Integrated sensing and communication (ISAC) system stands out as a pivotal usage scenario of 6G. To explore the coordination gains offered by the ISAC technique, this paper introduces a novel communication-assisted sensing (CAS) system. The CAS system can endow users with beyond-line-of-sight sensing capability, wherein the base station with favorable visibility senses device-free targets, simultaneously transmitting the acquired sensory information to users. Within the CAS framework, we characterize the fundamental limits to reveal the achievable distortion between the state of the targets of interest and their reconstruction at the users' end. Finally, within the confines of this theoretical framework, we employ a typical application as an illustrative example to demonstrate the minimization of distortion through dual-functional waveform design, showcasing the potential of CAS in enhancing sensing capabilities.

翻译：集成感知与通信（ISAC）系统作为6G的关键应用场景脱颖而出。为探索ISAC技术带来的协调增益，本文提出了一种新型通信辅助感知（CAS）系统。该CAS系统能够赋予用户超视距感知能力，其中具有良好视距条件的基站探测无源目标，同时将获取的感知信息传输给用户。在CAS框架内，我们刻画了基本极限，以揭示感兴趣目标状态与用户端重构结果之间的可达失真。最后，在该理论框架的约束下，我们以典型应用为例，展示了通过双功能波形设计实现失真最小化的方法，彰显了CAS在增强感知能力方面的潜力。