On maximizing the delivery ratio of ultra low duty-cycle WSNs under real-time constraints

Duty-cycle prolongs the lifetime of battery-powered wireless sensor networks (WSNs). However, it incurs additional delay because the nodes may be asleep. In addition to energy constraints, many applications have real-time constraints, which means the sink has to be informed before a deadline when an event occurs. Moreover, wireless links among low power radios are highly unreliable. These pose big challenges to design protocols for real-time applications. In this paper, a novel forwarding scheme based on distributed wakeup scheduling is proposed which can guarantee bounded delay and have higher delivery ratio for ultra low duty-cycle WSNs under unreliable links. The proposed wakeup scheduling algorithm schedules the wakeup time of each node according to the hop number and expected delivery ratio to the sink. We model the forwarding scheme and analyze its properties. Simulation results show that the proposed algorithm has better performances in terms of delivery ratio and end-to-end delay.