Review and classification of the use of SMs for energy saving in next-generation radio access networks

Energy consumption in 5G/6G wireless networks presents a fundamental challenge, encompassing various aspects related to energy, availability, cost, and environmental concerns. According to the literature, the use of sleep modes (SMs) has emerged as an effective strategy to improve the energy efficiency of base stations (BS) within recently proposed 5G frameworks, while also considering future 6G developments. A comprehensive review is conducted to elucidate what SMs are, the decision process to switch to and from SM BSs, and the main challenges associated with them. Additionally, power consumption models are analyzed to understand how to evaluate the performance of SMs. Following an overview of the primary SM strategies developed in recent years, we introduce a matrix model classification of these strategies. This classification is based on the policies and tools implemented for SMs in wireless networks. Finally, based on this analysis, we highlight the most promising strategies and present ideas for future research aimed at achieving an energy-efficient and sustainable use of SMs in 5G/6G wireless networks.