Offline-Online Design for Energy-Efficient IRS-Aided UAV Communications

In this correspondence, we consider the intelligent reflecting surface (IRS) assisted unmanned aerial vehicle (UAV) uplink transmission, where a UAV collects data from ground users via an IRS. The objective is to maximize the energy efficiency (EE) by jointly optimizing the UAV trajectory, user scheduling and IRS phase shifts. Unlike existing offline designs, we propose a hybrid offline-online scheme to further improve the performance with both the statistical and instantaneous channel state information (CSI). Specifically, the UAV trajectory and user scheduling are optimized based on the statistical CSI in the offline phase, followed by the online phase in which the phase shifts are readjusted based on the instantaneous CSI. Simulation results show the EE gain of the offline-online design over benchmarks.