Spatiotemporal delay control for low-duty-cycle sensor networks

Data delivery is a major function of sensor network applications. Many applications, such as military surveillance, require the detection of interested events to be reported to a command center within a specified time frame, and therefore impose a real-time bound on communication delay. On the other hand, to conserve energy, one of the most effective approaches is to keep sensor nodes in the dormant state as long as possible while satisfying application requirements. Obviously a node can not communicate if it is not active. Therefore, to deliver data in a timely manner for such extremely low duty-cycle sensor networks, communication needs to be carefully managed among sensor nodes. In this work, we introduce three different approaches to provide real-time guarantee of communication delay. First, we present a method for increasing duty-cycle at individual node. Then we describe a scheme on placement of sink nodes. Based on previous two methods, we discuss a hybrid approach that shows better balance between cost and efficiency on bounding communication delay. Our solution is global optimal in terms of minimizing the energy consumption for bounding pairwise end-to-end delay. For many-to-one and many-to-many cases, which are NP-hard, we propose corresponding heuristic algorithms for them. To our knowledge, these are the most generic and encouraging results to date in this new research direction. We evaluate our design with an extensive simulation of 5,000 nodes as well as with a small-scale running test-bed on TinyOS/Mote platform. Results show the effectiveness of our approach and significant improvements over an existing solution.