Proactive adaptations in sensor network query processing

Wireless sensor networks (WSN) are used by many applications for event and environmental monitoring. Due to the resource-limited nodes in WSNs, there has been much research into extending the functional lifetime of the network through energy-saving techniques. Sensor Network Query Processing (SNQP) is one such technique. SNQP uses information about a query and the WSN over which it is to be run, to generate an energy-efficient Query Execution Plan (QEP) that distributes processing in the form of QEP fragments to the nodes in the WSN. However, any QEP is likely to drain the batteries of the nodes unevenly, and, as a result, nodes used in a QEP may run out of energy when there are significant energy stocks still available in the WSN. An adaptive query processor could react to energy depletion, for example, by generating a revised plan that refrains from using the drained nodes. However, adapting only when a node has been depleted may provide few opportunities for the creation of effective new QEPs. In this paper, we introduce an approach that determines, at query compilation time, a sequence of QEPs with switch times for transitioning between successive plans with a view to extending the overall lifetime of the query. We describe how this approach has been implemented as an extension to an existing SNQP and present experimental results indicating that it can significantly increase QEP lifetimes.