QoS Aware Query Processing Algorithm for Wireless Sensor Networks

Abstract—In sensor networks, continuous query is commonly used for collecting periodical data from the objects under monitoring. This sort of queries needs to be carefully designed, in order to minimize the power consumption and maximize the lifetime of the sensor nodes. Data reduction techniques can be employed to decrease the size and frequency of data to be transferred in the network, and therefore save energy. This paper presents a novel method for optimizing sliding window based continuous queries. In particular, we deal with two categories of aggregation operations: stepwise aggregation (e.g. MAX, MIN, SUM, COUNT, AVERAGE, etc.) and direct aggregation (e.g. MEDIAN). Our approach is, by using packet merging or compression techniques, to reduce the data size to the best extent, so that the total performance is optimal. A QoS weight item is specified together with a query, in which the importance of the four factors, power, delay, accuracy and error rate can be expressed. Then an optimal query plan can be obtained by studying all the factors simultaneously, leading to the minimum cost. System models for energy and time consumptions of communication are created. Problem is formalized and algorithm is described in detail. Finally, experiments are conducted to validate the effectiveness of the proposed method