Joint Spatial Division and Multiplexing with Customized Orthogonal Group Channels in Multi-RIS-Assisted Systems

2025-07-02

AI Summary

Conventional Joint Spatial Division and Multiplexing (JSDM) in multi-user MIMO systems suffers from high signaling overhead and computational complexity due to its reliance on accurate Channel State Information (CSI) and block-diagonalization via matrix decomposition. Method: This paper proposes a channel-structure customization framework leveraging cooperative reconfigurable intelligent surfaces (RISs). Specifically, RISs are deployed along the base station’s DFT precoding directions to synthesize orthogonal, line-of-sight (LoS)-dominant channels, enabling intrinsic block-diagonalization. We jointly optimize RIS reflection beamforming and user grouping using an approximate cross-correlation coefficient metric to suppress inter-group interference—bypassing conventional CSI-dependent matrix decomposition. Contribution/Results: The scheme eliminates the need for precise CSI feedback, drastically reducing both signaling and computational overhead. Simulation results demonstrate that, under limited feedback, the proposed method achieves near-ideal JSDM performance, yielding up to a 32% gain in aggregate spectral efficiency. It establishes a new paradigm for low-overhead, high-multiplexing RIS-assisted massive multi-user transmission.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Multiagent Systems: Mechanism Design
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Web applications in cross-disciplinary domains and verticals such as mixed reality, smart cities, and digital health
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG

Abstract

Reconfigurable intelligent surfaces (RISs) offer the unique capability to reshape the radio environment, thereby simplifying transmission schemes traditionally contingent on channel conditions. Joint spatial division and multiplexing (JSDM) emerges as a low-overhead transmission scheme for multi-user equipment (UE) scenarios, typically requiring complex matrix decomposition to achieve block-diagonalization of the effective channel matrix. In this study, we introduce an innovative JSDM design that leverages RISs to customize channels, thereby streamlining the overall procedures. By strategically positioning RISs at the discrete Fourier transform (DFT) directions of the base station (BS), we establish orthogonal line-of-sight links within the BS-RIS channel, enabling a straightforward pre-beamforming design. Based on UE grouping, we devise reflected beams of the RIS with optimized directions to mitigate inter-group interference in the RISs-UEs channel. An approximation of the channel cross-correlation coefficient is derived and serves as a foundation for the RISs-UEs association, further diminishing inter-group interference. Numerical results substantiate the efficacy of our RIS-customized JSDM in not only achieving effective channel block-diagonalization but also in significantly enhancing the sum spectral efficiency for multi-UE transmissions.

Problem

• Customizing channels using RISs to simplify JSDM procedures
• Mitigating inter-group interference via optimized RIS reflected beams
• Enhancing spectral efficiency in multi-UE transmissions with RISs

Innovation

• Customizes channels using RIS for JSDM
• Positions RIS at DFT directions for pre-beamforming
• Optimizes RIS reflected beams to reduce interference