Employing antenna selection to improve energy efficiency in massive MIMO systems

Massive multi-input-multi-output systems promise high data rates by using a large number of antennas, which also increases the power usage of the system as a consequence. This creates an optimization problem that specifies how many antennas the system should use to operate with maximal energy efficiency (EE). Our main goal is to consider a base station with a fixed number of antennas, such that the system can operate with a smaller subset of antennas according to the number of active user terminals, which may vary over time. Thus, in this paper, we propose an antenna selection algorithm, which selects the best antennas according to the better channel conditions with respect to the users, aiming at improving the overall EE. Then, due to the complexity of the mathematical formulation, a tight approximation for the consumed power is presented, using the Wishart theorem, and it is used to find a deterministic formulation for the EE. Simulation results show that the approximation is quite tight and that there is significant improvement in terms of EE when antenna selection is used.