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A critical problem in wireless sensor networks research and application is the efficient handling of the nodes' energy under the point of interest (PoI) coverage constraint. Since the sensors are randomly deployed in the field some PoIs are covered only by a few sensors. Thus, the maximum achieved network lifetime is upper bounded by the energy of the sensors that cover the most poorly covered targets. In this talk, we tackle this problem by either dividing the nodes in sets so that only one set is active at any time or by moving some sensors to poorly covered areas from areas that are covered by many sensors. The first approach is mathematically proven to be an NP-complete problem so sub-optimal solutions, like centralised or localised heuristics are proposed. The second approach requires the use of mobile nodes to move from one PoI to another and may drain the nodes energy when the distance between the PoIs is high. Advantages and disadvantages of the two approaches will be discussed.
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