Mobile target tracking is one of the most important applications of wireless sensor networks (WSNs). But, the use of sensor networks for object tracking faces a number of issues in which the limited energy supply is the most important. So in target tracking problem, using methods to decrease the energy consumption as well as high accuracy and quality of tracking is the main goal. Hence, reducing the number of participant nodes in tracking phase, increasing the sleep duration of noninvolved nodes and decreasing the number of transmitted packets to the sink are the most referred methods. In this chapter the authors introduce the most suitable methods for energy efficient mobile object tracking.
TopIntroduction
Rapid advances in miniaturization in computing and sensor technologies and advent of low-power short-range radios recently have given rise to strong interest in smart sensor networks (Tyagi & Kumar; Safa El-Hajj, & Zoubian; Tadayon, Khoshroo, Askari, Wang, & Michel, 2013; Kuk Liu, & Liu, 2011).Each sensor node has capability of sensing the environment, processing data and communicating with the base station. All these tasks are done without human involvement and this makes such networks have a lot of applications in both military and civilian fields(Rezaii, 2011; Pathan & Hong, 2008).
Target tracking is one of the most important and useful application of WSNs. In the early dawn of the research area, the main driving force was military applications, such as detecting and tracking enemy vehicles and soldiers and estimating the positions, speeds and directions of incoming aircrafts. However, as the field has developed and matured, the methods have spread to disparate domains, such as bio-medicine, finance, wild animal habit monitoring, civilian scenarios, air traffic control and so forth (Pathan et al., 2008).
The foundation of tracking is to recursively estimate the position of considered mobile object in each moment. In fact a target tracking system is often required to ensure continuous monitoring and estimate the trajectory (Daniel Svensson., 2007). In WSN thousands of sensor nodes are deployed and used to find mobile objects position which is a complicated scenario and is accompanied with collaborative works between nodes. They should sense the environment, detect intruding objects which are within the sensing range of them, collect data, process data and send information to the base station. So there should always exist nodes that can detect the target along its trajectory, with low detection delay or high coverage level, and base stations can always receive the latest reports about the target in a timely manner.
Sometimes sensor nodes are to identify and track one or more individual objects, such as people, animals, and vehicles. The individual objects usually have very small size comparing with the large area with sensor network deployed. There are some large objects, such as diffused poison gas, biochemical, and chemical liquid, spreading in very large region with sensor network deployed (Shih, Wang, Chen, & Yang, 2008). Detection and tracking this type of objects usually done different from individual ones and we do not consider them in this chapter.
The use of sensor networks for object tracking faces a number of main issues. These issues contain limited energy supply and communication bandwidth, distributed algorithms and control, and handling the fundamental performance limits of sensor nodes, especially as the size of the network becomes large. (Monowar, Alam, Obaidur Rahman, Hong, & Lee, 2010; Martirosyan, Boukerche, Richard, & Pazzi, 2008.)
Tracking of the mobile objects should solve main problems such as object detection, localization, and prediction. As mentioned above, in the localization problem, excessive sensors may join in detection and tracking for only a few objects. And, if all nodes have to always wake up to detect a mobile target, there are a lot of waste of battery power and channel utilization. Also if each sensor node sends packets directly to the sink, it consumes a lot of energy. Actually, power conservation is one of the most critical issues in target tracking since it would be difficult to replace the battery of the sensor nodes that are once deployed in the network area (Pathan et al., 2008). So we can say that energy consumption is the most important design factor for WSN target tracking systems.