incorporating fault tolerance in leach protocol

Incorporating Fault Tolerance in LEACH Protocol for Wireless Sensor

Networks

Rudranath Mitra

1, Anurupa Biswas

2

Department of Information Technology

Heritage Institute of Technology

Anandapur,Kolkata-700107.INDIA.

[email protected]

Abstract

Routing protocols have been a challenging

issue in wireless sensor networks. WSN is one of

the focussed are of research because of its multi-

aspect applications. These networks are self-

organized using clustering algorithms to conserve

energy. LEACH (Low-Energy Adaptive Clustering

Hierarchy) protocol[1] is one of the significant

protocols for routing in WSN. In LEACH, sensor

nodes are organized in several small clusters

where there are cluster heads in each cluster. These CHs gather data from their local clusters

aggregate them & send them to the base station.

On the LEACH many new schemes have been

proposed to enhance its activity like its efficiency,

security etc. In this paper the fault tolerance issue

is being incorporated.

Key words: Cluster-head, CH, BS, LEACH, fault

tolerance.

1. Introduction

A clustered architecture organizes the sensor nodes

into clusters, where each cluster is governed by a

cluster-head. The nodes in each cluster are involved

in message exchanges with their respective cluster-

heads & these CHs send messages to their

respective BSs, which is usually an access point

connected to a wired network.

Fig. 1 represents a clustered architecture where

any message can reach the BS by at most 2 hops.

Clustering can be extended to greater depths

hierarchically. Clustered architecture is specially

useful for sensor networks because of its capability

for data fusion. The data gathered together by all

members of the cluster at the cluster-head and only

the resulting information are sent to the BS. Hence

sensor networks should be self-organizing as well

as the cluster information & election of cluster-

heads must be an autonomous, distributed process.

This is achieved through LEACH.

Fig.1

Fig. 1 represents a clustered architecture where any

message can reach the BS by at most 2 hops.

Clustering can be extended to greater depths

hierarchically. Clustered architecture is specially

useful for sensor networks because of its capability

for data fusion. The data gathered together by all

members of the cluster at the cluster-head and only

the resulting information are sent to the BS. Hence

sensor networks should be self-organizing as well

as the cluster information & election of cluster-

heads must be an autonomous, distributed process.

This is achieved through LEACH.

LEACH is a clustering-based protocol that

minimizes energy dissipation in sensor networks.

LEACH randomly selects nodes as cluster-heads &

periodic reelection for CHs is performed. It helps in

energy dissipation among nodes in the network

instead of depending on only one node (cluster-

Rudranath Mitra et al, International Journal of Computer Science & Communication Networks,Vol 2(3), 380-384

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ISSN:2249-5789

mailto:[email protected]

head). Each iteration of selection of CHs is called a

round.

The operation of LEACH is split into two

phases: Set up & Steady.

During the set up phase, each sensor node

chooses a random number between 0 & 1. If it is

lower than the threshold for node n, T(n), the

sensor node becomes a cluster-head.

The threshold T(n) is calculated as [2]:

Where P is the desired percentage of

nodes which are CHs, r is the current

round, and G is the set of nodes that has

not been CHs in the past 1/P rounds. It

ensures that all nodes eventually spend

equal energy. After selection the CHs

advertise their selection to all other nodes.

All nodes chooses their nearest CH after

receiving advertisements based on the

received signal strength. The CHs then

assign a TDMA schedule for their cluster

members. This allows the sensor nodes of

the cluster to turn off their transceiver

except at the time slot allocated to them.

Therefore it is saving considerable energy.

During the steady phase, data transmission takes

place based on TDMA schedule and the CHs

perform data aggregation/ fusion through local

computation. The BS receives only aggregated data

from cluster-heads, leading to energy conservation.

After a certain period of time in the steady phase

CHs are again selected through the set-up phase.

LEACH has been come out to be primary

clustering protocol in the WSNs as well it has

shown energy efficiency & effectiveness [3][4][5].

Hence LEACH has been chosen as the plot for

implementation of fault tolerance.

2. Related Works

The idea proposed in LEACH has been an

inspiration for many hierarchical routing protocols,

although some protocols have been independently

developed. Since sensor nodes are often placed in

harsh zone [6], sensor nodes area prone to failure.

Supposed if a cluster-head is faulty it can leave a

cluster disconnected from the base station until the

network reorganizes again.

So we see fault tolerance problem is a

very big problem in WSN. Several works has been

done on fault tolerance over many clustering

algorithms. One fault tolerance approach has been

discussed in [7]. Here also the research work is

done on LEACH. Here fault recovery is suggested

in two ways: inter-cluster recovery & intra

cluster recovery.

Another research work on fault tolerance

is discussed in [8]. Here a Dynamical Jumping

Real-time Fault-tolerant Routing Protocol (DMRF)

has been proposed. Once node failure, network

congestion or void region occurs then the

transmission mode will switch to jumping

transmission mode leading to reduced transmission

delay and guarantees the data packet to be sent to

its desired destination within the specified time

limit. Each node can dynamically adjust the

jumping probabilities to increase the ratio of

successful data transmission by using feedback

mechanism. This mechanism results in reduced

effect of failure nodes, congestion and void region

and reduced transmission delay, reduced number of

control packets and higher ratio of successful

transmission.

One more fault tolerant work is discussed

in [9]. Basically, WSNs faces resource limitations,

high failure rates and fault caused by wireless

channels & wireless sensor nodes. It increases the

reliability & robustness of the network by creating

a backup path for every node on a main path of

data delivery. When a node gets failure it

immediately applies its backup path as the main

path for data delivery of next incoming packets.

This protocol reduces the number of dropped data packets and increases robustness of the entire

network by maintaining the continuity of data

packet transmission even in presence of faults.

3. Proposed Scheme

In this scheme, fault is detected in a general way

that if no response comes from the CH to BS or the

subordinates then it is considered that the cluster-


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head is faulty and is become unable to transfer

data.According to this scheme, there may be

tworecovery mechanisms:Replace the faulty

cluster-head by the next highest energy node in the

cluster.

Maintain two cluster-heads in each cluster by using

token.

3.1. Illustration

To avoid redundancy effect one token will be

passing in between the two cluster-heads. When

CH1 is active then the token will be kept by that

CH (means CH1) and CH2 will not hold any token

then. CH2 will have all the replica information

from the communicating nodes. Until CH1 gets

faulty, CH1 is responsible for gathering all the

information from the subordinates to fuse the data

& send to BS. So, until CH1 gets faulty i.e., CH1 is

working properly, CH2 gets all the data from the

nodes those are sending data to CH1 but CH2 is

receiving data only, not sending any reply to those

nodes.

To make all the nodes know that the CH2 is alive

i.e., not faulty, CH2 will periodically send a ping

message to all the nodes.

When CH1 gets faulty, then CH2 becomes

responsible for the same activities that CH1 was

doing. That means till then CH2 will be gathering

all the information from the subordinates to fuse

the data and send them to the BS.

In case if CH2 becomes faulty while CH1 was

working properly, then next highest energy node

will be selected as CH2 & will act as that

mentioned earlier.

When CH1 has already become faulty and CH2 is

playing the role of CH1, then also the next highest

energy node will be selected as CH2. The entire

procedure is pictorially well described in fig.2.

When both CH1 & CH2 will stop working

simultaneously by chance, then according to fig.2

the entire process has to be begun, that means from

the advertising phase.

If some of the subordinate nodes are

faulty, then we can implement redundancy of

subordinates. The expense to maintain this much of

redundant nodes will be greater than the

expenditure of maintaining two cluster-heads.

4. Fault Detection Algorithm

1. Initialize CH1 & CH2 & subordinates

2. IF no response comes within a TDMA slot

THEN

3. Set CH1 as Faulty

4. ELSE

5. For CH2

6. IF no ping message comes periodically

THEN

7. Set CH2 as Faulty


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5. Results

6. Comparative Study

LEACH Fault

Tolerant

LEACH

Network lifetime

Very Good

Near to LEACH

Fault Detection

Capability

No Yes

Fault Recovery

Capability

No Yes

7. Advantages

1. It is capable of avoiding incorporating

redundancy of sensor nodes and paths into

clusters in WSN.

2. By avoiding redundancy, it is capable of

incurring expenditure of maintenance of

the redundant nodes and paths.

3. Since LEACH is already a significant

protocol in WSN due to its several

applications, incorporating fault tolerance

in LEACH makes LEACH more

significantly tempting protocol in WSN

research issue.

8. Conclusion

Several new schemes for fault tolerance

have been proposed on clustering algorithms in

WSN because fault tolerance is one of the most

challenging issues in WSN. In some papers the

jumping transmission mode is explored to

guarantee real-time and fault tolerant

characteristics. Some feedback mechanisms are

used to enhance successful transmission ratio.

LEACH is one of the most important &

significant protocols for research issues in WSN.

Through simulation it is shown that significant

improvement is achieved in coverage and fault

tolerance with a minimal trade-off in terms of

reduced network lifetime.

8. Acknowledgements

We express our sincere gratitude to the Head of the

Dept. and the members of the Research Team,

Dept.-of-Information Technology,Heritage Institute

of Technology.We do also acknowledge Smt. Baby

Mitra,Sudeshna Chatterjee,Doel Mitra and Peali

Juva for constant support and encouragement.

9. References

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[3] Guowei Wu 1, Chi Lin 1, Feng Xia 1,*, Lin Yao

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incorporating fault tolerance in leach protocol

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