Energy-efficient mobile targets detection in the presence of mobile sinks

Tracking moving targets has become an increasingly important application for sensor networks. Sensor nodes may sense moving targets far away from the Source, and hence a large amount of energy may be wasted by them to send sensory data to the Source. Designing efficient algorithms and protocols for data dissemination to mobile sinks is an interesting research and engineering issue, especially for large-scale wireless sensor networks (WSNs). Sink mobility brings new challenges to the design of data dissemination. The location updates for each mobile sink need to be continuously propagated through the field to all sensor nodes, so that future data reports can be correctly delivered to the sink. As energy and resources of a sensor node are limited, these algorithms and protocols should meet a high energy efficiency and a high delivery ratio. To deal with this issue, we propose a framework, called Tree Overlay Grid (TOG), for data collection and dissemination. To route queries and deliver data efficiently in our framework, a geometric routing GFB (Greedy Forwarding within Bound) is proposed to create a TTDD-like grid network, and a tree protocol is used to construct local trees around sinks. In addition, two mechanisms are introduced to prolong the network lifetime. The first mechanism tries to save energy by reducing the traffic load; the second one tries to slow down energy consumption by balancing the traffic load. The simulation results show that TOG outperforms the best known data collection solution and some current data collection solutions for WSNs with multiple mobile sinks.