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，集成感知与通信(ISAC)为实现同步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基于视距假设，即感知目标需同时被感知发射端与接收端直接观测。这限制了ISAC系统在复杂环境（如城市低空空域）中的应用，此类环境通常存在信号阻塞与非视距多径传播问题。为应对这一挑战，本文提出一种创新方法，通过利用最初为环境感知无线通信而提出的信道知识地图新技术，实现环境感知的非视距ISAC。所提方法的主要创新在于：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"的优势。为此，感知目标被视为虚拟用户设备，将无线通信信道先验转化为感知信道先验，使得单一CKM可服务于双重目的。我们通过一种名为信道角度-时延图的特定CKM来阐释所提框架。具体而言，该框架利用CADM通过挖掘通信与感知角度-时延分布间的关联性，推导感知信道的角度-时延先验，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，相较于经典基于几何的感知方法，本方案性能显著提升，该结论进一步通过克拉美-罗下界分析得到验证。