Delivery ratio-maximized wakeup scheduling for ultra-low duty-cycled WSNs under real-time constraints

Duty-cycling prolongs the lifetime of battery-powered wireless sensor networks (WSNs). However, it incurs an additional delay because the nodes may be asleep. Energy constraint is not the only constraint in WSNs. 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. This poses major challenges for researchers who want 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 on the messages that are delivered, and can have higher delivery ratios 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 are in line with the mathematical model and show that the proposed algorithm has good performances in terms of delivery ratio, end-to-end delay and energy efficiency.