Wireless Sensor Networks (WSNs) can be viewed as energy constrained database systems, and join query processing is a very important topic in the field of sensor based systems. Join query for WSNs in a multi-dimensional and continuous way has not been widely explored, as well as is not energy efficient enough. In this paper, we proposed a continuous Multi-attribute Join Query Processing (MJQP) within latest sampling periods for WSNs based applications. We developed a filter-based scheme to discard non-joining tuples, which the center points of filters are identified and updated. Besides, we design an optimized solution to reduce the transmission of non-joining tuples, which is very benefit on energy efficiency. Experiments on real-world data set show that our methods outperform the centralized algorithm.
Early detecting the approaching events is the primary way of minimizing their damages in the sensor-based systems. The majority of existing approaches of event description and detection rely on using crisp raw sensory data, which requires large amount of data transmission as well as is memory-consuming, moreover, these approaches are only applicable to homogeneous sensor networks. This paper describes a novel efficient framework for event prewarning in sensor networks with multi microenvironments, which mainly includes a simple and practical data preprocessing method, Node-level Noteworthy Event (NNE) detection algorithm, event probability encodings of NNEs and two distributed Node-level Alert Event (NAE) detection algorithms. We demonstrate our algorithms by experimentally evaluating their performance in various scenarios using real and synthetic data. Our NAE detection algorithm by leveraging spatial correlation only requires a small amount of data transmission and can detect over 90% of NAEs with few false negatives.
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