Energy-efficient configuration of antennas and users in the downlink MIMO system

In this paper, we investigate the relationship of base station (BS) antennas and supportable users in the downlink multi-cell multi-user MIMO system to maximize system energy efficiency (EE). In order to study their relationship, we first analyze the channel capacity and derive the EE formula by considering a realistic power consumption model (PCM). Then we build an energy-efficient optimization model with respect to the number N_t of BS antennas and the number K of users. Due to the high optimization complexity, we derive an approximation of channel capacity to simplify the EE optimization. Based on the simplified optimization model, we propose a low-complexity optimization algorithm to obtain the optimum Nt and K. The simulation results suggest that the proposed algorithm can obtain the optimal configuration of BS antennas and supportable users and each user needs only about 2 BS antennas to maximize the EE with zero-forcing (ZF) precoding.