Clustering the wireless sensor networks by using LEACH algorithm

Each sensor in wireless sensor networks is called a node. Each node can cover a limit or range of its surrounding environment. Thus, each node cannot directly transfer data to base station and can only do it to a short range. Neighboring nodes should be used to transfer data. Since some nodes are placed in the path of data transfer, their energy is significantly used and thus their lifetime decreases. As a result, the network may be divided into several different parts. Meanwhile, there is another solution to transfer data with less expense. In this method that is called clustering, a group of nodes is considered as a cluster and a cluster head is set for each cluster. In this type of clustering, thenodes inside the cluster are only related to cluster head, so that the energy of nodes is saved and the stability of network increases. One of the different types of clustering algorithm is LEACH clustering algorithm that will be discussed in this article. This algorithm reduces the energy consumption of sensor network and increases the lifetime of each node by doing clustering operations 1. Introduction Wireless sensor networks are composed of many nodes (that may reach to thousands of nodes). Each node is called a sensor that can feel a special parameter of environment (temperature, moisture, pressure and etc.) and send it to its neighbors. In other words, the two main features of these sensors are to feel a specific parameter of environment and the ability to communicate or establish relations. Although, in some functions, these nodes may be connected to each other by a cable, in most cases a sensor network is totally wireless. Nodes in these networks are mainly fixed or have a very limited movement. There is usually a central or base node called base station to which all nodes can be directly connected. [13] But in most cases, not all nodes can be directly connected to basestation. For this reason, all nodes need to know a path toward the base node. The history of sensor networks goes back to the cold war period (the early 1950s) and SOSUS system. [2] This system was embedded by the U.S.A in order to identify and trace the submarines of the Soviet Union in North Pacific Ocean. This network is a wide net ofhydrophones that are connected to each other by a cable and cover the ocean. [3] This system is currently used by NOAA institute to monitor the natural phenomenon in the ocean. Today, wireless sensor networks are widely used due to their special features and different functions. [2] Some functions of these networks are the diagnosis offire in forests, identification of dangerous places for human, evaluation of group movements of animals in an area and so on. [4] Each node has a processor and performs a series of primary processing on the obtained data instead of sending all raw data to base station or a node that is responsible for data processing. Then, it sends the processed data to base station. These data are transferred to base station through a multistage path that has no specific infrastructure and base station can be connected to Task Manager Node by satellite or the Internet. [5]