Owing to the promising ability of saving hardware cost and spectrum resources, integrated sensing and communication (ISAC) is regarded as a revolutionary technology for future sixth-generation (6G) networks. The mono-static ISAC systems considered in most of existing works can only achieve limited sensing performance due to the single observation angle and easily blocked transmission links, which motivates researchers to investigate cooperative ISAC networks. In order to further improve the degrees of freedom (DoFs) of cooperative ISAC networks, the transmitter-receiver selection, i.e., base station (BS) mode selection problem, is meaningful to be studied. However, to our best knowledge, this crucial problem has not been extensively studied in existing works. In this paper, we consider the joint BS mode selection, transmit beamforming, and receive filter design for cooperative cell-free ISAC networks, where multi-BSs cooperatively serve communication users and detect targets. We aim to maximize the sum of sensing signal-to-interference-plus-noise ratio (SINR) under the communication SINR requirements, total power budget, and constraints on the numbers of transmit/receive BSs. An efficient joint beamforming design algorithm and three different heuristic BS mode selection methods are proposed to solve this non-convex NP-hard problem. Simulation results demonstrates the advantages of cooperative ISAC networks, the importance of BS mode selection, and the effectiveness of our proposed algorithms.

翻译：凭借节省硬件成本和频谱资源的潜在能力，集成感知与通信（ISAC）被视为第六代（6G）未来网络的革命性技术。现有大多数工作考虑的单站ISAC系统由于观测角度单一且传输链路易受阻，仅能实现有限的感知性能，这促使研究人员探索合作式ISAC网络。为进一步提升合作式ISAC网络的自由度（DoFs），发射-接收选择（即基站模式选择问题）具有重要研究价值。然而，据我们所知，这一关键问题尚未在现有工作中得到广泛研究。本文针对合作式无蜂窝ISAC网络，研究了联合基站模式选择、发射波束赋形与接收滤波器设计问题——其中多基站协同服务通信用户并探测目标。我们旨在满足通信信干噪比（SINR）要求、总功率预算及发射/接收基站数量约束的条件下，最大化感知信干噪比之和。针对这一非凸NP难问题，提出了高效的联合波束赋形设计算法与三种启发式基站模式选择方法。仿真结果验证了合作式ISAC网络的优越性、基站模式选择的重要性以及所提算法的有效性。