Energy efficient resource optimization and transmission strategies for hyper-cellular mobile communication systems

Abstract

This paper provides an overview on our research on energy-efficient resource optimization and transmission strategies for hyper-cellular systems over the past five years. It summarizes the fundamental relationship between energy efficiency (EE) and spectral efficiency (SE), as well as the impact of physical resources on the relationship, such as time, frequency, antenna, and cache, and reviews the energy-efficient transmission strategies adapted to dynamic channels and traffic. It is in the context of key technologies in fifth-generation (5G) mobile communication systems, including massive centralized/distributed antenna systems, ultra-dense networks (UDNs), device-to-device (D2D) communications, and coordinated multi-point transmission (CoMP). It is shown that the EE-SE relationship in all representative systems exhibits a “bell-shaped curve”, meaning SE and EE increase simultaneously when SE is low while there is a tradeoff between SE and EE otherwise. Furthermore, the SE loss in EE-optimal policies is low, but the EE loss in SE-optimal policies is high. EE approaches zero with an increase in the number of antennas. Universal frequency reuse can maximize EE when the base station (BS)-to-user density ratio is large while partial frequency reuse is better for EE otherwise. Caching at BSs can improve EE and EE gain is high in scenarios with weak interference, low-capacity backhaul, and large content popularity skewness.