Clustering achieves energy efficiency and scalable performance in wireless sensor networks (WSNs). A cluster is formed of several sensor nodes, one of them selected as the cluster head (CH). A CH collects information from the cluster members and sends aggregated data to the base station or another CH. In such a hierarchical WSN, some nodes are possibly moveable or nomadic (relocated periodically), while others are static. The mobility of sensor nodes can improve network performance and prolong network lifetime. This paper presents the idea of mobile, solar-powered CHs that relocate themselves inside clusters in such a way that the total energy consumption in the network is reduced and the network lifetime is extended. The positioning of CHs is made in each round based on a selfish herd hypothesis, where the leader retreats to the center of gravity. Based on this idea, the CH-active algorithm is proposed in this study. Simulation results show that this algorithm has benefits in terms of network lifetime and in the prolongation of the duration of network stability period.
A Wireless Sensor Network (WSN) assisted with Unmanned Aerial Vehicles (UAVs) is flexible and its lifetime becomes longer due to reduced energy consumption in the static sensor nodes. This paper analyses the capabilities of using UAVs in WSNs for enhancing various military and surveillance capabilities. It presents three architectures of UAV-aided WSNs and it uses a realistic simulation environment to evaluate the energy consumption and network lifetime of a UAV-assisted WSN under two different use cases: (1) the UAV is used as relay node; and (2) the UAV is used as mobile sink. In Use Case 1, the network lifetime is more than five times longer than in Use Case 2. Using a UAV as a relay node preserves the network energy for a longer period, regardless of the flying distance of the UAV. In our experiment, three different percentages of distance from the remote Base-Station to the Cluster-Head were involved. If a UAV is flying on 50% distance, the average energy per node expires very quickly. If the distance percentage is at 10%, the average energy per node drops at a much slower rate.
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