REQUEST: Region-Based Query Processing in Sensor Networks

In wireless sensor networks, node failures occur frequently. The effects of these failures can be reduced by using aggregated values of small groups of sensors instead of the values of individual sensors. However, most existing works have focused on computing the aggregation of all the nodes without grouping. Only a few approaches proposed the processing of grouped aggregate queries. However, since groups in their approaches are disjoint, some relevant regions to the query can be missing. In this paper, we propose REQUEST , region-based query processing in sensor networks. A region in our approach is defined as a maximal set of nodes located within a circle having a diameter specified in the query. To efficiently construct a large number of regions covering the entire monitoring field, we build the SEC (Smallest Enclosing Circle) index. Moreover, in order to process a region-based query, we adapt a hierarchical aggregation method, in which there is a leader for each region. To reduce the communication cost, we formulate an optimal leader selection problem and transform the problem into the set-cover problem. Finally, we devise a query-initiated routing tree for the communication between the leader and non-leader nodes in a region. In the experimental results, we show that the result of our region-based query is more reliable than that of the query which is based on individual nodes, and our processing method is more energy-efficient than existing methods for processing grouped aggregate queries.