Tri-hybrid beamforming architectures have been proposed to enable energy-efficient communications systems in extra-largescale antenna arrays using low-cost programmable metasurface antennas. We study the tri-hybrid beamforming design for integrated sensing and communications (ISAC) to improve both communications and sensing performances. Specifically, we formulate a multi-objective optimization problem that balances communications signal-to-noise ratio (SNR) and the sensing power at a target direction, subject to constraints on the total power consumption and physical limitations inherent to the trihybrid beamforming architecture. We develop an efficient iterative algorithm in which the variables are updated in a closed form at each iteration, leading to a low-complexity and fast-execution design. Numerical results show that the tri-hybrid architecture improves spatial gain and energy efficiency, though with reduced beam alignment capability compared to conventional hybrid beamforming architectures.

翻译：三混合波束成形架构已被提出，旨在利用低成本可编程超表面天线，在超大规模天线阵列中实现高能效通信系统。本文研究用于集成感知与通信的三混合波束成形设计，以同时提升通信与感知性能。具体而言，我们构建了一个多目标优化问题，在总功耗约束及三混合波束成形架构固有物理限制下，权衡通信信噪比与目标方向上的感知功率。我们提出了一种高效的迭代算法，其中各变量在每次迭代中以闭合形式更新，从而实现低复杂度、快速执行的设计。数值结果表明，三混合架构提高了空间增益与能量效率，但与传统混合波束成形架构相比，其波束对准能力有所降低。