Maximizing energy efficiency in off-peak hours: A novel sleep scheme for WLAN access points

The number of wireless access points (APs) have increased rapidly in recent years to support increasing demands of wireless local area network. However, some of the research findings show that many of these APs are actually idle mainly during off-peak hours, i.e., there is no active user to support within their coverage areas during that time. Nevertheless, to identify availability of users, all APs are remained powered-on always regardless the presence or absence of any active user inside their coverage areas. To save energy during off-peak hours in idle APs, sleep mechanism could be applied. In this paper, we propose a novel sleep mechanism for IEEE 802.11 wireless local area network APs. In our solution, an AP moves into sleep mode to maximize its energy efficiency (EE) while not harming traffic delay requirements. To decide length of sleep interval of an AP, we propose a dynamic sleep boundary decision algorithm which dynamically sets upper and lower bound of sleep duration considering traffic arrival rate and traffic delay requirements at a given time. Numerical results show the proposed scheme can improve EE of an AP significantly compared to the existing schemes without violating traffic delay requirements.