is notably reduced or even negligible, underscoring the need for more effective projection techniques and improved reconfigurable antenna hardware.