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Essay: Comparison of LEACH and PEGASIS Hierarchical Routing Protocols in Wireless Sensor Networks

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Abstract’The efficiency of wireless sensor network largely depends on the routing protocol used. Routing is a major challenge for sensor networks as it presents a trade-off between responsiveness and efficiency. Hierarchical class of routing protocols introduces a structure on the network to achieve stability, energy efficiency and scalability. There are various protocols existing in this category. In this paper, we analyse Low Energy Adaptive Clustering Hierarchy (LEACH) and Power Efficient GAthering in Sensor Information System (PEGASIS) hierarchical protocols. This work analyzes these protocols on the basis of total enery consumed, overheads, and sensors lifetime and provides a comparison of LEACH and PEGASIS with simulation results.
Index Terms’WSN, LEACH, PEGASIS, Sensoria simulator
With the advancement of technology in communication and electronic components, there is an easy availability of cheap and tiny microprocessors which are connected via a wireless network. A wireless sensor network (WSN) is composed of low power sensor source nodes, a set of resources for computation at center to handle data aggregation and a sink node where all the information gets accumulated in the end. Wireless sensor networks are used in a wide variety of applications for monitoring. The applications are: environmental, health, military, home and industry automation etc. Routing is a method of finding out a path between the source and the destination node. In WSNs, the network layer is used to apply the routing and routing protocol is a key aspect in the design of establishing a communication link. It requires high reliability for routing protocols when it comes to sensor networks [1]. The network has to be robust so that there are multiple paths available to transmit the data from source node to the destination node. The sensor nodes have limited energy and also the recharging of sensor nodes is usually impractical due to their mobility. Thus, limited energy is an essential design issue in wireless sensor networks. In case of sensor networks, the focus of the network protocols is on low power consumption in order to increase the lifetime of the network [5].
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In hierarchical routing, few nodes are given a higher priority as compared to others. For example, the nodes may be divided into clusters and each cluster is assigned a cluster head. These cluster heads are responsible for the data processing of the whole cluster.
A. Low Energy Adaptive Clustering Hierarchy (LEACH)
Low-energy adaptive clustering hierarchy (LEACH) is a routing protocol in which the data is delivered to the data sink or base station in a cluster-based approach. There are few factors to be kept in mind such as maximizing network lifetime, minimizing energy consumption and performing data processing at intermediate nodes to reduce the number of transmissions. It is a cluster-based hierarchy in which the entire network is divided into clusters and each cluster has a cluster-head assigned to it. Cluster formation is dynamic in each round and the cluster head is responsible for the data collection from all the nodes of that cluster; it processes the data and sends the collected data to the base station. In LEACH, cluster-heads are selected randomly but the energy spent for each round is balanced as all the sensor nodes have a probability to be selected as a cluster-head. For every round, 5% of the total sensor nodes are cluster-heads [6].
The advantage is that it avoids data redundancy at the sink/base station. But there is no peer to peer communication amongst the nodes of the cluster. Fig. 1a) shows the connectivity of sensor nodes in LEACH protocol [6].
B. Power Efficient GAthering in Sensor Information System (PEGASIS)
Power-efficient gathering in sensor information systems is a routing protocol in which a chain based approach is followed. This protocol follows a greedy algorithm starting from the farthest node and all the sensor nodes form a chain like structure. It works on the principle that each node will transmit to and receive from its close neighbors. There is a leader in the chain which is responsible for transmission of the combined data to the sink node [4]. Nodes take turns being the leader in the network which evenly distributes the energy load amongst the nodes. This even energy distribution and high energy efficiency leads to the extension of the network lifetime. It attempts to reduce the delay that the data acquires on the way to the base station [6]. Fig. 1b) shows the connectivity of sensor nodes in PEGASIS protocol [4].
Figure 1. Connections between nodes and base station for a) LEACH and b) PEGASIS
II. Comparison between LEACH and PEGASIS
This segment illustrates a theoretical comparison of the two routing protocols ‘ LEACH and PEGASIS. Both the routing protocols fall under hierarchical category, i.e., few nodes are given priority over the others. In LEACH, local data processing occurs at specified nodes called cluster-heads and finally aggregated data is transmitted to the sink node. While in PEGASIS, no data aggregation occurs. LEACH is cluster-based hierarchy while PEGASIS is a chain-based approach. When we check the network lifetime, PEGASIS offers extended lifetime of the network as there is a balance in energy distribution. The number of node deaths in PEGASIS is lesser as compared to LEACH. Table I briefs about a comparison of LEACH and PEGASIS on the basis of various parameters.
Table I. Comparative Table for LEACH and PEGASIS
Type of protocol Hierarchical Hierarchical
Network Lifetime High Very high
Data Aggregation Yes No
Power Consumption High Maximum
Overhead High Low
Data Delivery Model Cluster-based Chain-based
QoS No No
Specified path Yes Yes
Scalable Yes Yes
Query Based No No
III. Network Configuration and Results
A sensor network was with created with 50 nodes and above said routing protocols were compared using SENSORIA ‘ a Graphical User Interface (GUI) based simulator [2]. The number of nodes was varied for each simulation from 50-400. The performance of the routing protocols- LEACH and PEGASIS is analyzed in terms of communication overhead, total energy consumption and the network lifetime. The details of simulation setup are given below in Table 2.
Table II. Simulation parameters and values
Parameters Values
Number of nodes 50-400 (Variable)
Energy / node 0.5 J (Homogenous)
Simulation area 40m X 40m
Transmission range of each node 70m
Sensing range (each node) 8m
Location of base station At origin (0m X 0m)
Data packet 2000 bits
Control packet 248 bits
Data transmission speed 100 bits/sec.
Bandwidth 5000 bits/sec.
Fig. 2 shows the connectivity of the nodes in the Sensoria simulator in the simulation area of 40m X 40m where the nodes are distributed randomly.
Figure 2. Network connectivity graphs in Sensoria for a) LEACH and b) PEGASIS
B. Comparison of LEACH and PEGASIS
This section presents a comparison of LEACH and PEGASIS based on simulation.
In the case of LEACH protocol, the communication overhead (in terms of route energy in joules) increases with an increase in the number of nodes deployed in the network as shown in Fig. 3. The overhead thus becomes significant and affects the energy consumption, security, communication stability and the quality of service in large networks with LEACH protocol. On the other hand, the overheads are very small, almost negligible, in the case of PEGASIS protocol and as a result it does not affect other network characteristics. Thus, PEGASIS outperforms the LEACH protocol in terms of communication overhead for dynamic cluster formation.
Figure 3. Plot for Number of Nodes and Communication Overhead for LEACH and PEGASIS
Fig. 4 shows the plot for the total network energy (in joules) for both LEACH and PEGASIS routing protocols for different number of sensor nodes. The simulation result shows that PEGASIS has almost constant consumption of the energy with time for a specific network size while for LEACH it decreases. When the number of nodes increases in the network the energy consumption increases.
Figure 4. Plot for Total Energy of the Network for different number of nodes
The simulations are done to find out the number of rounds of communication for LEACH and PEGASIS protocols when we set a certain percentage of sensor nodes death. The results from Fig. 5a) show that PEGASIS has higher network lifetime as compared to LEACH and it increases with the increase the percentage of nodes death.
As shown in the Fig. 5b), PEGASIS achieves around 2x the number of rounds compared to LEACH at all values of number of nodes deployed in the network. This shows that as compared to LEACH, PEGASIS offers better stability and lifetime in large networks.
Figure 5. Plot for a) Percentage of Sensor Node Death with Number of Simulation Rounds b) Number of Nodes vs. Number of Rounds
In this paper, a comparison of two hierarchical routing protocols ‘ LEACH and PEGASIS is presented. Our analysis shows that PEGASIS performs better than LEACH in terms of network lifetime, communication overhead and the percentage of node deaths. PEGASIS also offers an extended lifetime of the network because of the energy efficiency. For large networks, the early death of the nodes reduces the network stability in LEACH as compared to PEGASIS.
We would like to thank G. Al.-Mashaqbeh for providing us the permission and guidance to install and understand SENSORIA simulator.
[1] J. N. Al-karaki , Ahmed E. Kamal, ‘Routing Techniques in Wireless Sensor Networks: A Survey,’ IEEE Wireless Communications, December 2004
[2] J. N. Al-Karaki and G. Al-Mashaqbeh, ‘SENSORIA: A New Simulation Platform for Wireless Sensor Networks,’ International conference on Sensor Technologies and Applications, SensorComm. pp: 424 ‘ 429. 2007.
[3] Laiali Almazaydeh, Eman Abdelfattah, Manal Al- Bzoor, and Amer Al- Rahayfeh, ‘Performance Evaluation of Routing Protocols in Wireless Sensor Networks,’ International Journal of Computer Science and Information Technology, Volume 2, Number 2, April 2010
[4] S. Lindsey, and C. Raghavendra, ‘PEGASIS:Power- efficient gathering in sensor information systems,’ IEEE Aerospace Conference Proceedings,2002, pp.1125-1130.
[5] K. Akkaya and M. Younis, ‘A Survey on Routing Protocols for Wireless Sensor Networks,’ Elsevier Ad Hoc Network Journal, Vol. 3, pp. 325-349, 2005.
[6] Sohrabi K, Daniel Minoli and Taieb Znati. Wireless Sensor Networks : Technology,Protocols and Applications. Wiley and sons Publication. 2007.
[7] M. Younis, M. Youssef and K. Arisha, ‘Energy-Aware Routing in Cluster-Based Sensor Networks,’ in the Proceedings of the 10th IEEE/ACM(MASCOTS2002), Fort Worth, TX, October 2002.

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