Modified leach protocol in wireless sensor network a survey

Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
1
MODIFIED LEACH PROTOCOL IN WIRELESS SENSOR
NETWORK–A SURVEY
Chinchu T Sony1
, Sangeeta C P2
, C D Suriyakala3
1
Dept., of ECE, TIST, Cochin, India
2
Dept., of ECE, TIST, Cochin, India
3
Dept., of ECE, SNGCE, Cochin, India
ABSTRACT
Advances in wireless technology, digital electronics, and MEMS (Micro-Electro Mechanical-Systems) have
enabled the deployment of large scale wireless sensor networks (WSN). The main problem in WSN is limited battery
life. So the efficient use of available battery power is one of the major factors to be considered. Studies on WSNs shows
that cluster based network architecture is the most energy efficient approach when compared with direct transmission and
multipath technique. From the different cluster based protocol, LEACH (Low Energy Adaptive Clustering Hierarchy)
shows the better performance in terms of energy consumption. We can make the LEACH network much more efficient
by reducing the energy usage during Cluster Head selection procedure, and communication between far away nodes to
base station. In this work, modified LEACH protocol is surveyed and analyzed their performance based on the metric,
residual energy.
Keywords: Cluster, Cluster Head, LEACH, Multihop, WSN;
1. INTRODUCTION
Wireless sensor networks are highly distributed networks of small, lightweight wireless nodes communicate
over a short range. These are deployed in large number to monitor the environment or the system by measuring the
physical parameters such as temperature, pressure, humidity etc. Each sensor nodes consist of three subsystems: the
sensor subsystem which senses the environment, the processing subsystem which perform local computation on the
sensed data and the communication subsystem responsible for exchange information with neighbor nodes. Networking
individual sensor to a large number leads to wider range, which cause robust and reliable. Two main operation carried
out in WSN are data dissemination and data aggregation. Data dissemination is spreading of data in whole network and
data aggregation is collection of data from several nodes by sink.
Sensor network consist of different types of sensors like seismic, thermal, visual and infrared and able to
monitor a wide variety of ambient conditions: temperature, pressure, humidity, soil makeup, vehicular movement, noise
levels, lighting conditions, the presence or absence of certain kinds of objects, mechanical stress levels on attached
objects and so on. These increases the application of sensor networks in battle fields, identification of contaminated
environments, environmental monitoring, analysis of structural conditions of buildings, Roads and highways in
intelligent applications in medicine etc.
Sensors are usually relying on battery for power which in most cases cannot recharge or replaced. Due to the
limited battery power, energy consumption is the most critical issues in wireless sensor networks which in turn effect the
INTERNATIONAL JOURNAL OF ELECTRONICS AND
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Volume 5, Issue 12, December (2014), pp. 01-05
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lifetime of network. Conventional routing protocols used in WSN are directly communication with Base Station (BS) and
Minimum Transmission Energy (MTE). Both protocols the energy of node will drain out quickly [1]. Therefore most
energy efficient scheme, clustering of nodes is used to increase the life span of the network. Use of clustering results in
has small transmission distance from nodes. Cluster based architecture organizes the sensor nodes into clusters each
cluster have a cluster head (CH) and cluster members (CM). The CMs in each cluster are involved in message exchange
with their respective CH and BS will gathered data from CHs. The fundamental and most popular cluster based routing
protocol is Low Energy Adaptive Clustering Hierarchy (LEACH) which is discussed in section II, improvement in
LEACH protocol for different issues are in section III and the survey is concluded in section IV.
2. LEACH PROTOCOL
Low Energy Adaptive Cluster Hierarchy (LEACH) is the fundamental and most commonly used cluster based
routing protocol. The main advantage of this protocol is improved the lifetime of WSN by reducing energy consumption.
Even distribution of energy among the nodes in the network and performing data aggregation are the main features of
LEACH. Some assumption to be considered in LEACH are the BS is fixed and located far from the sensors,
homogenous sensor nodes in the network and have limited energy source. As LEACH is a cluster based protocol it
organize the nodes into clusters which helps to distribute the energy among the sensor nodes in the network. Each cluster
has a Cluster Head and non-cluster head nodes as shown in Fig (1).
LEACH randomly selects nodes as Cluster Heads and performs periodic reelection, so that high energy
dissipation experienced by the CH in communication with the BS is spread across all the nodes of the network. Each
iteration of CH selection is called a round. The operation of LEACH based on several rounds. Each round consists of
setup phase and steady state phase
Figure 1: Cluster formation in LEACH[4]
2.1. Setup Phase
In setup phase, cluster formation and Cluster Head selection takes place. For Cluster Head selection every node
chooses a random number between 0 and 1 and a threshold value T (n) is evaluate as in (1):
ܶሺ݊ሻ = ቊ
௣
ଵି௣∗௥௠௢ௗଵ
௣ൗ
; if nεG
0 ; otherwise
(1)
Where p - desired percentage of CHs, r- current round and G - set of nodes that have not been CHs in the
last 1/P rounds. Nodes that are CHs in round 0 cannot be CHs again in the next 1/P rounds. Using this thresholdT(n),
each node will be a cluster-head at some point within 1/P rounds. If the random number is less than a threshold value
T(n) node become the Cluster Head.(CH). During round 0 (r=0), each node has a probability P of becoming a cluster-
head. The nodes that are cluster-heads in round 0 cannot be cluster-heads for the next 1/P rounds. Thus the probability
that the remaining nodes are cluster-heads must be increased, since there are fewer nodes that are eligible to become
cluster-heads. After 1/P -1 rounds, T(n)=1 for any nodes that have not yet been cluster-heads, and after rounds, all nodes
are once again eligible to become cluster-heads.
After CH selection, each CH advertises its selection to the rest of the nodes by using the CSMA/CA protocol.
After that each node selects a CH based on the Received Signal Strength Indication (RSSI) of the advertisement. Each

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node uses CSMA/CA protocol to transmit its selection. During that, all CHs must keep their receivers ON. Then when
clusters are formed, each CH creates a TDMA schedule according to the number of nodes in the cluster. Each node sends
their sensed data to its CH during its allocated transmission time in the TDMA. During the steady state phase, each
sensor node senses and transmits data to its CH based on the TDMA schedule. The CHs receive all the data and
aggregate it before being sent to the BS. After a certain time, which is determined a priori, the network starts another
round by going back to the setup and steady state phases again.
Figure 3: Timing diagram of round [1]
2.2. Steady State
During the steady state phase, each sensor node senses and transmits data to its CH based on the TDMA
schedule. The steady state operation is broken into frames, where nodes send data to their CH at most once per frame
during allocated transmission slot. The CHs receive all the data and aggregate it before being sent to the BS. After a
certain time, the network starts another round by going back to the setup and steady state phases again.
3. MODIFICATION ON LEACH
LEACH is an energy efficient protocol works on multiple clusters. Only Cluster Head will communicate with
the Base Station. Cluster Head selection procedure, idle listening and overhead in CH, far distance from BS will reduce
energy efficiency of the protocol. To overcome these issues so many improvements on LEACH are done.
Sensor nodes far away from their cluster-heads or cluster heads far away from the base station will spend more
energy for longer distance transmission. As a result, the remaining energy level for each node in the network will be
unbalanced. An optimal energy adaptive clustering algorithm has been developed in [2]. For nodes having higher
residual energy than the average energy of the whole network are continued to select cluster head. Otherwise there can be
high probability to exhaust all their rest energy for data transmission and become dead nodes[2].Selecta Super Cluster
Head (SCH) responsible for routing the gathered data to the BS. SCH are taken from Cluster Head that should be at an
optimum distance and energy from the BS. This node will act as an intermediate between cluster head and BS[3]. Relay
nodes was chosen from the CHs based on residual energy and the distance to the BS. In set-up phase, they improved the
threshold value to ensure node has high residual energy. After the cluster formation relay node is selected based on
residual energy and distance to the BS. Therefore instead of direct transmission from distant BS and CH can use relay
node as the intermediate node between BS and CH. Here number of CHs in the network should not be too large or too
small which will cause reduction of energy in the networks. So CH should be optimal [4].Thus there will reduction in
energy consumption for larger communication distance. Simulation in [4] shows that LEACH-R saves 20 % energy than
LEACH(Fig 3).
Figure 3: network lifetime[4]
In the LEACH, the CH is always on for receiving data from cluster members, sometimes CH dies earlier
than the other nodes in the cluster because of its operation of receiving, sending and overhearing. When the CH die,
the cluster will become useless because the data gathered by cluster nodes will never reach the base station. Besides
transmitting data directly from CH to base station, CH sends data to the other cluster head which is inside a pre-

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defined radius, so that transmitting energy is less dissipated [5].BS selects the upper layer cluster heads to act as super
cluster heads for lower layer cluster heads[6]. This protocol reduces the energy consumption of sensor nodes by
adaptively increasing the clustering hierarchy. It uses the concept of equal clustering i.e., any node in the given layer will
reach the BS in equal number of hops (Fig 4)[6].
Figure 4: Clustering in different layers [5].
Cluster head selection procedure will increase the energy consumption; if the selected Cluster Head has less
energy than average network energy then Cluster Head will die quickly which reduce the lifetime. Modification in cluster
head selection method can makes energy efficient protocol. By introducing efficient cluster head replacement scheme
and dual transmitting power levels [7] thus life time of node get improved (Fig 5) and also by Choosing the CH based on
remaining energy and distance from the center of gravity [8] will improve the Cluster Head selection method to reduce
energy consumption.
Figure 5: Graph of node dead in LEACH and BEC-LEACH[7]
Cluster heads should be selected based on maximum coverage and should have sufficient energy to prolong the
communication [9] Clusters are dynamically formed and changed with transmission. A QOS aware protocol in [9] is
provided that ensures maximum lifetime of the edges through which routing is performed and thus minimizing the losses
due to node mobility or collision, thereby enhancing the lifetime by minimizing the energy losses. Fig.6 shows that
improved LEACH better performance than LEACH.
Figure 6: Average cluster lifetime and Latency For 25 & 50 nodes[9]

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Uneven clustering can balance the energy consumption of cluster heads by making clusters which are closer to
BS have smaller radius[10], Multi-hop inter-cluster routing mechanism is used to save node energy and BS select an
optimal path from multi-paths for source and sink nodes.BS does everything from broadcasting control packets, routing
paths selection and maintenance. Sensor nodes are only responsible for basic functions, such as sensing data, forwarding
packets on behalf of other nodes and sending sensing data to BS. In [11], developed a Dynamic Cluster Head procedure
and inter-cluster routing selection, which evenly distribute the energy load among all the sensor nodes in the network.
Therefore no overly-utilized sensor nodes, so that nodes energy will not run out quickly before the others. In this Cluster
heads (CHs) which are closer to the base station (BS) have smaller cluster size than those farther from BS [11]. LEACH
is homogenous, so it cannot be used in heterogeneous environment. To overcome this limitation two protocol SEECP and
MEECP were developed [12].
4. CONCLUSION
One of the main challenges in the design of routing protocols for WSNs is how to efficiently use the available
energy, because energy resources are very limited. The main aim while design a routing protocol is to make the nodes
lifetime as long as possible. From our side we concluded that if the improvements on Cluster Head procedure and
multihop technique is included with existing techniques, the sensor network would have been much more energy
efficient. They can reduce the energy consumption thereby increase the life time. In this paper we have surveyed various
LEACH-based protocols and discussed how they reduce energy consumption in WSNs and increase network’s lifetime.
5. ACKNOWLEDGEMENT
We would like to express special thanks to Mr. George M. Jacob, Lab Instructor, Toc H Institute of Science and
Technology. We are also deeply grateful for all those who made it possible to complete this survey successfully.
REFERENCES
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Volume 5, Issue 1, 2014, pp. 148 - 157, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

Modified leach protocol in wireless sensor network a survey

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