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Wireless sensor network (WSN) have become one of the most promising technology in sensing application environment. WSNs environment are able to provide a flexible deployment and maintenance of sensor networks. The sensor nodes can be deployed in highly dynamic environments and hence enable sensor networks to be potentially used in a wide range environment including military applications, security surveillance, environmental monitoring, habitat monitoring, hazard and disaster monitoring and relief operations, healthcare applications (Nematy, Rahmani, Teshnelab, & Rahmani, 2010), home applications as smart home and smart agriculture system (Akyildiz, Su, Sankarasubramaniam, & Cayirci, 2002). The basic goals of WSN generally depend on the application and function including to determine the value of parameter at given location, detect the occurrence events and tracking an object. In an environmental network, sensor nodes can be used to measure the temperature of atmospheric pressure, amount of sunlight and humidity. Sensor nodes also used to detect a vehicle moving through an intersection and estimate the speed and direction of the vehicle. In a military sensor network, sensor used to track an enemy as it moves through the geographic area covered by the network.
WSN consists a number of sensor nodes and one or more base stations spread across a geographical region of interest. Each sensor node has a wireless communication capability and some level of intelligence for signal processing and networking of the integrated data (Fan & Jin, 2010). In addition, with integration of sensing, computation, and wireless communication, the sensor nodes can sense a physical information from the environment, process the information, and report them to the base stations. As illustrated in Figure 1, the sensor node will sense the target point and link the information to the base station by a group of collaborating sensors via a multi-hop communication. The information is transmit to the outside world via the internet or satellites.
Figure 1. Wireless sensor network environment
In WSN, node placement is the fundamental issue that will affect the performance of the WSN application and operation and closely related to coverage and connectivity. According to Mulligan and Ammari (2010), coverage is usually interpreted as how well a sensor network will monitor the region of interest and as a measure of quality of service (QoS) in WSN environment application. Connectivity can be defined as a connection between sensor nodes that can communicate to transfer the information from the target area to the base station. In addition, it is important to maintain the connectivity in order to have the best sensing coverage area. However, these wireless sensors have several constraints especially in random deployment strategy such as a coverage hole, overlapping and also may cause a connectivity failure which is related to the limited sensing and communication range as well as limited battery capacity. An effective node placement can improve and provide a good coverage and connectivity to cover the region of interest efficiently. In this paper, the node placement strategy for improving network coverage and connectivity in random deployment scheme using virtual force approach is analyzed.
The rest of this paper is organized as follows. We address several problems in random deployment such as coverage hole, overlapping and connectivity failure in an issues in random deployment section. In mobile sensor section, we discuss an alternative approach by using mobile sensor to enhance the coverage and connectivity strategy in wireless sensor network. Node placement strategies using Virtual Force Algorithm (VFA) are analyzed and presented in the later section. The simulation results section illustrate the VFA approach in random deployment in order to find an optimal node placement. Finally, the paper is ended with conclusion section.