On the effect of antenna correlation and coupling on energy-efficiency of massive MIMO systems

Massive Multiple-Input-Multiple-Output (MIMO) systems deploying a large number of antennas at the base station (BS) have been shown to produce high spectral and energy efficiencies (EE) under the assumptions of increasing BS physical space and critical antenna spacing. We propose a more realistic system model considering a fixed physical space: incorporating coupling and correlation among the BS antennas while providing a realistic analysis of the power consumption using a new power consumption model, taking into account the circuit power consumptions as a function of the number of BS antennas. We also touch on the performance analysis of two practical low complexity detectors keeping EE into consideration. The simulation results obtained show that EE does not monotonically increase with the number of BS antennas. On the contrary, it is a decreasing concave or quasi concave function of the number of BS antennas depending on the detection technique used at the receiver. Also shown is that with decreasing spacing between the antennas, mutual coupling increases contributing towards reduction in EE. Our analysis thus shows that EE does not increase in a massive MIMO system when a large number of antennas are to be accommodated within a fixed physical space and the total power consumed is considered to be a function of the antennas.