A hierarchical discovery scheme for WSNs with Mobile Elements

In sparse wireless sensor networks the distance between neighboring nodes is larger than the transmission range of sensor nodes and data collection is typically accomplished through specialized mobile nodes. If visit times of mobile nodes are not known in advance a discovery protocol is required for energy-efficient and timely mobile node´s detection. In this work we propose a simple yet effective hierarchical discovery protocol based on two different Beacon messages emitted by the mobile node (i.e., Long-Range Beacons and Short-Range Beacons). Our preliminary results show that, although very simple, the proposed scheme can provide a significant energy reduction with respect to the commonly used scheme based on a single Beacon, especially if the discovery phase is long.