Wireless Sensor Networks Localization

Introduction

Wireless sensor network (WSN) consists of many sensors deployed in a certain area to monitor or detect an event or some events depending on the application and sensor specifications; sensors can detect temperature, sound, pressure, etc. Wireless sensor networks (WSNs) are composed of hundreds, possibly thousands, of tiny low-cost and smart devices called sensor nodes that are capable of measuring various physical values, this sensors are deployed in large numbers, and they are communicating with each other and organizing themselves in order to cooperatively achieve a desired task It can provide opportunities for monitoring and controlling homes, cities, and the environment. Wireless sensor network can be used in many applications such smart home, precision agriculture, industrial monitoring, environmental/earth monitoring. In addition, WSNs have a broad spectrum of applications in the defense area, generating new capabilities for reconnaissance and surveillance as well as other applications. The main challenges of a WSN design and implementation are power consumption constrain for nodes using batteries, scalability to large scale of deployment, Ability to withstand harsh environmental conditions and Ease of use. An important aspect in most of the sensor networks application is the localization of the individual nodes, localization capability is a highly desirable characteristic of wireless sensor networks in environmental monitoring applications such as bush fire surveillance, water quality monitoring and precision agriculture, and other applications. The measurement data are meaningless without knowing the location from where the data are obtained. Moreover, location estimation may enable a myriad of applications such as intrusion detection, road traffic monitoring, health monitoring, reconnaissance and surveillance. Localization enables the efficient routing: A typical sensor network has large number of nodes which communicate at very short distance (a few meters). The data sensed by a node has to be communicated to the central unit through several other nodes. Thus multi-hop routing is a must. In order to impellent multi-hop routing it is necessary that nodes are of their locality, namely, they know their relative position with respect to their neighbors. Consequently localization becomes very important. Localization provides the power saving: Suppose we have deployed the sensor network for pollution monitoring. Now the neighbor sensor nodes will have data which will not be dramatically different from each other. Thus to save power it makes sense to combine the data from neighboring nodes and then communicate the combined, reduced data set, thereby conserving power (since communication takes lot more power than local processing). In order to do this local data fusion, we will need the location information. Once again localization becomes vital. Localization assists in the applications like target tracking: In this application, we typically need to determine the range, speed and the direction of the target. Sensors are deployed in region which sense the moving target, using which the range, speed and direction of the target may monitored. In order to calculate the global orientation of the target it is necessary that we know the location of the sensor nodes. Once again localization becomes necessary. Localization useful in locating the source of the data: In many applications, an event based sensor network is used. Here, the nodes are normally in sleep mode and when an event occurs (say sudden vibrations take place) the nodes are awakened. The nodes than sense and transmit the data. Such data requires a location stamp and therefore localization becomes necessary. From the previous examples we see that localization is indeed a necessity for sensor networks. Moreover, localization techniques vary depending on applications. Patil, Shaha,Desai and Merchant(2011) showed that in their work .Localization systems can be divided into three distinct components as shown in Figure.1: Distance/angle estimation: This component is responsible for estimating information about the distances and/or angles between two nodes. This information will be used by the other components of the localization system. Position computation: This component is responsible for computing a node’s position based on available information concerning distances/angles and positions of reference nodes, reference nodes are nodes which it is positions is known. Localization algorithm: This is the main component of a localization system. It determines how the available information will be manipulated in order to allow most or all of the nodes of a WSN to estimate their positions.

Figure 1.

Localization systems components