Joint Beamforming and Phase Shifting Design Towards Energy-Efficient RIS-Aided Cell-Free Network

Abstract

In this paper, we investigate optimization methods for joint beamforming and phase shifting in downlink recon-figurable intelligent surface aided cell-free network. Towards green communication demand, maximizing energy efficiency performance is considered, which is a nonconvex objective. Firstly, we employ zero-forcing beamforming to simplify and decouple the optimization problem into phase shifting problem and power allocation problem. Then, the objective function of the phase shifting problem is approximately on cosine function of a marginal phase shift. Based on this, we use alternating optimization to solve the problem. Finally, the power allocation problem is globally optimized by the algorithm based on Benson's method. The computational complexity of the proposed algorithm depends linearly on the scale of RISs. The simulation results show that our proposed algorithm can effectively improve the energy efficiency performance and fast converge.