JOURNAL OF COMPUTERS (JCP)
ISSN : 1796-203X
Volume : 3    Issue : 11    Date : November 2008

QoS Aware Query Processing Algorithm for Wireless Sensor Networks
Jun-Zhao Sun
Page(s): 32-41
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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.

Index Terms
Sensor networks, Query processing, Data gathering, QoS, aggregation