Energy Efficiency Beamforming Design for UAV Communications With Broadband Hybrid Polarization Antenna Arrays

Stringent physical resource constraints in unmanned aerial vehicle (UAV) communications bring new challenges to energy efficient transmission. In this paper, we study energy efficient beamforming for UAV communications, where a wideband hybrid polarized antenna array with tapped-delay-lines (TDLs) structure is deployed on the UAV. By exploiting hybrid structured, TDLs, and polarized antenna arrays, the strict requirements of hardware size and cost on UAV can be satisfied. It is shown that the energy efficient beamforming with the adopted array can be formulated as a WMMSE-based parameter optimization problem, which however is still a challenging nonconvex problem due to unit modulus constraints in analog beamformer. To overcome the nonconvex nature, an iterative algorithm is proposed, in which the optimization problem is iteratively solved through three convex quadratic programming problems with convex equality or inequality constraints. Finally, the numerical results demonstrate that the proposed wideband beamforming algorithm can significantly improve the energy efficiency, compared with the gradient projection algorithm.