Vicky Pandhare #1, Shankar Bhoskar*2, Partik Ughade#3 , Prof. R. V. Bobate#4
#1,2,3Students E & C Engineering, PIET, RTMNU, India
#4Assistant Professor E & C Engineering, PIET, RTMNU, India
Wireless sensor network consists of sensor nodes which are powered by battery; to communicate with each other for environment monitoring. Energy efficiency is the main issue in wireless sensor networks. Therefore, to maximize network lifetime and achieve maximum reliability and scalability, routing techniques have been developed. LEACH is the conventional hierarchical clustering protocol widely used in WSNs. This paper reviews the taxonomy of WSN routing protocols and also highlights issues in LEACH protocol along with disadvantages. The objective of this paper is to provide brief detail of some LEACH improved versions. Finally this paper compares some features of LEACH protocol variants.
Keywords—Wireless Sensor Network (WSN), Clustering, LEACH (Low Energy Adaptive Clustering Hierarchy) Routing Protocols.
Wireless Sensor Networks (WSNs) is considered as one of the most powerful technologies in 21st century. Recent advancement in Micro-electronic-mechanical-systems (MEMS) and wireless communication system, tiny, cheap and smart sensor nodes collaborated with wireless links and the internet deployed in physical area which provide many opportunities in various applications, for example battle field surveillance, environment monitoring, and health care applications.
Wireless Sensor Network is a special kind of non-infrastructure networks capable of wireless communication having large number of low-cost sensor nodes with limited power and multi-functional capability. A typical sensor node includes four basic components: a sensing unit, a processing unit, a communication unit, and a power unit as in figure(1).
WSNs are not centralized one as no static infrastructure exists. Peer-to-peer communication exists between nodes. Multi- hopping can cause a sensor node to communicate with a node that is not in radio range of each other via intermediate nodes. So WSN provides flexibility of adding or removing nodes in the network. The network can be divided into no. of clusters called clustering. In each cluster, one of the sensor nodes is elected as Cluster Head (CH) and the rest of the nodes act as Cluster Members (CM). All sensor nodes work in cooperation within each cluster to serve the request. Cluster head collects the data from its members and data aggregation is done by each cluster head to remove data redundancy and forwarded to the sink. As cluster head consumes more energy than cluster members, the workload of cluster heads is distributed among all nodes in wireless sensor network by rotating their roles to equalize energy consumption called Cluster Head rotation.
Energy consumption is an important issue in WSN because sensor nodes are battery operated and cannot function without enough power level. The ever changing network topology and limited power-supply nodes make WSN quite challenging and become a popular research area.
1.1 Characteristics of WSNs
Unlike traditional wireless sensor networks like MANETs, WSN has unique characteristics as follows:
Dynamic Network Topology: Network topology changes frequently as nodes can be added or removed, node failure, energy depletion, or channel fading.
Application Specific: The design requirement of the network varies with required application..
1.1.3 Energy constrained: Nodes are portable and are highly limited in energy, computation and storage capacities. This is the most important design consideration of WSN.
1.1.4 Self-configurable: Nodes are randomly deployed without careful planning. Once deployed, nodes have to configure autonomously themselves into a communication network.
1.2 WSN ROUTING PROTOCOLS
To optimize energy consumption in the network is to implement routing protocols defining set of rules specifying how message packets transfer from source to destination in a network efficiently and with less amount of energy consumed. Figure 2 shows the classification of routing protocols in WSNs.
1.2 TYPES OF CLUSTERING ALGORITHMS
- Event-to-Sink Directed
- Load balanced clustering scheme
- K-means algorithm
- Low-Energy Adaptive Clustering
- Hybrid Energy-Efficient Distributed clustering
- Energy Efficient Hierarchical Clustering
- Weight-Based Clustering Protocols.
II. CLUSTERED-BASED HIERARCHICAL ROUTING PROTOCOLS: OVERVIEW
Low-Energy Adaptive Clustering Hierarchy (LEACH), proposed by Heinzelmanetal., is a typical hierarchical clustering routing protocol, which adopts distributed clustering algorithm where cluster-head rotation mechanism, data aggregation, and data fusion technologies effectively improves the lifetime of network. In order to optimize energy in the network, nodes are selected as cluster head circularly and randomly. The normal nodes called cluster members join the corresponding cluster head nodes on the basis of principle of proximity. Normal nodes sense data and send directly to the cluster head nodes. The cluster head nodes receive sensed data, aggregate the data to remove redundancy and fusion processes are carried out and data is send to the sink (or Base Station). So LEACH increases network lifetime by decreasing network energy consumption, and reducing number of communication messages by data aggregation and fusion.
The process of formation of clusters in LEACH is shown in figure 3.
In order to achieve the design goal the key tasks performed by Leach are as follows :
- Randomized rotation of the cluster heads and the corresponding clusters.
- Global communication reduction by the local compression.
- Localized co-ordination and control for cluster setup and operation.
- Low energy media access control.
- Application specific data processing.
2.1 Hierarchical Routing Protocol
This routing protocol plays an important role in scalability and stability of network. In hierarchical structure higher energy nodes are used to aggregate and send the information whereas low energy nodes are used to sense the data. This is an energy efficient routing protocol which improves network lifetime.
Example- LEACH, TEEN, A.PTEEN.
2.2 LEACH (Low Energy Adaptive Clustering Hierarchy)
This protocol uses the radio model to estimate energy consumption in transmission of data. Leach consists of large number of associate nodes along with a cluster head. The responsibility of a cluster head is to congregate the data from member node ,compress and transmit it to the base station. Every node is provided with a time slot to respond in order to prevent collision.
III. LEACH Model
LEACH is one of the energy efficient hierarchical routing protocols. This routing protocol uses a clustering method to transmit data in order to obtain advantage on reduction of energy consumption. In this method sensors are gathered into a disjoint set known as cluster and one of the sensor node acts as the head of a cluster, which communicates compressed information to the base station. Nodes that are not cluster head only communicate with the cluster head in a TDMA fashion, according to the schedule created by the cluster head.
III.I Comparison of LEACH and its Modified LEACH Protocols
Every protocol has some limitations along with the benefits. To improve the functioning of protocols we need to study the comparison between these protocols, and further modify them for better result.
a. V LEACH :
Working of v leach protocol is similar to LEACH protocol. According to LEACH protocol CH is the node which is responsible for sending and receiving of data to base station. So energy dissipation is most in CH rather than the member node. This could lead to death of a CH and network to stop working. To prevent this V LEACH protocol consists of a vice CH along with a CH. So that when the CH dies, vice CH will take over the role of CH so the network performance is not affected.
b. TL LEACH:
This is two level leach protocol used to reduce the energy dissipation by cluster head situated far away from base station. As we know transmission requires energy and if it is far away it will require more energy and CH will die soon. So in this protocol the processed data is transmitted to other CH which is located in between the path of CH and Base station. Thus reducing the burden of transmitting data through single CH. It works as a relay station and helps in reducing energy consumption of CH.
c. MULTI HOP LEACH MULTI HOP LEACH:
Is similar to LEACH protocol but communication path from cluster head to base station is converted from single hop to multi hop. Data is transmitted to base station through various cluster head .It transfers data from one cluster head to corresponding cluster head which is nearest to base station. It selects optimal path with lesser number of hop count between first cluster head and base station. In this type of LEACH protocol energy is efficiently used by network because far away cluster head require low energy for sending data than nearer cluster head. This reduces the energy dissipation of single CH if it is situated far away from base station. Thus increasing the life span of network.
d. S LEACH:
Solar-Aware Low Energy Adaptive Clustering Hierarchy The goal of inventing S LEACH is to extend the lifetime of the sensor nodes and thus increasing the stability of network. Solar powered sensor nodes are chosen for intensive task by cluster head. This protocol is used to enhance energy of the isolated sensor nodes using solar power. As these sensor nodes are used in battlefield,
Search and rescue operation in remote areas where replacement of batteries is not feasible. To overcome this limitation S LEACH was proposed in which some nodes are provided with solar power and these nodes acts as cluster head. Selection of cluster head is on the basis of solar power along with the energy present within the sensor nodes.
e. Solar Aware Centralized LEACH:
This routing protocol uses centralized algorithm for the selection of cluster head , it is selected by base station. Selection of a cluster head is on the basis of solar power, nodes transmit their solar status along with energy possessed by them . Base station selects a node with higher solar power as cluster head.
f. PEGASIS (Power Efficient Gathering in Sensor Information System):
This is an improvised version of LEACH protocol. In PEGASIS protocol clusters are not formed instead every node communicate to its nearest node to transmit and receive the data and among them one node is selected to communicate with the base station. This chain formation is Performed in a greedy way to improve the network life span by reducing overhead energy dissipation and bandwidth usage.
g. TEEN (Threshold Sensitive Energy Efficient Sensor Network Protocol):
It is one of the hierarchical clustering protocol in which hierarchy of sensor nodes is present. In this protocol data is accumulated from sensor nodes and transmitted from cluster head of first level to cluster head of next level and so on until it reaches to the base station. TEEN executes its function on the basis of a threshold value. It is the best energy efficient protocol as it implies a constraint on when the sensor should transmit the data thus reducing number of transmissions.
h. APTEEN (Adaptive Threshold Sensitive Energy Efficient Sensor Network Protocol):
It is an enhancement of TEEN protocol in order to overcome its drawbacks. It uses the same concept of TEEN to reduce energy dissipation. This protocol provides a time critical information as well as constant transmission of sensed data to user. It works on the combination rule from both the LEACH and TEEN protocol. Its efficiency is between the two protocols as it performs the function of both the protocol.
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In this paper we have described about various energy efficient routing protocols in wireless network. Among them LEACH is one of the important routing protocol which reduces energy dissipation and increases network lifetime with the help of clustering technique. We have discussed about some modified versions of LEACH and analyze that each routing protocol addresses specific problem and tries to improve prevalent clustering routing protocol LEACH. Further improvement in energy efficiency is possible in routing protocols by improving cluster head selection techniques.
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