Toward reliable and efficient reporting in wireless sensor networks

Energy efficiency is one of the major concerns in wireless sensor networks, since it impacts the network lifetime. In this paper, we investigate the relationship between sensor network performance, particularly its lifetime, and the number of active reporting nodes N by using both analytical and simulation approaches. We first demonstrate that decreasing the number of reporting nodes increases the number of reports that need to be sent to the sink in order to achieve the desired information reliability regarding a detected event. On one side, we show that reducing the number of reporting nodes reduces the probability of collision occurrence. Based on these results and as the first main contribution, we derive the optimal number of reporting nodes N-opt_energy that minimizes the energy consumed to report reliably the occurrence of an event. In other words, we prove that limiting the reporting tasks of a detected event to a small subset of sensor nodes (i.e., N-opt_energy), instead of using all the sensor nodes in the event area, enables significant energy conservation. Furthermore, with regard to the latency properties, we show that the average time required to reliably report an event is a convex function of the number of reporting nodes, where the minimum is obtained for a given N-opt_latency not equal N-opt_energy. Consequently and as the second main contribution, we demonstrate that the fastest way to reliably report an event does not correspond to the optimal way of consuming the scarce network energy. The trade-off between these two requirements is sensor application specific, depending on this one particular need in terms of quality of service. To the best of our knowledge, we are the first to tackle the energy efficiency problem from this perspective while considering the energy-reliability-latency trade-offs.