Optimizing Rate-CRB Performance for Beyond Diagonal Reconfigurable Intelligent Surface Enabled ISAC

• Published in: IEEE communications letters p. 1
• Main Authors: Zhang, Xiaoqi, Liu, Liang, Zhang, Shuowen, Zhu, Weifeng, Zhang, Haijun
• Format: Journal Article
• Language: English
• Published: IEEE 2025
• Subjects: Array signal processing; Beyond diagonal reconfigurable intelligent surface (BD-RIS); Cramér-Rao bound (CRB); Downlink; Integrated sensing and communication; integrated sensing and communication (ISAC); Location awareness; Manifolds; Optimization; Receiving antennas; Reconfigurable intelligent surfaces; Riemannian steepest ascent method; Scattering; Signal to noise ratio
• ISSN: 1089-7798; 1558-2558
• DOI: 10.1109/LCOMM.2025.3599597

This letter considers a beyond diagonal reconfigurable intelligent surface (BD-RIS) aided integrated sensing and communication (ISAC) system, where the BD-RIS can help a multi-antenna base station (BS) serve multiple user equipments (UEs) and localize a target simultaneously. We formulate an optimization problem that designs the BS beamforming matrix and the BD-RIS scattering matrix to maximize UEs' sum rate subject to a localization Cramér-Rao bound (CRB) constraint and an additional unitary matrix constraint for the scattering matrix. Because unitary matrices form a manifold, our problem belongs to constrained manifold optimization. This letter proposes a log-barrier based Riemannian steepest ascent method to solve this problem effectively. Numerical results verify the effectiveness of our algorithm and the performance gain of the BD-RIS aided ISAC systems over the conventional RIS aided ISAC systems.