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.
@article{arxiv.2505.02254,
title = {Tri-Hybrid Multi-User Precoding Based on Electromagnetically Reconfigurable Antennas},
author = {Pinjun Zheng and Yuchen Zhang and Tareq Y. Al-Naffouri and Md. Jahangir Hossain and Anas Chaaban},
journal= {arXiv preprint arXiv:2505.02254},
year = {2025}
}