Issue No. 07 - July (2007 vol. 19)
Minji Wu , Department of Computer Science, Hong Kong Baptist University, Kowloon Tong, KLN, Hong Kong
Jianliang Xu , Department of Computer Science, Hong Kong Baptist University, Kowloon Tong, KLN, Hong Kong
Xueyan Tang , School of Computer Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798
Wang-Chien Lee , Department of Computer Science and Engineering, The Penn State University, University Park, PA 16802
Top-k monitoring is important to many wireless sensor applications. This paper exploits the semantics of top-k query and proposes an energy-efficient monitoring approach called FILA. The basic idea is to install a filter at each sensor node to suppress unnecessary sensor updates. Filter setting and query reevaluation upon updates are two fundamental issues to the correctness and efficiency of the FILA approach. We develop a query reevaluation algorithm that is capable of handling concurrent sensor updates. In particular, we present optimization techniques to reduce the probing cost. We design a skewed filter setting scheme, which aims to balance energy consumption and prolong network lifetime. Moreover, two filter update strategies, namely, eager and lazy, are proposed to favor different application scenarios. We also extend the algorithms to several variants of top-k query, that is, order-insensitive, approximate, and value monitoring. The performance of the proposed FILA approach is extensively evaluated using real data traces. The results show that FILA substantially outperforms the existing TAG-based approach and range caching approach in terms of both network lifetime and energy consumption under various network configurations.
optimisation, wireless sensor networks
M. Wu, J. Xu, X. Tang and W. Lee, "Top-k Monitoring in Wireless Sensor Networks," in IEEE Transactions on Knowledge & Data Engineering, vol. 19, no. 7, pp. 962-976, 2008.