Transmit-Receive Beamforming for ISAC-Enabled Multi-UAVs System

Integrated Sensing and Communication (ISAC) is a pivotal technology enabling next-generation 6G networks by seamlessly combining communication and sensing functionalities for emerging applications. However, practical ISAC deployments are often hindered by performance degradation in complex environments. Ground-based ISAC systems are susceptible to line-of-sight (LoS) blockages stemming from urban infrastructure and irregular terrain. While unmanned aerial vehicle (UAV)-based ISAC has gained prominence, current research predominantly focuses on single-UAV architectures, which exhibit limitations in sensing coverage, accuracy, and vulnerability to ground clutter interference. This paper presents a collaborative multi-UAV ISAC framework designed to address these shortcomings through coordinated transmit-receive beamforming and trajectory optimization. A system-level model characterizing cooperative sensing performance of multiple UAVs in clutter-rich environments is developed. An optimization problem is formulated to maximize the signal-to-clutter-plus-noise ratio (SCNR) subject to communication quality-of-service (QoS) constraints. The resulting non-convex problem is effectively solved utilizing an alternating optimization algorithm, decomposing it into tractable beamforming design and trajectory optimization sub-problems, both of which are converted into convex forms. Numerical simulations conducted under clutter scenarios demonstrate significant improvements in sensing robustness and communication reliability achieved by the proposed framework compared to single-UAV and clutter-agnostic approaches.