Placement of relay nodes is a critical issue in provisioning large-scale wireless sensor networks. Lifetime and connectivity are the two most important factors that need to be considered. However, some relay nodes can consume much more energy due to heavier traffic, affecting the balanced lifetime of the whole network. In this paper, we propose a novel two-tiered distributed relay node placement strategy to achieve connectivity under the constraint of the expected network lifetime, while the number of relay nodes is effectively decreased. In the proposed node placement strategy, by dynamically adapting the location and data amount of relay nodes, we guarantee that sensor nodes and relay nodes consume the same amount of energy in each round of data transmission, thus ensuring a more balanced network lifetime. We first calculate the maximized network lifetime, and then achieve the network connectivity by effectively placing relay nodes under this constraint using the proposed strategy. Furthermore, we also propose two algorithms to effectively decrease the number of relay nodes, i.e. data distribution and data aggregation. Extensive experiments provide an in-depth analysis on the different factors affecting the number of relay nodes and the verification of the effectiveness of the proposed node placement strategy under different network lifetimes.
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