The optimum number of base station antennas in an energy efficient downlink massive MIMO system

In this paper, a solution to determine the optimum number of base station antennas in an energy efficient downlink massive multiple-input multiple-output (MIMO) system using the zero-forcing (ZF) precoding scheme with imperfect channel state information is provided. In the case where an arbitrary number of base station antennas are used, a recent study has shown that, as the reliability of the channel estimation increases from zero, the total downlink transmit power initially increases to a certain point before decreasing. By using the optimum number of antennas derived in this paper, the results show that, the initial rise in power with increasing reliability of the channel estimation is eliminated.