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 obtain 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., 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-base stations (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 transmitters and receivers. 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 joint design algorithms.

翻译：由于在节省硬件成本和频谱资源方面极具潜力，一体化感知与通信（ISAC）被视为未来第六代（6G）网络的革命性技术。现有大部分工作考虑的单一静态ISAC系统，因单一观测角度和易阻塞的传输链路，仅能获得有限的感知性能，这促使研究者探索协作ISAC网络。为进一步提升协作ISAC网络的自由度（DoFs），发射-接收选择问题（即基站模式选择问题）具有重要的研究意义。然而，据我们所知，这一关键问题在现有工作中尚未得到广泛研究。本文针对协作无小区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（BSs）协同服务通信用户并探测目标。在满足通信信干噪比（SINR）要求、总功率预算以及发射机与接收机数量约束下，我们旨在最大化总感知信干噪比。针对这一非凸NP-hard问题，本文提出了一种高效的联合波束赋形设计算法及三种不同的启发式基站模式选择方法。仿真结果验证了协作ISAC网络的优越性、基站模式选择的重要性以及所提联合设计算法的有效性。