Sleep Scheduling in Critical Event Monitoring with Wireless Sensor Networks

In this paper, we focus on the applications of wireless sensor networks (WSNs) for critical event monitoring, where normally there are only small number of packets need to be transmitted, while when urgent event occurs, the alarm should be broadcast to the entire network as soon as possible. During the event monitoring, a sleep scheduling is taken to prolong the lifetime of WSN, which causes significant transmission delay. In this paper, we propose a sleep scheduling to greatly reduce the alarm broadcasting delay in WSNs. A nice feature of our proposed scheme is that the broadcasting delay is irrelative to the number of nodes in WSN, and the upper bound of it is just 3D/2+2L, where D is the maximal diameter hop of the network and L is the length of sleeping duty cycle, the unit is the length of time slot t set according to the quality of wireless links. As each node only needs to wake up for no more than t in each duty cycle, the proposed sleep scheduling has an ultra low energy consumption. Moreover, the proposed scheme can work well in unreliable wireless communication environment with enlarging the size of t to allow sensor nodes retransmit several times when there is failure. Extensive simulations are conducted to evaluate the performance of the proposed sleep scheduling, and experiments with 64 MicaZ sensor nodes are also made to validate the proposed scheme in real wireless communication environment.