Integrated Sensing and Relay Communication for Low-Altitude Networks With Wireless Energy Transfer: A Two-Stage Design

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While uncrewed aerial vehicles (UAVs) have been widely deployed in low-altitude economy networks, their limited onboard energy capacity severely hinders long-period operations. To address this energy constraint, simultaneous wireless information and power transfer (SWIPT) provides a promising solution to charge UAVs flexibly. However, the energy harvesting efficiency of SWIPT depends on accurate UAV location information, which is often unavailable in practice. To address this challenge, we propose an integrated sensing and communication (ISAC)-assisted SWIPT scheme for LAE networks. The scheme adopts a two-stage design, i.e., an ISAC stage and a SWIPT stage. In the ISAC stage, multistatic sensing is performed with the cooperation of a ground base station, a ground user, and an aerial base station (ABS) to estimate the target UAV’s location. In the SWIPT stage, based on the estimated location, the ABS performs robust wireless energy transfer to the target UAV while accounting for location uncertainty. In our design, the ABS also serves as an aerial relay node for two-way communication between the ground base station and ground user. Additionally, the ABS is equipped with fluid antennas (FAs) that introduce additional spatial degrees of freedom to enhance localization accuracy, wireless power transfer, and relay transmission. In the ISAC stage, a joint optimization of the receiver filter, transmit beamforming, and FA positions is formulated to minimize the sensing Cramér–Rao bound (CRB), and in the SWIPT stage, another optimization problem is formulated to maximize the harvested energy. Simulation results demonstrate the effectiveness of our proposed design. Specifically, the robust wireless energy transfer design under localization uncertainty improves the energy harvesting efficiency compared to the conventional scheme. Moreover, leveraging the FAs can further help reduce the CRB and enhance energy delivery.