RESCUE-ISAC: Energy-Efficient Active–Passive Beamforming for Emergency UAV-ISAC in 6G Networks
Emergency sixth-generation (6G) networks require rapid, reliable, and energy-efficient connectivity when terrestrial infrastructure is damaged or unavailable. Unmanned aerial vehicles (UAVs) with integrated sensing and communication (ISAC) capabilities can provide flexible aerial coverage while enabling situational awareness in disaster-affected areas. However, their performance is constrained by limited onboard energy, obstructed air-to-ground links, and the competing requirements of communication reliability and sensing accuracy. To address these challenges, this paper proposes RESCUE-ISAC, an energy-efficient reconfigurable intelligent surface (RIS)-assisted UAV-ISAC framework for emergency 6G networks. In the proposed system, a multi-antenna UAV serves ground emergency users and senses a target area, while an RIS improves the wireless propagation environment through passive beamforming. The energy-efficiency maximization problem is formulated as a joint optimization of UAV active beamforming and RIS phase shifts subject to communication signal-to-interference-plus-noise ratio (SINR), sensing signal-to-noise ratio (SNR), transmit power, and unit-modulus constraints. An alternating block-wise optimization approach is developed to solve the resulting non-convex problem. Simulation results demonstrate that RESCUE-ISAC improves energy efficiency, link reliability, sensing performance, mobility robustness, and runtime–performance trade-off compared with heuristic, lightweight, and optimization-based benchmark schemes.