I. INTRODUCTION
In the last few years, more and more researchers have devoted to the Wireless Sensor Networks (WSNs) technology research. And WSNs technology has been made great progress and utilized broadly in different area applications, such as environmental monitoring, power monitoring and factory automation and so on [1]. Due to wireless nodes are distributed randomly or designedly in monitored field for different applications, the initial network topology may not offer a reliable and efficient network communication. Or some network nodes are failure during the operation; place or redeploy some new Relay Nodes (RNs) for ensuring connectivity would be very important so that the WSN becomes reliable and efficient.
Normally, the Sensor Nodes (SNs) and Base-Station Nodes (BSNs) are fixed in specific place in industrial applications, the SNs and BSNs may not be connected or due to power- consuming for long distance communication [2]. In order to solve above issues and ensure SNs and BSNs communication reliability and balance the energy consumption between SNs and BSNs long distance communication, the optimal RNs placement is needed. This paper focuses on optimizing relay nodes placement issues research [2, 3, 4, 5, and 6].