Resource Allocation for Energy-Efficient Cellular Communications via Aerial IRS

In this paper, we present a resource allocation framework for uplink communication in cellular networks aided with aerial intelligent reflecting surface (IRS). The main focus is on maximizing the energy efficiency by jointly optimizing the transmit powers of the users, the active beamforming at the base stations, and the passive beamforming at the IRS, while maintaining the users' minimum rates and adhering to the power constraints. The formulated problem is a highly intractable non-convex one, with the optimization variables coupled with each other in an intricate manner. To tackle this, an iterative solution based on alternating techniques is proposed. In particular, the transmit beamforming and the phase-shift matrix are obtained by minimum mean square error and semidefinite relaxation techniques, respectively. Numerical results are provided and show that using aerial IRS has remarkable advantages compared to the system operation with conventional aerial relaying. In particular, significant energy efficiency gains are achieved when optimal transmit power and a large number of reflecting elements are implemented.