LEACH : Low Energy Adaptive Clustering Hierarchy

LEACH stands for Low Energy Adaptive Clustering Hierarchy. This is a TDMA based protocol for wireless sensor networks with homogeneous nodes. LEACH is self organizing, adaptive clustering protocol. LEACH aims to distribute energy consumption at every node in the sensor network uniformly, aggregate data, i.e. support data fusion and localized coordination, between nodes to form and operate clusters.

All nodes in the network organize themselves into local clusters, with one node in the local cluster acting as cluster head. All nodes communicate only to the cluster head, and the cluster head conveys data to the base station. Nodes with higher capability advertise themselves as cluster heads, other nodes join the cluster head which is nearest to them. As cluster head has to spend lot of energy ,after certain time, randomized rotation of the cluster head is done, so that only node does not drain its energy. Every cluster head will prepare a schedule, to each of its members. The members communicate with the head only during that duration and sleep for the rest of the time. The diagram below shows the architecture of LEACH.



Architecture of LEACH

The operation of LEACH is broken into rounds. Each round starting with setup phase, during which clusters are formed and steady phase during which data is transferred to base station. Steady phase is longer than set up phase. Initially at the beginning of each round, each node decides if it has to be cluster head or not. The node which decides to be cluster head sends broadcasts a message. All other nodes will keep their receiver on and decide to which cluster head they need to join. Every node selects a cluster head which is nearest to it.

All nodes send messages to respective cluster heads. The cluster head based on the number of requesting node creates a TDMA schedule for all the nodes. Only during their respective schedules nodes interact with the cluster head, else the nodes will sleep.The cluster heads receives data form all nodes in its cluster, aggregates the data and sends it to the base station. The phase after the schedule is announced, is the steady phase and phase before schedule is announced, is setup phase. This can be seen in the diagram below. After the steady phase next round starts.



States in operation of LEACH

To avoid interference between clusters, all nodes in a cluster communicate using a CDMA code selected by the cluster head. There can also be hierarchy of clusters.