Latency of event reporting in duty-cycled wireless sensor networks

We consider duty cycling in sensor networks for time-critical monitoring, where sensors monitor events and send the information to a data collection node (called sink). Latency is considered as the delay elapsed between the time when an event occurs and the time when the sink gets the report. Such networks are different from general purpose ad hoc networks, where latency is defined as the delay elapsed between the time when a source node initiates a packet and the time when the destination node receives the packet. We aim to prolong network lifetime by scheduling periodic sensors' duty cycles while preserving small latency from events to the sink. In our duty cycle schemes, sensors are grouped into sets; the collaboration between different sets is designed to enable the availability of event reports at active sensors before they reach the sink. Our ideas are simple and achieve desirable properties: the network lifetime is proportional to the number of sets and the performance is comparable to that of non-duty-cycled networks with the same number of active sensors, as shown in our analyses and simulations.