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

2025-08-25

AI Summary

Existing near-field MIMO systems assisted by XL-RIS often neglect the discrete phase-shift characteristics of RIS, leading to performance degradation in channel estimation and beamforming. Method: This paper proposes a hierarchical beam training and multi-user interference (MUI) co-management framework. It innovatively designs joint/separate-optimization multi-resolution codebooks to enable precise discrete-phase modeling, and introduces a closed-form adaptive gain-based interference management mechanism. The framework is further extended to a hybrid precoding architecture. Contribution/Results: The proposed method achieves low computational complexity while significantly improving near-field channel estimation accuracy and beam pattern directivity. Simulation results demonstrate superior beamforming gain and MUI suppression performance compared to state-of-the-art baseline schemes.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Machine Learning: Multi-instance/Multi-view Learning
• Multiagent Systems: Multiagent Learning

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Search and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for ranking

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.

Problem

• Designing discrete phase-shift codebooks for XL-RIS aided near-field MIMO systems
• Managing multiuser interference while ensuring user fairness in communication
• Overcoming performance degradation from practical discrete RIS phase-shift limitations

Innovation

• Hierarchical beam training for near-field CSI acquisition
• Jointly optimized discrete codebook for BS precoding
• Adaptive gain matrix for multiuser interference management