Key Words: Hybrid wireless sensor networks, battery powered and energy harvesting sensor nodes, node placement
SUMMARY & CO CLUSIO SSensor nodes in wireless sensor networks (WSNs) are usually battery-powered sensor nodes (BPSNs) and can rarely meet design goals such as network lifetime, energy and reliability. Energy-harvesting sensor nodes (EHSNs) are an alternative type of sensor nodes, which are capable of converting different types of energy to electrical energy. They have longer lifetime but higher cost than BPSNs. Combining BPSNs and EHSNs in a heterogeneous WSN has the potential to deal with the conflicting design goals. In addition, consider certain scenarios where replacing batteries of BPSNs is impossible, EHSNs can be deployed instead to satisfy the quality of service (QoS) of applications running on the hybrid WSN. In this work, we study a hybrid WSN including both types of sensor nodes to deal with the network reliability and cost requirements, particularly, the limited lifetime of BPSNs and high cost of EHSNs. The problem is to find the optimal locations for a specific number of EHSNs in the hybrid WSN with the objective to provide the best combination of average path reliability, implementation path cost, and average energy consumption based on the QoS requirements.Both the centrality concept and the multivariable nonlinear programming method are explored to find the optimal positions for EHSNs in the hybrid WSN.
I TRODUCTIOWireless sensor networks (WSNs) bring significant advantages over traditional communications in today's applications such as environmental monitoring, structure monitoring, homeland security, health care and etc. Many important factors like energy consumption, implementation cost, and reliability can affect the design of WSNs [1][2][3][4].Sensor nodes in WSNs are usually battery-powered sensor nodes (BPSNs) and can rarely meet design goals such as network lifetime, energy and reliability. For example, BPSNs typically optimize their energy usage via decreasing their sampling frequency or duty-cycle so as to maximize their lifetime, which however can decrease the sensing reliability of the WSN.Extensive research has been performed to maximize the lifetime of BPSNs [5,6]. Examples include energy-aware MAC protocols [7-9] and system architectures [10-12], as well as energy-conservation by scheduling sleep intervals for some nodes [13]. Most of these techniques try to optimize energy usage to maximize the lifetime of a sensor node. However, with BPSNs, it is difficult to optimize all the performance parameters at the same time. For example, implementation cost will be increased using higher battery capacity, increasing transmission range causes higher energy requirement, decreasing transmission range implies more hops in the communication path to the sink node resulting in energy usage at more intermediate sensor nodes [5]. Energy-harvesting sensor nodes (EHSNs) are an alternative type of sensor nodes, which are capable of converting different types of energy (e.g., from environment ...