Joint Beamforming and Trajectory Optimization for UAV-Enabled ISAC Under a Finite Energy Budget

This paper studies joint beamforming and trajectory optimization for integrated sensing and communication (ISAC) enabled by an energy-constrained unmanned aerial vehicle (DAV). The DAV transmits information-bearing signals using an onboard uniform linear array (ULA), for simultaneously serving downlink communication users and sensing multiple targets during its flight. To explore the synergy between UAV and ISAC, we jointly optimize the DAV's flight trajectory, ISAC beamforming, and mission completion time for maximizing the accumulated sensing energy for ground targets under a finite energy budget for the UAV, while guaranteeing quality-of-service for communication users. The formulated problem is highly non-convex, which is generally intractable. Motivated by the success of approximate dynamic programming (DP) methods, we propose a novel low-complexity high-quality solution by combining the one-step lookahead rollout algorithm in approximate DP and the semidefinite programming technique in convex optimization. Our simulation results show that, compared to two baseline schemes, the proposed scheme can significantly enlarge the achievable sensing and communication performance region for ISAC.