Multi-Resolution Codebook Design and Multiuser Interference Management for Discrete XL-RIS-Aided Near-Field MIMO Systems

TL;DR

This paper introduces a novel multi-resolution codebook design and interference management approach for XL-RIS-assisted near-field MIMO systems, addressing practical discrete phase-shift constraints and enhancing multiuser performance.

Contribution

It proposes a hierarchical beam training, joint and separate codebook construction methods, and a flexible interference management technique tailored for XL-RIS near-field MIMO systems with discrete phase shifts.

Findings

Enhanced beam pattern accuracy and user CSI estimation.

Superior interference management performance compared to benchmarks.

Effective hybrid precoding extension demonstrated through simulations.

Abstract

Extremely large-scale reconfigurable intelligent surface (XL-RIS) can effectively overcome severe fading and provide higher communication performance. However, current research on XL-RIS overlooks the discrete phase-shift characteristics of RIS in practical systems, which will result in significant performance degradation.In this paper, we investigate near-field communication schemes assisted by XL-RIS with discrete phase shifts.Specifically, we propose a hierarchical beam training method to obtain the user channel state information (CSI), and develop the jointly optimized codebook construction (JOCC) method and separately optimized codebook construction (SOCC) method for base station (BS) precoding and XL-RIS phase shifts, respectively. With JOCC, the most superior beam training performance can be obtained.With SOCC, higher performance than the single-antenna BS codebook can be obtained at a similar complexity.Further, we propose a flexible multiuser interference management (IM) method that is simple to solve. The IM method uses adaptive gain matrix approximation to take into account user fairness and can be solved in closed-form iterations. In addition, we extend the proposed method to a hybrid precoding design. Simulation results demonstrate that the proposed multi-resolution codebook construction method can obtain more accurate beam patterns and user CSI, and the proposed IM method obtains superior performance over the benchmark methods.