The latest assessments of the emerging technologies for reconfigurable intelligent surfaces (RISs) have indicated the concept's significant potential for localization and sensing, either as individual or simultaneously realized tasks. However, in the vast majority of those studies, the RIS state (i.e., its position and rotation angles) is required to be known a priori. In this paper, we address the problem of the joint three-dimensional (3D) localization of a hybrid RIS (HRIS) and a user. The most cost- and power-efficient hybrid version of an RIS is equipped with a single reception radio-frequency chain and meta-atoms capable of simultaneous reconfigurable reflection and sensing. This dual functionality is controlled by adjustable power splitters embedded at each hybrid meta-atom. Focusing on a downlink scenario where a multi-antenna base station transmits multicarrier signals to a user via an HRIS, we propose a multistage approach to jointly estimate the metasurface's 3D position and 3D rotation matrix (i.e., 6D parameter estimation) as well as the user's 3D position. Our simulation results verify the validity of the proposed estimator via extensive comparisons of the root-mean-square error of the state estimations with the Cram\'{e}r-Rao lower bound (CRB), which is analytically derived. Furthermore, it is showcased that there exists an optimal hybrid reconfigurable intelligent surface (HRIS) power splitting ratio for the desired multi-parameter estimation problem. We also study the robustness of the proposed method in the presence of scattering points in the wireless propagation environment.

翻译：对可重构智能表面（RIS）新兴技术的最新评估表明，该概念在定位与感知方面具有显著潜力，既可单独实现也可同步完成上述任务。然而，在绝大多数研究中，RIS的状态（即其位置与旋转角度）需预先已知。本文解决了混合RIS（HRIS）与用户的联合三维（3D）定位问题。最具成本效益和能效的混合型RIS仅配备单接收射频链和能够同时实现可重构反射与感知的超原子，该双重功能通过嵌入每个混合超原子中的可调功率分配器控制。针对多天线基站经HRIS向用户发送多载波信号的下行链路场景，我们提出一种多阶段方法，用于联合估计超表面的3D位置与3D旋转矩阵（即6D参数估计）以及用户的3D位置。仿真结果通过将状态估计的均方根误差与分析推导的克拉美-罗下界（CRB）进行广泛对比，验证了所提估计器的有效性。此外，研究表明所需的多数值估计问题存在最优的混合可重构智能表面（HRIS）功率分配比。我们还研究了无线传播环境中存在散射点时该方法的鲁棒性。