As one of the key usage scenarios for the sixth generation (6G) wireless networks, integrated sensing and communication (ISAC) provides an efficient framework to achieve simultaneous wireless sensing and communication. However, traditional wireless sensing techniques mainly rely on the line-of-sight (LoS) assumptions, i.e., the sensing targets are directly visible to both the sensing transmitter and receiver. This hinders ISAC systems to be applied in complex environments such as the urban low-altitude airspace, which usually suffers from signal blockage and non-line-of-sight (NLoS) multi-path propagation. To address this challenge, in this paper, we propose a novel approach to enable environment-aware NLoS ISAC by leveraging the new technique called channel knowledge map (CKM), which was originally proposed for environment-aware wireless communications. One major novelty of our proposed method is that the same CKM built for wireless communication can be directly used to enable NLoS wireless sensing, thus enjoying the benefits of ``killing two birds with one stone''. To this end, the sensing targets are treated as virtual user equipment (UE), and the wireless communication channel priors are transformed into the sensing channel priors, allowing one single CKM to serve dual purposes. We illustrate our proposed framework by a specific CKM called \emph{channel angle-delay map} (CADM). Specifically, the proposed framework utilizes CADM to derive angle-delay priors of the sensing channel by exploiting the relationship between communication and sensing angle-delay distributions, enabling sensing target localization in the challenging NLoS environment. Extensive simulation results demonstrate significant performance improvements over classic geometry-based sensing methods, which is further validated by Cramér-Rao Lower Bound (CRLB) analysis.

翻译：作为第六代（6G）无线网络的关键应用场景之一，通感一体化（ISAC）为实现同时无线感知与通信提供了高效框架。然而，传统无线感知技术主要依赖视距（LoS）假设，即感知发射机与接收机均能直接观测到感知目标。这阻碍了ISAC系统应用于城市低空空域等复杂环境——此类环境常受信号遮挡与非视距（NLoS）多径传播影响。为应对这一挑战，本文提出一种基于信道知识地图（CKM）新技术的环境感知非视距通感一体化方法，该技术最初用于环境感知无线通信。本方法的主要创新点在于：为无线通信构建的同一CKM可直接用于实现非视距无线感知，从而获得“一石二鸟”之效。为此，我们将感知目标视为虚拟用户设备（UE），并将无线通信信道先验信息转换为感知信道先验信息，使单个CKM能够服务于双重目的。我们通过一种名为“信道角度时延地图（CADM）”的特定CKM来阐明所提框架：具体而言，该框架利用CADM通过挖掘通信与感知角度时延分布之间的关系，推导感知信道的角度时延先验信息，从而在具有挑战性的非视距环境中实现感知目标定位。大量仿真结果表明，相较于经典几何感知方法，本方法性能显著提升，且克拉美-罗下界（CRLB）分析进一步验证了该结论。