Recent advances in energy-efficient networks and their application in 5G systems

This article provides an overview on research in energy-efficient wireless networks during the past decade and discusses its potential applications toward the fifth generation cellular systems. After analyzing the trade-off between spectrum efficiency and energy efficiency, various research results are summarized within a framework of energy-efficient resource allocation with optimization as a common tool. Then potential energy efficiency improving approaches in both physical layer and deployment aspects are provided. Finally, energy efficiency related open problems in massive multiple-input multiple- output, device-to-device communications, ultra dense networks, and other emerging technologies are identified.