Cognitive radio in 5G: a perspective on energy-spectral efficiency trade-off

A cognitive cellular network, which integrates conventional licensed cellular radio and cognitive radio into a holistic system, is a promising paradigm for the fifth generation mobile communication systems. Understanding the trade-off between energy efficiency, EE, and spectral efficiency, SE, in cognitive cellular networks is of fundamental importance for system design and optimization. This article presents recent research progress on the EE-SE trade-off of cognitive cellular networks. We show how EE-SE trade-off studies can be performed systematically with respect to different architectures, levels of analysis, and capacity metrics. Three representative examples are given to illustrate how EE-SE trade-off analysis can lead to important insights and useful design guidelines for future cognitive cellular networks.