Recently, Wireless Sensor Networks (WSN) have been used in many monitoring applications, e.g., environment monitoring. A WSN consists of a set of nodes, each having one or more sensors to measure a phenomena. Nodes are connected to each other using wireless radio communications. Typically, there is at least one base station that functions as an interface between the monitored area and the end-user.

In many applications, users are interested in statistical summaries of the observed data, e.g., histograms reflecting the distribution of the collected values. In this project we had two main contributions:

1. An efficient algorithm for answering Histogram queries in a WSN.
2. Efficient algorithms for answering snapshot and continuous Median queries in a WSN.

While designing applications for the WSN, the main challenge is the battery life time. For WSN nodes, sending a message consumes a significantly higher amount of energy than processing information inside the node. Therefore, we design our proposed algorithms in order to minimize the energy consumption and/or transmission cost, i.e. number of sent bytes, and consequently extend its lifespan. Our experimental results, using synthetic and real datasets, show that our proposed solutions are indeed able to substantially extend the lifespan of the WSN when compared to previously proposed solutions.

Publications:

• Khaled Ammar, Mario A. Nascimento. “Continuous Median Queries in Wireless Sensor Networks“,  In Mobile Data Management (MDM), 16th International Conference, to-appear. IEEE, 2015.
• Niedermayer, Johannes, Mario A. Nascimento, Matthias Renz, Peer Kroger, Khaled Ammar, and Hans-Peter Kriegel. “Cost-Based Quantile Query Processing in Wireless Sensor Networks” In Mobile Data Management (MDM), 2013 IEEE 14th International Conference on, vol. 1, pp. 237-246. IEEE, 2013.
• Khaled Ammar, and Mario A. Nascimento. “Histogram and other aggregate queries in wireless sensor networks.” In Scientific and Statistical Database Management, pp. 527-536. Springer Berlin Heidelberg, 2011.
• Khaled Ammar, Mario A. Nascimento, and Johannes Niedermayer. “An adaptive refinement-based algorithm for median queries in wireless sensor networks.” In Proceedings of the 10th ACM International Workshop on Data Engineering for Wireless and Mobile Access, pp. 9-16. ACM, 2011.
• Khaled Ammar, and Mario A. Nascimento. “On the use of histograms for processing exact aggregate queries in wireless sensor networks.” In International Workshop on Data Management for Sensor Networks, vol. 8. 2011.
• Khaled Ammar, and Mario A. Nascimento. “Histogram and other aggregate queries in wireless sensor networks” Technical Report TR 11-03, Department of Computing Science, University of Alberta, 2011.