Protocol Enhancements in LEACH

International Journal of Science and Engineering Applications
Volume 4 Issue 4, 2015, ISSN-2319-7560 (Online)
www.ijsea.com 218
Protocol Enhancements in LEACH
Neha Aggarwal
Electronics & Communication, IIMT Meerut
Meerut, India
Abstract-LEACH is a hierarchical protocol in which most nodes transmit to cluster heads, and the cluster heads aggregate and
compress the data and forward it to the base station (sink).In LEACH, a TDMA-based MAC protocol is integrated with clustering and
a simple “routing” protocol. The goal of LEACH is to lower the energy consumption required to create and maintain clusters or to use
the energy of the nodes in such a manner so as to improve the life time of a wireless sensor network. In this paper we are presenting an
overview of the different protocol changes made in LEACH to improve network lifetime, throughput, coverage area of network etc.
Keywords-LEACH, E-LEACH, Enhanced LEACH, EHE-LEACH, Multi-level Leach
1. LEACH: PROTOCOL EXPANATION
LEACH, Low-energy Adaptive Clustering Hierarchy,
presented by Wendi B. Heinzelman of MIT, is application
specific protocol architecture for Wireless Sensor Network
(WSN). It assumes a dense sensor network of homogeneous,
energy-constrained nodes, which shall report their data to a
sink node. It has become one of the most used bases for
developing new architecture protocols or modifying the
existing one in WSN.
LEACH [6] is a TDMA-based MAC protocol which is
integrated with clustering and a simple routing protocol in
wireless sensor network. LEACH partitions the nodes into
clusters and in each cluster a dedicated node, the
clusterhead, is responsible for creating and maintaining a
TDMA schedule; all the other nodes of a cluster are member
nodes. To all member nodes, TDMA slots are assigned, which
can be used to exchange data between the member and the
clusterhead; there is no peer-to-peer communication. Except
their time slots, the members can spend their time in sleep
state. The clusterhead aggregates the data and transmits it to
the sink. Since the sink is often far away, the clusterhead must
spend significant energy for this transmission. For a member,
it is typically much cheaper to reach the clusterhead than to
transmit directly to the sink. The clusterheads role is energy
consuming since it is always switched on and is responsible
for the long-range transmissions. If a fixed node has this role,
it would burn its energy quickly, and after it died, all its
members would be “headless” and therefore useless.
Therefore, this burden is rotated among the nodes.
Specifically, each node decides independent of other nodes
whether it becomes a clusterhead, and therefore there is no
signalling traffic related to clusterhead election (although
signalling traffic is needed for subsequent association of
nodes to some clusterhead). This decision takes into account
when the node served as clusterhead the last time, such that a
node that has not been a clusterhead for a long time is more
likely to elect itself than a node serving just recently. The
protocol is round based, that is, all nodes make their decisions
whether to become a clusterhead at the same time and the
nonclusterhead nodes have to associate to a clusterhead
subsequently. The nonclusterheads choose their clusterhead
based on received signal strengths. The network partitioning
into clusters is time
variable and the protocol assume global time synchronization.
After the clusters have been formed, each clusterhead picks a
random CDMA code for its cluster, which it broadcasts and
which its member nodes have to use subsequently. This
avoids a situation where a border node belonging to
clusterhead A distorts transmissions directed to clusterhead B,
shown in Figure1.
Fig 1
A critical network parameter is the percentage of nodes that
are clusterheads. If there are only a few clusterheads, the
expected distance between a member node and its clusterhead
becomes longer and therefore the member has to spend more
energy to reach its clusterhead while maintaining a given BER
target. On the other hand, if there are many clusterheads, there
will be more energy expensive transmissions from
clusterheads to the sink and less aggregation. Therefore, there
exists an optimum percentage of clusterheads, which for the
scenario investigated in is ≈5%. If this optimum is chosen,
LEACH can achieve a seven to eight times lower overall
energy dissipation compared to the case where each node
transmits its data directly to the sink, and between four and
eight times lower energy than in a scenario where packets are
relayed in a multi-hop fashion. In addition, since LEACH
distributes the clusterhead role fairly to all nodes, they tend to
die at about the same time.
The protocol is organized in rounds and each round is
subdivided into a setup phase and a steady-state phase,
Figure2. The setup phase starts with the self-election of
nodes to clusterheads.

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In the following advertisement phase, the clusterheads
inform their neighborhood with an advertisement packet. The
clusterheads contend for the medium using a CSMA protocol
with no further provision against the hidden-terminal problem.
Fig 2
The nonclusterhead nodes pick the advertisement packet with
the strongest received signal strength. In the following cluster-
setup phase, the members inform their clusterhead (“join”),
again using a CSMA protocol. After the cluster setup-phase,
the clusterhead knows the number of members and their
identifiers. It constructs a TDMA schedule, picks a CDMA
code randomly, and broadcasts this information in the
broadcast schedule sub phase. After this, the TDMA steady-
state phase begins. Because of collisions of advertisement or
join packets, the protocol cannot guarantee that each
nonclusterhead node belongs to a cluster. However, it can
guarantee that nodes belong to at most one cluster as shown in
Fig 3.
Fig 3
The clusterhead is switched on during the whole round and
the member nodes have to be switched on during the setup
phase and occasionally in the steady-state phase, according to
their position in the cluster’s TDMA schedule.
Nodes that have been cluster heads cannot become cluster
heads again for P rounds, where P is the desired percentage of
cluster heads. Thereafter, each node has a 1/P probability of
becoming a cluster head in each round.
In the setup phase, each node decides whether or not to
become a cluster head for current round. The selection
depends on decision made by the node by choosing a random
number between 0 and 1. If the number is less than the
threshold T(n), the node becomes a clusterhead for the current
round. The threshold is set as:
, if n € G;
T(n) =
0 , else
Where p is the probability of the node being selected as a
cluster-head node, r is the number of rounds passed, and G is
the set of nodes that have not been cluster-heads in the last 1/p
rounds, mod denotes modulo operator. Nodes that are cluster
heads in round r shall not be selected in the next 1/p rounds.
The random selection algorithm for LEACH easily leads to
the imbalance of the stored energy of sensor nodes, thereby;
the consumption of system energy is increased.
2. Enhanced LEACH
In LEACH protocol, time is divided into many rounds, in each
round, all the nodes contend to be cluster head according to a
predefined criterion. Enhanced LEACH [1] protocol was
proposed to set the time length of each round, to prolong the
lifetime of the network and increase throughput, which is
denoted as the amount of data packs sent to the sink node.
LEACH protocol lets the data transmission phase last for a
fixed period of time, then enter into a new round of cluster
head election. The time length of round has obviously
influence on the performance of LEACH protocol. In order to
decrease the overhead of set-up phase, we hope to increase the
time length of round, which increases the time for data
transmission. However, prolonging the time length of round
also increases the energy consumption of cluster head, which
will causes some nodes die early and in turn shortens the
lifetime of wireless sensor networks. So, regarding to
configuration of time length of round, there is a trade-off
between lifetime and throughput.
If the time of set-up phase is α, and the steady data
transmission time is t , then the time length of every round is tr
= α + t . Let the time when the first sensor node dies as the
lifetime of the network, which is denoted as tfnd .
tfnd = n (α + t ), Where n is the number of rounds after which
the first sensor node dies.
Fig 4
According to LEACH protocol, there are m frames in the time
t, so frame t = m⋅T, here frame T is the time length of each
frame. As the time length of a round increase with m,
increasing m will increase the energy consumption of cluster
head in a round, which makes the energy consumption in the
network unbalanced. Therefore, some nodes will die early and

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in turn shortens the lifetime of wireless sensor networks. So as
per Fig 5 and Fig 6, m=5 is good for trade-off between
lifetime and throughput.
Fig 5
Fig 6
3. E-LEACH
In the E-LEACH [2] algorithm, the original way of the
selection of the cluster heads is random and the round time for
the selection is fixed. The nodes with low remnant energy
have the same priority to be a cluster head as the node with
high remnant energy. Therefore, those nodes with less
remaining energy may be chosen as the cluster heads which
will result that these nodes may die first. In the E-LEACH
algorithm, we consider the residual power of the sensor nodes
in order to balance network loads and changes the round time
depending on the optimal cluster size.
The cluster heads communicate with the base station in
single-hop mode which makes LEACH inefficient to be used
in large-scale wireless sensor networks for the limit effective
communication range of the sensor nodes. The E-LEACH
adopts the same round concept with the original LEACH. In
hierarchical routing protocols, the number of cluster-heads is
a key factor that affects the performance of routing protocols.
If the number of cluster-heads is less, each cluster-head needs
to cover larger region, this will lead the problem that some
cluster-members get far from their cluster-heads and consume
much more energy. As the communication between cluster
heads and the base station needs much more energy than
common nodes, the excessive number of cluster-heads will
increase the energy consumption of the whole network and
shorten the network lifetime. Therefore, it is necessary to
select optimal clusterhead number to make the energy
consumption minimum. In the E-LEACH we use the
minimum spanning tree between clusterheads, choose the
cluster head which has largest residual energy as the root
node. Fig 7 depicts the architecture of ELEACH.
Fig 7
Fig.8 is the comparison of FND and HND between LEACH
and E-LEACH. If the system lifetime is defined as the number
of rounds for which the first node dies, E-LEACH algorithm
can reach 1529 rounds, whereas LEACH only reaches 1029
rounds. The system lifetime is improved by 49% of E-
LEACH algorithm than LEACH.
Fig 8
The simulation results show that our proposed protocol
increases network lifetime at least by 40% when compared
with the LEACH algorithm.
4. EHE-LEACH
The major problem of the sensor node is the limited energy.
Therefore, energy efficiency in the design of routing protocols
for sensor networks is of principal requirement. EHE-LEACH
[3] (Enhanced HEterogeneous - Low Energy Adaptive Cluster
based Hierarchical protocol) is based on the fixed distance
threshold, which is used to bifurcate the coverage area, used
two separate mechanism direct diffusion and clustering. From
a survey it is observed that minimum two hop data
transmission is required for the cluster based communication,
from source to BS even though the distance between source

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and BS is very small. This consumes extra execution time for
the completion of a round.
From Fig. 9 it is clear that d3 > d2 > d1. For LEACH protocol
single hop communication is not, minimum two hope
communication is required.
Fig 9
In the proposed model two parameters are considered: firstly-
minimize the execution time of a round to some extent by
using direct diffusion. Secondly- maximizes the lifetime and
stability of the network by using the combination of two
techniques simultaneously direct diffusion and clustering. The
half nodes alive (HNA) & last node alive (LNA) are the key
parameters used for the measurement of lifetime and the
stability of the system. SNs near to the BS communicate
directly and those which are far away from the BS use cluster
based communication. To evaluate the performance of the
proposed scheme two key parameters known as: Half Nodes
Alive (HNA) and Last Node Alive (LNA) are selected. By
selecting the distance based threshold with the ratio of 1:9
between direct communication and cluster based
communication it has been observed that EHE-LEACH has
better network lifetime with respect to various parameters in
comparison to the other well-known proposals such as
LEACH.
5. Multi-Level LEACH
Although LEACH protocol conserves energy in the nodes and
prolongs the lifetime of the WSN application, it still has the
following problems:
• Randomized rotation of the CH without considering the
residual energy in the nodes.
• As the network size increases the CH's which are far away
from the BS drain their energy sooner.
If the deployment area is less, the LEACH protocol works
well. Since the LEACH protocol cannot be used over large
areas, a Hierarchical routing protocol based on the LEACH.
In Hierarchical routing protocol [4] the CHs are divided into
various levels so that each
CH at a level i transmits the data to its higher level, (i + 1)
level CH, instead of transmitting the data to the BS directly.
Two-level LEACH (TL-LEACH), Three-level LEACH (3L-
LEACH), Four-level LEACH (4L-LEACH) can be
implemented to install multi-level LEACH.
5.1 TL-LEACH
In this, we have a two- level structure consisting of leaf nodes,
level-l CH's, level-2 CH's. One of the level-l CH's is chosen as
level-2 CH as shown in figure 3. After collecting the data, a
level-l CH forwards the same to its level-2 CH. This level-2
CH aggregates the data received from its level-l CH's and the
same aggregated data is forwarded to the BS resulting in
energy savings. The operation TL-LEACH can be divided
into the following 3 phases, namely:
 Selection of level-l and level-2 CH's
 Set up phase
 Steady state phase
1) Selection of level-l and level-2 CH's:
In this the level- 1 CH is elected as given in the LEACH
protocol. After the election of level-l CHs, the level-2 CH
election is initiated. Among level- 1 CHs, the CH with
maximum residual energy and proximate to the BS is elected
as the level-2 CH as shown figure 3. In addition to its current
role as level-l CH, the node acts as level-2 CH as well.
2) Set-up Phase:
After the election of level-l CHs, each CH broadcasts an
advertisement message to all its leaf nodes. Each leaf node
based on received signal strength from all the CHs, decides
which CH to join. Then each leaf node transmits an
acknowledgement message to its chosen CH along with its
node ID. Each level-l CH records the node IDs of its member
nodes. The set up phase for level-2 CH is also similar. In this
case, level-l CHs are treated as the leaf nodes. Each level-l
CHs sends a message containing the number of its member
and its own node ID to the elected level-2 CH. Thus, a level-2
CH has information regarding its level-l CHs and their
associated leaf nodes. So based on this information a level-2
CH creates a TDMA schedule to its members and broadcasts a
message.
3) Steady state phase:
In the steady state phase transmission of the data takes place.
Each leaf node sends the sensed data to its respective CH
within its allocated time slot. Until their allocated time slot the
leaf nodes can turn off their radio so that energy can be saved.
All the leaf nodes transmit their data to its respective level-l
CH. And the level-l CHs aggregate all the sensed data. The
aggregated data received by the level-l CH is forwarded to
their level-2 CH based on its allocated time slot. Thus the data
collected by the level-2 CH is sent to the BS. Thus the data
from a leaf node to the BS is transmitted using level-l CH and
then level-2 CH. Considerable energy in the WSN application
can be saved with this type of hierarchical routing.
Fig 10
This work presents a multi-level hierarchical routing protocol,
which is based on the LEACH protocol. This protocol
improves both the energy efficiency and the lifetime of the
network. Two-level LEACH (TL-LEACH), Three-level

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LEACH (3L-LEACH) and Four-level LEACH (4L-LEACH)
have been presented. Analysis (done using NS3) shows that
the hierarchical routing protocols, TL-LEACH, 3L-LEACH
and 4L-LEACH, are better than the LEACH protocol.
It can be concluded that the multi-level Hierarchical routing
protocol is more energy efficient when compared to the
LEACH. The lifetime of the network also gets extended. As
the deployment area of WSN increases, the 3L-LEACH and
4L-LEACH perform well when compared to the 2L-LEACH.
6. Op-LEACH
LEACH uses a TDMA based MAC protocol, in order to
maintain balanced energy consumption. The TDMA schedule
maintained by Cluster Head evenly distributes the slots to all
of the sensor nodes in its cluster. A number of these TDMA
slots are wasted when the nodes have random data
distribution. A modification to existing LEACH protocol is
needed in order to use the slots corresponding to nodes that do
not have data to send at its scheduled slot.
Op-LEACH [5] improves the performance of LEACH
algorithm in terms of energy and time delay in real time
networks. Every sensor node does not have data all the time.
The data is available in random fashion. The sensors may be
event driven, so data may be available only when they sense
the event. The proposed method is utilizing the slots
belonging to the node having no data to send. This method
turns free slots into useful slots without making any changes
in the TDMA schedule. This will reduce the waiting time for
sensor nodes because now sensor nodes can get more than one
slot per frame. It will reduce the data transmission delay and
increase throughput of the network. The real time sensors are
mostly event driven. So until the event occurs, the nodes will
not have the data to process or to send (to the cluster head). So
the corresponding slots become idle. The proposed algorithm
utilizes these idle slots for some other node’s data
transmission. At the end of setup phase every non cluster head
member knows about transmission schedule. Every node
waits for its turn to transmit data and if a node does not have
any data to transmit, the slot is allotted to the next sensor in
TDMA schedule. This algorithm makes the free slots
available to sensor nodes with higher traffic without
additional overhead Op-LEACH shows effective performance
difference when the data sensed by network nodes is uneven.
7. CONCLUTION
With the protocols discussed so far, it is clear that LEACH
would not be able to cover large geographical areas of some
square miles or more, because a clusterhead two miles away
from the sink likely does not have enough energy to reach the
sink at all. If clusterheads use other clusterheads for
forwarding, this limitation can be mitigated. Even the slots are
wasted in uneven traffic conditions which can be allotted to
other nodes for forwarding. Energy efficiency is a key design
issue in WSN and must be enhanced in order to improve
network life time. Many such modifications can be made in
LEACH to increase lifetime and throughput.
8. REFERENCES
[1] “Enhancing the Performance of LEACH Protocol in
Wireless Sensor Network” IEEE INFOCOM 2011
Workshop on M2MCN-2011.
[2] “Improvement of LEACH protocol for WSN” 2012 9th
International Conference on Fuzzy Systems and
Knowledge Discovery (FSKD 2012).
[3] “EHE-LEACH: Enhanced heterogeneous LEACH
protocol for lifetime enhancement of wireless SNs”,
2013 International Conference on Advances in
Computing, Communications and Informatics (ICACCI).
[4] Multi-level LEACH Protocol model using NS-3, 2014
IEEE International Advance Computing Conference
(IACC).
[5] Op-LEACH: An Optimized LEACH Method for busty
traffic in WSNs, 2014 Fourth International Conference
on Advanced Computing & Communication
Technologies.
[6] Holger Karl and Andreas Willig “PROTOCOLS AND
ARCHITECTURES FOR WIRELESS SENSOR
NETWORKS”, John Wiley & Sons.

Protocol Enhancements in LEACH

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