Energy Efficient Base Station Transmit Power Adaptation for Green 5G Massive MIMO Systems

Characterising the fundamental energy efficiency (EE) limits of massive Multiple-Input-Multiple-Output (MIMO) systems is significant for the development of green wireless communications. This paper analyses the adaptation of optimal BS transmitted power according to channel conditions and users' Quality of Service (QoS) requirements. The optimal BS transmitted power has the potential to be utilised as an effective strategy to reduce BSs power consumption and consequently enhance the EE of the system. Thus, this paper conducts an analytical closed-form expression of optimal downlink BS transmitted power for massive MIMO systems with Zero Forcing (ZF) beamforming processing and perfect Channel State Information (CSI). User required data rate and maximum allowable outage probability are considered as users' QoS constraints. Both of theoretical and the simulation results, for several transmission modes, indicate that the average EE per BS is a unimodal function of the user required data rate that jointly increased up to the maximum point of EE, but further increases in the data rate can only come at a loss in average EE per BS. As the higher the data rate, the higher the circuit and transmit power consumption, due to the need for a larger number of BS antennas. The results indicate that system EE can be enhanced by reducing energy consumption through optimal BS transmitted power. This is achieved by adaptation to channel conditions and users' QoS requirements.