Joint Beamforming for Continuous Transmissive RIS-Enabled Multiuser Communications

2026-10-05

AI Summary

This study addresses the challenging mixed finite- and infinite-dimensional non-convex optimization problem in continuously transmitting reconfigurable intelligent surface (RIS)-aided multi-user downlink systems. Based on a spherical wave channel model and finite-path field response vectors, this work jointly optimizes base station precoding and the continuous aperture phase profile to maximize the weighted sum rate. An alternating optimization framework, integrating the calculus of variations with the minorization-maximization technique, is developed to derive an exact closed-form solution for the infinite-dimensional phase function. Simulation results demonstrate that the proposed scheme significantly outperforms benchmark methods, fully validating the system gains achieved through spatially continuous phase control and a large effective receiving area.

Abstract

This paper studies continuous transmissive reconfigurable intelligent surface (CT-RIS)-enabled multiuser downlink communications, where passive beamforming is characterized by a phase function defined over the continuous aperture. We employ a distance-dependent spherical-wave model for the base station (BS)-to-CT-RIS link and introduce a finite-path model based on field-response vectors for the CT-RIS-to-user links. The resulting weighted sum rate maximization problem jointly optimizes the finite-dimensional BS precoders and the infinite-dimensional CT-RIS phase function, giving rise to a mixed finite- and infinite-dimensional non-convex optimization problem. To address this problem, we develop an alternating optimization algorithm that combines a closed-form BS precoder update with a functional phase update derived using the calculus of variations and minorization-maximization. Numerical results demonstrate that the proposed CT-RIS consistently outperforms the considered benchmarks, with the performance gains attributed to spatially continuous phase control and a larger effective receiving area.

Problem

• Continuous Transmissive RIS
• Joint Beamforming
• Multiuser Communications
• Weighted Sum Rate Maximization
• Non-convex Optimization

Innovation

• Continuous Transmissive RIS
• Joint Beamforming
• Calculus of Variations
• Alternating Optimization
• Spherical-wave Model