Hotspot-Oriented Green Frameworks for Ultrasmall Cell Cloud Radio Access Networks

Sleep-mode operation of base stations aims to switch OFF some hardware modules to reduce power consumption while not degrading the quality of service. In this paper, novel hotspot-oriented green frameworks based on sleep-mode operation of remote radio heads (RRHs) are proposed for cloud radio access networks (C-RANs). The tradeoff between the reduction in power consumption of RRHs and the increase in transmission power at user equipment (UE) is first analyzed based on realistic models for ultrasmall cell C-RANs. In the proposed energy-efficient frameworks, corresponding clustering strategies are adopted to ensure that active RRHs are located as near as possible to hotspot areas for different infrastructure conditions and information availabilities. This reduces the increase in the uplink transmission power while maximizing the overall RRH power reduction. The green frameworks are modeled using C-RANs based on random topologies. It is shown that area power consumption can be reduced by more than 79% at a low traffic level compared with no sleep-mode operation. One of the frameworks is also compared with a baseline strategy that deals with hotspot areas and shows a 70% reduction in UE transmission power. The pros and cons of applying different frameworks are also investigated and analyzed.