Performance Analysis and Optimization for Network-Assisted Full-Duplex Cell-Free Multi-Static ISAC Systems

The cooperative cell-free (CF) multi-static integrated sensing and communication (ISAC) network is a promising technology for sixth-generation (6G) communication, aiming to meet diverse scenarios and service demands. This paper puts forward a deployment framework of multi-static ISAC leveraging network-assisted full-duplex (NAFD) technology, which can perform target sensing and communicate with downlink (DL) and uplink (UL) users simultaneously. Initially, we analyze the communication and sensing performance of the NAFD CF multi-static ISAC system and substantiate the benefits of this system architecture. Then, to handle the challenge posed by the highly coupled DL and UL transmissions and enhance system performance, we delve into the joint optimization of access point (AP) mode selection and joint sensing and communication (JSC) beamforming design (AMJBD) within NAFD CF multi-static ISAC systems. We innovatively design a tailored multi-agent hierarchical reinforcement learning (MAHRL) method to solve this problem, considering the inherent relationship between optimization variables and the collaborative benefits of CF architecture. Simulation experiments confirm the superior performance of the NAFD CF multi-static ISAC system architecture and validate that the proposed MAHRL-based AMJBD method can strike an optimal balance between communication and sensing performance, enhancing system efficiency.