  The carbon footprint concern in the development and deployment of 5G new
radio systems has drawn the attention to several stakeholders. In this article,
we analyze the critical power consuming component of all candidate 5G system
architectures-the power amplifier (PA)-and propose PA-centric resource
management solutions for green 5G communications. We discuss the impact of
ongoing trends in cellular communications on sustainable green networking and
analyze two communications architectures that allow exploiting the extra
degrees-of-freedom (DoF) from multi-antenna and massive antenna deployments:
small cells/distributed antenna network and massive MIMO. For small cell
systems with a moderate number of antennas, we propose a peak to average power
ratio-aware resource allocation scheme for joint orthogonal frequency and space
division multiple access. For massive MIMO systems, we develop a highly
parallel recurrent neural network for energy-efficient precoding. Simulation
results for representative 5G deployment scenarios demonstrate an energy
efficiency improvement of one order of magnitude or higher with respect to
current state-of-the-art solutions.
