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CRNP: A cover-based relay node placement algorithm to delay-constrained wireless sensor networks

Wireless Sensor Networks (WSNs) are gradually employed in many applications requiring real-time data transmission. As hop count is an important factor affecting end-to-end delay, in this paper, we investigate the Hop Constrained Relay Node Placement (HCRNP) problem where at least one path fulfilling the hop constraint is built between each Sensor Node (SN) and the sink. To address this problem, we present a Cover-based Relay Node Placement (CRNP) algorithm which places Relay Nodes (RNs) from SNs to the sink. Through formulating the deployment of RNs in each iteration as a cover problem (the set cover problem for arbitrary settings or the discrete unit disk cover problem for special settings) with respect to hop constraint, the CRNP algorithm iteratively deploys RNs adjacent to the SNs or the previously placed RNs so as to gradually connect SNs to the sink. Through rigorous analysis, we show that the CRNP algorithm has an approximation ratio better than existing algorithms for the HCRNP problem (i.e., O(1) for special settings and O(ln n) for arbitrary settings, where n is the number of SNs). Finally, we conduct extensive simulations to verify the effectiveness of the proposed algorithm.