40120140501017

International Journal of Electronics JOURNAL OF ELECTRONICS AND
INTERNATIONAL and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 1, January (2014), © IAEME

COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 5, Issue 1, January (2014), pp. 148-157
© IAEME: www.iaeme.com/ijecet.asp
Journal Impact Factor (2013): 5.8896 (Calculated by GISI)
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IJECET
©IAEME

S-LEACH: A SEQUENTIAL SELECTION APPROACH TO ELECT
CLUSTER HEADS FOR LEACH PROTOCOL
Ankit Thakkar1, Ketan Kotecha2
1

Assistant Professor, CSE Department, Institute of Technology, Nirma University,
Ahmedabad - 382 481, Gujarat, India
2
Director, Institute of Technology, Nirma University, Ahmedabad - 382 481, Gujarat, India

ABSTRACT
Wireless Sensor Nodes are deployed in the hostile region to help the user by providing data to
the user for the review purpose. These nodes are having limited power as they are battery operated.
Hence, routing protocol used to deliver data to end users must be energy efficient to provide
prolonged network lifetime. In this paper, we have proposed a decentralized clustering scheme based
on sequential selection (S-LEACH) that maintains desired number of cluster heads during each
round until the death of first node. Extensive simulations are carried out to compare our proposed
protocol with three well known protocols - LEACH (Low Energy Adaptive Clustering Hierarchy),
LDCHS (Low Energy Clustering Hierarchy with Deterministic Cluster Head Selection) and
ALEACH (Advanced LEACH). Simulation results show that S-LEACH outperforms to the LEACH,
LDCHS and ALEACH protocols.
Key words: LEACH, Sequential Selection Approach, Energy Efficient Routing, Cluster Head
Selection, Wireless Sensor Network
1. INTRODUCTION
Energy efficiency is an important issue in Wireless Sensor Network (WSN), and steps taken
to do effective communication by reducing number of transmissions affect the network lifetime. Low
Energy Adaptive Clustering Hierarchy (Heinzelman, W. R., Chandrakasan, A., & Balakrishnan,
H. (2000, January)) is one of the energy efficient adaptive clustering protocols and its primary goal
is to save energy. It has also put foundation to enhance network lifetime with clustered based routing
approach (Wang, A., Yang, D., & Sun, D. (2012)). Many cluster based approaches have been
proposed to enhance network lifetime of a WSN which includes but not limited to EECS (Ye, M.,
Li, C., Chen, G., & Wu, J. (2005, April)), EEHC (Kumar, D., Aseri, T. C., & Patel, R. B.
148

International Journal of Electronics and Communication Engineering & Technology (IJECET),

(2009)), VLEACH (Yassein, M. B., A. Al-zou'bi, Khamayseh, Y., & Mardini, W. (2009)),
CVLEACH (Thakkar, A., & Kotecha, K. (2012)), ALEACH (Ali, M. S., Dey, T., & Biswas, R.
(2008, December)), WALEACH (Thakkar, A., & Kotecha, K. (2012)), WCVALEACH (Thakkar,
A., & Kotecha, K. (2012)), EDACH (Kim, K. T., & Youn, H. Y. (2005, January)), REEH
(Sehgal, L., & Choudhary, V. (2011)),TL-LEACH (Loscri, V., Morabito, G., & Marano, S.
(2005, September)), LDCHS(Handy, M. J., Haase, M., & Timmermann, D. (2002)).
In EECS (Ye, M., Li, C., Chen, G., & Wu, J. (2005, April)), author have achieved near
uniform distribution of cluster heads through localized communication with minor overhead. In
EEHC ((Kumar, D., Aseri, T. C., & Patel, R. B. (2009)), authors have used weighted probability to
elect the cluster heads for heterogeneous WSN. CVLEACH (Thakkar, A., & Kotecha, K. (2012))
improves network lifetime by creating non-overlapping cluster regions by utilizing over hearing
capacity of the nodes. ALEACH (Ali, M. S., Dey, T., & Biswas, R. (2008, December)) considers
remaining energy of the nodes to elect cluster heads. WALEACH (Thakkar, A., & Kotecha, K.
(2012)) improves ALEACH by assigning weight factor. In WCVALEACH (Thakkar, A., &
Kotecha, K. (2012)), authors have combined the idea of weight factor with over hearing property of
the nodes to prolong network lifetime. EDACH (Kim, K. T., & Youn, H. Y. (2005, January)),
prolongs network lifetime by assigning more cluster heads in the region farther from the BS. REEH
((Sehgal, L., & Choudhary, V. (2011)), is designed and validated for heterogeneous wireless sensor
network in which residual energy of the node is considered to elect the cluster head. TL-LEACH
(Loscri, V., Morabito, G., & Marano, S. (2005, September)), improves network lifetime by
reducing data transmission distance by creating two levels of cluster heads. LDCHS (Handy, M. J.,
Haase, M., & Timmermann, D. (2002)) improves stochastic approach of LEACH to elect cluster
head by introducing deterministic component.
The protocols discussed above are energy efficient clustering protocols. They are either based
on LEACH protocol or designed separately. LEACH protocol gives optimal performance when 5%
of the total nodes are elected as cluster heads during each round (Heinzelman, W. R.,
Chandrakasan, A., & Balakrishnan, H. (2000, January)). However, LEACH does not ensure that
desired numbers of cluster heads are maintained during each round. The same is also applicable to
LDCHS and ALEACH protocols as they are based on LEACH protocol. In this paper, we have
proposed a new sequential selection approach (S-LEACH) to maintain desired number of cluster
heads during each round to improve network lifetime.
Rest of the paper is organized as follows: LEACH, LDCHS and ALEACH are described in Section
2; System and Energy model are given in Section 3; S-LEACH is discussed in Section 4; Simulation
Strategy and Result Discussion are presented in Section 5 and Concluding remarks are given in
Section 6.
2. LEACH, ALEACH and LDCHS
In LEACH (Heinzelman, W. R., Chandrakasan, A., & Balakrishnan, H. (2000,
January)), authors have proposed energy efficient cluster based routing scheme, in which role of
cluster head (CH) is rotated between nodes to achieve uniform energy depletion through load
balancing. Each sensor node elects itself as a CH with certain probability. This status is informed by
the CH nodes to the other nodes in the network. After getting status message from the CH nodes,
non-CH nodes select one of the CHs as its own cluster head for which minimum energy is required
for communication. CH nodes receive data from the non-CH nodes, fuse it and send to the Base
Station (BS). At the commencement of the each round, a node selects a random number which is
uniformly distributed pseudo random number between 0 and 1. If random number is less than
threshold value T(n) which is given by equation 1, then node elects itself as a CH for the current
149


round. LEACH ensures that each node becomes CH only once every 1/p rounds, where p is the
desired percentage of cluster heads known a priori to the algorithm.

(1)

In ALEACH (Ali, M. S., Dey, T., & Biswas, R. (2008, December)), authors have modified
threshold value T(n) which is given by Equation 2. ALEACH also works in rounds as LEACH. Each
round begins with Cluster Setup phase. During cluster setup phase, a node selects a random number
between 0 and 1. If selected random number is less than threshold value T(n), then the node declares
itself as a cluster head where T(n) is given by equation 2.
(2)
where Gp and CSp is given by equations 3 and 4 respectively. Gp and CSp refer to general
probability and current state probability.

(3)

where k/N refers to the desired percentage of cluster heads during each round and Ecurrent and Emax is
remaining energy and maximum energy of a node respectively.

(4)

In LDCHS (Handy, M. J., Haase, M., & Timmermann, D. (2002)), authors have modified
threshold T(n) given in Equation 1 to elect cluster head by considering ratio of node’s current energy
with respect to initial energy and it is given by Equation 5.
(5)
LEACH, ALEACH and LDCHS use stochastic approach to select cluster heads with certain
probability. LDCHS and ALEACH improve LEACH protocol by considering current energy of the
nodes to elect cluster heads. However, there is a huge variation into the number of cluster heads
elected and desired number of cluster heads required during each round that results into un-even
energy depletion of the network. Number of cluster heads during each round for LEACH, LDCHS
and ALEACH is presented at the end of the paper.

150


3. PREREQUISITE
3.1 System Model
In this paper, we have considered a sensor network of N nodes that are uniformly distributed
in the region of MxM m2. Following assumptions are made about the sensor nodes and underlying
network (Chen, G., Li, C., Ye, M., & Wu, J. (2009)).
1. Base Station (BS) is located in the center of the node deployment area and it is having infinite
amount of energy.
2. BS and sensor nodes are stationery once they are deployed in the Region of Interest (ROI).
3. All sensor nodes are homogeneous and are assigned unique identifier.
4. All sensor nodes are having limited amount of energy.
5. All sensor nodes are capable of transmitting with different power levels depending upon the
distance from the desired recipient.
6. Communication links are symmetric.
7. Cluster Head always receive highly correlated data from the member nodes. Thus, data
aggregation is possible.
8. Round (r) is known to each and every node.
3.2 Energy Model
We have considered first order of radio model as given in (Heinzelman, W. R.,
Chandrakasan, A., & Balakrishnan, H. (2000, January), Chen, G., Li, C., Ye, M., & Wu, J.
(2009)) for communication energy expenditure. We have used free space model (d2 power loss) and
multipath fading model (d4 power loss) where d is the distance between the transmitting and
receiving nodes. The energy expenditure to transmit l-bit data packet over distance d is given by
equation 6.

(6)

The electronics energy, Eelec, depends on factors such as the digital coding, and modulation,
whereas the ampliﬁer energy, l fsd2 or l fsd4, depends on the transmission distance and the
acceptable bit-error rate (Chen, G., Li, C., Ye, M., & Wu, J. (2009)). To receive this message, the
radio expends energy as given by equation 7. We have also assumed that a cluster head consumes
EDA (nJ/bit/message) amount of energy for data aggregation.
(7)
4. PROPOSED APPROACH
Like LEACH, our proposed approach also works in rounds. Round is the duration for which a
particular node works as a CH. Round consists of two phases. (a) Cluster Head election phase and
(b) Steady State Phase. Both of these phases are described in the following subsections.

151


4.1 Cluster Head Election Phase
A node elects itself as a CH, if its node identifier (id) is within the set of node identifiers that
should be a cluster head during a particular round; otherwise it works as a member node (non-CH
node) for the current round i.e. if total nodes are 100 and desired percentage of cluster heads are set
to 5% of the total nodes then first five nodes are elected as CHs during first round, nodes with the ids
6 to 10 would be elected as the cluster heads during second round; and so on. This process continues
until all nodes become cluster heads. When all the nodes become cluster heads then the process
repeats with nodes with ids 1 to 5 as the CHs. This process ensures that each node becomes a cluster
head exactly once during 1/p rounds where p is the desired percentage of cluster heads. This
proposed approach also ensures that desired percentage of cluster heads should be maintained until
the death of first node. Once nodes are aware that they are elected as CHs during a particular round,
they inform their status to the non-CH nodes within the network. Non-CH node associates with the
one of the CH nodes for which minimum communication energy expenditure is required; and sends a
join message to the selected CH. After getting join messages from the Non-CH nodes, CH nodes
prepares TDMA schedule and inform to the member nodes of their own cluster.
4.2. Steady State Phase
During the steady state phase, all non-CH nodes turn off their radio to save their energy,
except the time slot for which they have to transmit data to CH. CHs perform data aggregation and
send aggregated data to BS after receiving data from the member nodes. This data aggregation
approach helps to save energy of the CH because less number of bits transmitted by CHs. At the end
of Steady State phase a new round begins with CH election phase.
There is a high energy drains for the cluster heads because they have to do CH announcement
to the other nodes, reception of CH Join message, TDMA schedule announcement to the nodes who
have sent CH Join messages, data reception from the member nodes and finally data transmission to
BS after performing data aggregation. Thus, to enhance the network life time, role of the CH is
rotated between all active nodes of the network. Thus, set of nodes xj who are the cluster head for the
round j is different than the set of nodes xj-1 who had been cluster head for the previous round.
5. SIMULATION STRATEGY AND RESULT DISCUSSION
We have simulated our proposed approach – S-LEACH and compared it with the LEACH,
ALEACH and LDCHS protocols for a random network of 50 nodes, 100 nodes and 200 nodes
uniformly deployed in a region of 100m x 100m with initial energy 0.25J/node, 0.5J/node and
0.75J/node. Simulation parameters used for the verification of the proposed approach is given in the
Table 1.
Table 1. Simulation Parameters
Parameter Name
Value
Simulation Area
100m x 100m
Total Nodes
(1)
50 (2) 100 and (3) 200
Cluster Heads (in %)
5
Initial Energy (J/Node)
(1)
0.25 (2) 0.5 (3) 0.75
Transmitter Electronics and Receiver
50 nJ/bit
Electronics
Transmit Amplifier
100 pJ/bit/m2
Energy for Data Aggregation
5nJ/bit/message
Message Size
4000-bit
152


Figure 1. Death of Nodes and number of Cluster Heads for a network of 50 nodes with initial energy
0.25J/Node

Figure 2. Number of Cluster Heads for S-LEACH
algorithm for a network of 50 nodes with initial
energy 0.25J/Node

Figure 3. Number of Cluster Heads for
ALEACH algorithm for a network of 50 nodes
with initial energy 0.25J/Node

Figure 4. Number of Cluster Heads for LEACH
energy 0.25J/Node

Figure 5. Number of Cluster Heads for LDCHS
energy 0.25J/Node
153


0.5J/Node

0.75J/Node

0.25J/Node
154


0.5J/Node

0.75J/Node

0.25J/Node

155


0.5J/Node

0.75J/Node
We have shown death of nodes and number of cluster heads during each round in Figures 113 for a network of 50, 100 and 200 nodes with initial energy 0.25, 0.5 and 0.75 J/node. Simulation
results show that First Node Dies (FND) is poor for the proposed approach compared to LEACH,
LDCHS and ALEACH protocols. However, our proposed approach improves overall network
lifetime. Also, number of cluster heads for S-LEACH, ALEACH, LEACH and LDCHS is shown
separately in Figures 2-5 respectively and their comparative result is shown in Figure 1. S-LEACH
maintains desired percentage of cluster heads during each round until the death of first node and
same can be verified from Figure 2. This is the reason why S-LEACH outperforms to LEACH,
LDCHS and ALEACH protocols
6. CONCLUSION
In this paper, we have proposed S-LEACH protocol, which is distributed in nature, sustain
with the node density and provides improved network lifetime compared to LEACH, LDCHS and
ALEACH protocols. In S-LEACH, we have used sequential selection approach to maintain desired
percentage of cluster heads during each round until the death of first node. Our protocol enhances
overall network lifetime compared to LEACH, LDCHS and ALEACH but First Node Dies (FND) is
not as good as LEACH, LDCHS and ALEACH.
156


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