Intelligent metasurfaces are one of the favorite technologies for integrating sixth-generation (6G) networks, especially the reconfigurable intelligent surface (RIS) that has been extensively researched in various applications. In this context, a feature that deserves further exploration is the frequency scattering that occurs when the elements are periodically switched, referred to as Space-Time-Coding metasurface (STCM) topology. This type of topology causes impairments to the established communication methods by generating undesirable interference both in frequency and space, which is worsened when using wideband signals. Nevertheless, it has the potential to bring forward useful features for sensing and localization. This work exploits STCM sensing capabilities in target detection, localization, and classification using narrowband downlink pilot signals at the base station (BS). The results of this novel approach reveal the ability to retrieve a scattering point (SP) localization within the sub-centimeter and sub-decimeter accuracy depending on the SP position in space. We also analyze the associated detection and classification probabilities, which show reliable detection performance in the whole analyzed environment. In contrast, the classification is bounded by physical constraints, and we conclude that this method presents a promising approach for future integrated sensing and communications (ISAC) protocols by providing a tool to perform sensing and localization services using legacy communication signals.

翻译：智能超表面是集成第六代（6G）网络的关键技术之一，尤其是可重构智能表面（RIS）已在多种应用场景中得到广泛研究。在此背景下，当超表面单元周期切换时产生的频率散射特性（即时空编码超表面（STCM）拓扑结构）值得进一步探索。这类拓扑结构通过在频率域和空间域产生有害干扰，对现有通信方式造成损害，尤其在宽带信号应用时会进一步恶化。尽管如此，该技术仍具有推动感知与定位功能发展的潜力。本研究利用基站下行窄带导频信号，探索STCM在目标检测、定位与分类中的感知能力。这种新方法的研究结果表明，根据散射点（SP）的空间位置，可实现对散射点亚厘米级至亚分米级的定位精度。我们还分析了相关的检测与分类概率，在全部分析环境下均显示出可靠的检测性能。相比之下，分类性能受到物理条件限制。我们得出结论：该方法通过利用传统通信信号实现感知与定位服务，为未来集成感知与通信（ISAC）协议提供了一种具有前景的技术路径。