Energy Efficient Beamforming for User-Centric Virtual Cell Networks

Abstract

This paper aims to design beamforming vectors and cluster formation scheme by formulating an energy efficiency (EE) maximization problem in the user-centric networks, where several multi-antenna access points (APs) form a virtual cell to serve each single-antenna user equipment (UE). Considering both rate requirements and power budgets, we study the feasibility of the original EE maximization problem. To verify the feasibility, we design a max-min rate problem. Then, instead of solving the original problem directly, we deal with two subproblems: 1) relaxed EE maximization subproblem and 2) total power minimization subproblem. Through applying the weighted minimum mean square error (WMMSE) approach, we first transform the nonlinear data rate expression into a quadratic form and then solve each subproblem via using the Lagrangian dual method, which fortunately has closed-form solutions. Moreover, a novel threshold forming scheme is proposed for AP cluster formation and a simple but effective method called K-dimension grid search is devised to obtain the near-optimal threshold. The extensive simulation results indicate that our proposed algorithm converges fast and is robust to the simulation environment. In addition, the proposed algorithm outperforms the benchmark algorithms greatly in terms of EE and data rate.