Secure energy efficiency maximization in cell-free networks with sub-connected active reconfigurable intelligent surface

Abstract

We consider a cell-free network security energy efficiency (SEE) scheme based on sub-connected active reconfigurable intelligent surface (RIS), where the multiple phase shifters share a power amplifier at RIS to achieve the purpose of reducing system energy consumption and saving costs. A joint base station (BS) and RIS beamforming optimizing problem of maximizing SEE is constructed, which includes the constraints of maximum transmission power, active RIS maximum power, phase shifter amplitude and amplification factor. Since the optimization problem is non-convex, the fractional programming method is used to decouple the objection function, and then the successive convex approximation, Alternating Direction Method of Multipliers, and Majorization-Minimization techniques are employed to alternately optimize to obtain the solutions of the original problem. Finally, simulation results demonstrate the effectiveness of the proposed scheme.