Massive MIMO systems promise high data rates by employing large number ofantennas, which also increases the power usage of the system as a consequence.This creates an optimization problem which specifies how many antennas thesystem should employ in order to operate with maximal energy efficiency. Ourmain goal is to consider a base station with a fixed number of antennas, suchthat the system can operate with a smaller subset of antennas according to thenumber of active user terminals, which may vary over time. Thus, in this paperwe propose an antenna selection algorithm which selects the best antennasaccording to the better channel conditions with respect to the users, aiming atimproving the overall energy efficiency. Then, due to the complexity of themathematical formulation, a tight approximation for the consumed power ispresented, using the Wishart theorem, and it is used to find a deterministicformulation for the energy efficiency. Simulation results show that theapproximation is quite tight and that there is significant improvement in termsof energy efficiency when antenna selection is employed.
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