Coupling-Aware RHS Beamforming for Wideband Multi-User Sum Rate Maximization
This work is significant for researchers and engineers working on reconfigurable intelligent surfaces and 6G wireless communication, as it tackles the practical problem of mutual coupling in wideband multi-user RHS systems.
This paper addresses the limitation of mutual coupling in wideband multi-user transmission using reconfigurable holographic surfaces (RHSs) by developing a coupling-aware wideband RHS model and a joint beamforming framework. The proposed Jacobian-aided WMMSE-based method for a 28 GHz, 1 GHz-bandwidth RHS downlink proves effective in maximizing the multi-user sum rate.
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.