Joint Precoding and Phase-Shift Optimization for Beyond-Diagonal RIS-Aided ISAC System

2026-03-10

AI Summary

This study addresses the flexible trade-off between communication and sensing performance in integrated sensing and communication (ISAC) systems assisted by bi-diagonal reconfigurable intelligent surfaces (BD-RIS). The work proposes a joint optimization framework for transmit precoding vectors and BD-RIS phase-shift matrices, enhancing sum-rate through multi-user interference management while improving sensing performance via an approximation of sensing beamforming gain. Notably, this is the first work to incorporate BD-RIS into ISAC systems, leveraging its inter-element connectivity to introduce additional degrees of freedom and enable synergistic co-optimization of communication and sensing. An alternating optimization algorithm is developed to efficiently solve the resulting non-convex weighted problem, yielding closed-form updates for both precoding and phase shifts. Simulation results demonstrate that the proposed scheme significantly outperforms conventional diagonal RIS in achieving a superior communication-sensing performance trade-off.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Security and Privacy: Large-scale security measurements

Abstract

Beyond diagonal reconfigurable intelligent surfaces (BD-RIS) can realize the interconnection between reflecting elements through the impedance network, thereby providing a new approach for the performance improvement of integrated sensing and communication (ISAC) systems. This paper investigates the optimization problem of BD-RIS-aided multiuser ISAC system, aiming to achieve the flexible design of trade-offs between communication and sensing performance. Specifically, we propose an optimization framework jointly combining the multiuser interference management and sensing beam gain approximation method. By jointly optimizing the precoding vector and RIS phase-shift matrix, improving the multiuser communication sum rate through the proposed interference management method, and enhancing the system sensing performance through the beam gain approximation method. For the resulting non-convex weighted optimization problem, we employ the alternating optimization (AO) algorithm to decouple it into two subproblems of precoding vector and phase-shift matrix optimization, with each step admitting closed-form solutions.Simulation results demonstrate that the proposed BD-RIS-aided ISAC system can achieve significant improvement in the trade-offs between communication and sensing performance than the traditional diagonal RIS, verifying the effectiveness of the proposed optimization framework.

Problem

• BD-RIS
• ISAC
• multiuser
• communication-sensing trade-off
• precoding

Innovation

• Beyond-Diagonal RIS
• Integrated Sensing and Communication
• Joint Precoding and Phase-Shift Optimization
• Alternating Optimization
• Beam Gain Approximation