This paper studies an integrated sensing and communication (ISAC) system for single-target detection in a cloud radio access network architecture. The system considers downlink communication and multi-static sensing approach, where ISAC transmit access points (APs) jointly serve the user equipments (UEs) and optionally steer a beam toward the target. A centralized operation of cell-free massive MIMO (multiple-input multiple-output) is considered for communication and sensing purposes. A maximum a posteriori ratio test detector is developed to detect the target in the presence of clutter, so-called target-free signals. Moreover, a power allocation algorithm is proposed to maximize the sensing signal-to-interference-plus-noise ratio (SINR) while ensuring a minimum communication SINR value for each UE and meeting per-AP power constraints. Two ISAC setups are studied: i) using only existing communication beams for sensing and ii) using additional sensing beams. The proposed algorithm's efficiency is investigated in both realistic and idealistic scenarios, corresponding to the presence and absence of the target-free channels, respectively. Although detection probability degrades in the presence of target-free channels that act as interference, the proposed algorithm significantly outperforms the interference-unaware benchmark by exploiting the statistics of the clutter. It has also been shown that the proposed algorithm outperforms the fully communication-centric algorithm, both in the presence and absence of clutter. Moreover, using an additional sensing beam improves the detection performance for a target with lower radar cross-section variances compared to the case without sensing beams.

翻译：本文针对云无线接入网络架构下的单目标检测问题，研究了一体化感知与通信系统。该系统采用下行链路通信与多站协同感知方法，其中一体化感知与通信接入点联合为用户设备提供服务，并可选择性地向目标方向引导波束。考虑采用无蜂窝大规模MIMO的集中式操作实现通信与感知功能。为在杂波（即目标不存在信号）存在情况下检测目标，本文提出了一种最大后验概率比检验检测器。此外，提出了一种功率分配算法，在确保每个用户设备最小通信信干噪比并满足每个接入点功率约束的条件下，最大化感知信干噪比。研究了两种一体化感知与通信架构：1）仅利用现有通信波束进行感知；2）采用额外感知波束。在理想场景（无目标信道不存在）和实际场景（存在无目标信道）下验证了所提算法的效率。尽管作为干扰的无目标信道会降低检测概率，但所提算法通过利用杂波统计特性，显著优于不考虑干扰的基准算法。研究表明，无论是否存在杂波，所提算法均优于完全以通信为中心的算法。此外，与无感知波束情况相比，采用额外感知波束可提升对低雷达散射截面积方差目标的检测性能。