Coupling-Aware RHS Beamforming for Wideband Multi-User Sum Rate Maximization

TL;DR

This paper introduces a coupling-aware wideband RHS model and a joint beamforming framework that significantly improves multi-user sum rate by accounting for mutual coupling effects in densely packed reconfigurable holographic surfaces.

Contribution

It develops a physically interpretable electromagnetic model and an efficient optimization algorithm for wideband RHS beamforming considering mutual coupling effects.

Findings

Experimental verification of the coupling model.

Simulation results show improved sum rate performance.

The proposed method effectively manages mutual coupling in wideband RHS systems.

Abstract

Wideband multi-user transmission assisted by reconfigurable holographic surfaces (RHSs) is fundamentally limited by mutual coupling effect among densely packed sub-wavelength radiation elements. This paper develops a coupling-aware wideband RHS model and an efficient joint beamforming framework to maximize the multi-user sum rate under practical feeder power and RHS excitation power constraints. We establish an electromagnetic equivalent model based on magnetic-dipole elements and a physically interpretable coupling decomposition into free space near field coupling and guided surface wave coupling. For optimization, we employ a weighted minimum mean square error (WMMSE)-based block coordinate method with a closed-form digital precoder update and introduce a Jacobian-aided coupling consistent hologram update that preserves coupling sensitivity via a first-order surrogate while keeping the hologram subproblem convex and efficiently solvable by projected first-order methods. Meep experiments verify the correctness of the proposed coupling model, and the simulations for a 28~GHz, 1~GHz-bandwidth RHS downlink prove the effectiveness of Jacobian-aided WMMSE-based method.