Interference Minimization in Beyond-Diagonal RIS-assisted MIMO Interference Channels

2025-03-25

AI Summary

In BD-RIS-aided MIMO interference channels, residual interference becomes severe under high transmit power. Method: We propose a two-stage beamforming framework: (i) modeling and designing a passive RIS reflection matrix beyond diagonal structure to minimize interference leakage (IL) at receivers, solved via unitary manifold optimization under unit-modulus constraints; (ii) jointly designing a robust multi-objective active precoder balancing SINR and sum rate. Contribution/Results: This work establishes the first systematic modeling and optimization paradigm for BD-RIS. The proposed max-sum-rate (max-SR) precoder achieves over 20% higher sum rate than min-IL and max-SINR baselines under moderate-scale RIS (M < 20) and high transmit power, demonstrating superior interference suppression and spectral efficiency.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Intelligent Robots: Learning & Optimization for ROB
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments

Abstract

This paper proposes a two-stage approach for passive and active beamforming in multiple-input multiple-output (MIMO) interference channels (ICs) assisted by a beyond-diagonal reconfigurable intelligent surface (BD-RIS). In the first stage, the passive BD-RIS is designed to minimize the aggregate interference power at all receivers, a cost function called interference leakage (IL). To this end, we propose an optimization algorithm in the manifold of unitary matrices and a suboptimal but computationally efficient solution. In the second stage, users' active precoders are designed under different criteria such as minimizing the IL (min-IL), maximizing the signal-to-interference-plus-noise ratio (max-SINR), or maximizing the sum rate (max-SR). The residual interference not cancelled by the BD-RIS is treated as noise by the precoders. Our simulation results show that the max-SR precoders provide more than 20% sum rate improvement compared to other designs, especially when the BD-RIS has a moderate number of elements ($M<20$) and users transmit with high power, in which case the residual interference is still significant.

Problem

• Minimize interference in BD-RIS-assisted MIMO channels
• Optimize passive and active beamforming in two stages
• Improve sum rate with max-SR precoders design

Innovation

• Two-stage passive and active BD-RIS beamforming
• Unitary matrix optimization for interference minimization
• Max-SR precoders enhance sum rate significantly