In this research, we propose a relay node deployment method, named as Greedy-Search (GS) method, for placing additional relay nodes to improve the network connectivity of disconnected WSNs. By using a geometric search algorithm, every relay node is placed at a proper location, which results in significant reducing the number of required relay nodes. Besides, by considering radio propagation effect, a realistic model for estimating the connectivity of a radio link is proposed, which yields accurate network topology determination especially for applying the method in indoor environment. Simulation results prove that the proposed method has the best performance in average number of relay nodes comparing to related works. It is found that the proposed method provides significant improvements on ANRN comparing to related works, when the node density is in the region of 0.002~0.011 nodes/m2. The average improvement ratio of ANRN is 22.5%, 38.6%, and 40.9%, in LOS, NLOS with obstacles, NLOS with obstacles and small-scale fading, respectively, when the node density is equal to 1/250 nodes/m2. It indicates that there are about 20% of improvement contributed by the proposed two dimension geometric search algorithm, and about 30% of improvement due to the accurately determining of network topology by using the proposed link connectivity estimation model.
Due to the proposed method significantly reduces the number of relay nodes, it slightly decrease node degree comparing to the MST-based and VW methods.
However, by examining the obtained ANNCs, the proposed method always provides connected WSNs after deploying relay nodes, especially in NLOS environment with heavy obstacles. Above all, the proposed method is an effective and efficient method for relay node deployment.
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