This work initiates the study of a beyond-diagonal reconfigurable intelligent surface (BD-RIS)-aided transmitter architecture for integrated sensing and communication (ISAC) in the millimeter-wave (mmWave) frequency band. Deploying BD-RIS at the transmitter side not only alleviates the need for extensive fully digital radio frequency (RF) chains but also enhances both communication and sensing performance. These benefits are facilitated by the additional design flexibility introduced by the fully-connected scattering matrix of BD-RIS. To achieve the aforementioned benefits, in this work, we propose an efficient two-stage algorithm to design the digital beamforming of the transmitter and the scattering matrix of the BD-RIS with the aim of jointly maximizing the sum rate for multiple communication users and minimizing the largest eigenvalue of the Cramer-Rao bound (CRB) matrix for multiple sensing targets. Numerical results show that the transmitter-side BD-RIS-aided mmWave ISAC outperforms the conventional diagonal-RIS-aided ones in both communication and sensing performance.

翻译：本文首次研究了毫米波频段下，用于集成感知与通信的超对角可重构智能表面辅助发射架构。在发射端部署超对角可重构智能表面不仅缓解了对大量全数字射频链的需求，还同时提升了通信与感知性能。这些优势得益于超对角可重构智能表面全连接散射矩阵带来的额外设计灵活性。为实现上述优势，本文提出了一种高效的两阶段算法，用于设计发射端的数字波束赋形与超对角可重构智能表面的散射矩阵，其目标是联合最大化多个通信用户的总和速率，并最小化多个感知目标的克拉美-罗界矩阵的最大特征值。数值结果表明，相较于传统对角可重构智能表面辅助方案，发射端超对角可重构智能表面辅助的毫米波集成感知与通信在通信与感知性能上均表现更优。