Leach

LEACH

Cluster-based Routing Protocol

for

Wireless Sensor Networks

By

AKANKSHA UPADHYAY

Research Student, SATI, Vidisha

Need

• Cheap and energy-efficient as possible and rely on their large

numbers to obtain high quality results.

• Fault tolerance while minimizing energy consumption.

• Since the limited wireless channel bandwidth must be shared

among all the sensors in the network, routing protocols for

these networks should be able to perform local collaboration to

reduce bandwidth requirements.

AKANKSHA UPADHYAY, Research Student, SATI, Vidisha

Network routing protocols for WSNs

(Energy Analysis)

• Direct communication with BS

• Minimum energy multi-hop routing using sensor networks and

radio models

• Clustering


Direct communication with BS

• Each sensor sends its data directly to the base station.

• Possibly optimal if either the base station is close to the nodes,

or the energy required to receive data is large.


Minimum energy multi-hop routing

• Nodes route data destined ultimately for the base station

through intermediate nodes.

• The intermediate nodes are chosen such that the transmit

amplifier energy is minimized.

• Rather than just one (high-energy) transmit of the data, each

data message must go through n (low-energy) transmits and n

receives

• Shorten system lifetime as the nodes closest to the base station

are the ones to die out first since they are the ones most used

as “routers” for other sensors’ data.


Clustering

• Nodes are organized into clusters that communicate with a

local base station, and these local base stations transmit the

data to the global base station, where it is accessed by the end-

user.

• If the base station is an energy-constrained node, it would die

quickly, as it is being heavily utilized.


LEACH

• Low-Energy Adaptive Clustering Hierarchy

• Clustering-based protocol

• Select sensor nodes as CHs by rotation, so the high energy

dissipation in communicating with the BS is distributed evenly

to all sensor nodes in the network.


Assumption

• The base station is fixed and located far from the sensors.

• All nodes in the network are homogeneous and energy

constrained.


Key Features

• Localized coordination and control for cluster set-up and

operation.

• Randomized rotation of the cluster “base stations” or “cluster-

heads” and the corresponding clusters.

• Local compression to reduce global communication.


LEACH

• The nodes organize themselves into local clusters, with one

node acting as the local base station or cluster-head.

• Cluster-head nodes broadcast their status to the other sensors

in the network.

• Each sensor node determines to which cluster it wants to

belong by choosing the cluster-head.

• Each cluster-head creates a schedule for the nodes in its

cluster.

• Once the cluster-head has all the data from the nodes in its

cluster, the cluster-head node aggregates the data and then

transmits the compressed data to the base station.


Comparative Analysis

System lifetime using direct transmission,

MTE routing, static clustering, and

LEACH with 0.5 J/node

Total system energy dissipated using

direct communication, MTE routing

and LEACH for the 100node random

network,

Eelec=50nJ/bit, εamp=100pJ/bit/m2 and

the messages are 2000 bits AKANKSHA UPADHYAY, Research Student, SATI, Vidisha

Algorithm

• The operation of LEACH is broken up into rounds.

• Each round comprises 2 phases

1. Set-up phase: when the clusters are organized,

2. Steady-state phase: when data transfers to the base

station.


Set-up Phase

• Decision of nodes to become cluster head

• Node n selects random number between 0 and 1

• If number is less than threshold T(n), node become cluster head for current round. [T(n)]

• Cluster head nodes uses CSMA MAC protocol to broadcast advertisement message to the rest of the nodes with same transmit energy.

• According to the received signal strength nodes decides the cluster to which it will belong in the round.

• Each node transmit information of its cluster head selection to the cluster head again using CSMA MAC protocol.

• Cluster head creates a TDMA schedule telling the nodes when to transmit.


Set-up Phase

Threshold Computation

[BACK]

)1

mod(*1P

rP

P

T(n) =

if n ϵ G

0 otherwise

n = node

P = the desired percentage of cluster

heads

r = the current round

G = set of nodes that have not been

cluster-heads in the last 1/P

rounds

During round 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.

After 1/P-1 rounds, T=1for any

nodes that have not yet been

cluster-heads.

And after 1/P rounds, all nodes

are once again eligible to become

cluster-heads.


Steady-state Phase

• The radio of each non-cluster-head node can be turned off

until the node’s allocated transmission time ( according to

TDMA schedule).

• The cluster-head node must keep its receiver on to receive all

the data from the nodes in the cluster.

• When all the data has been received, then cluster head node

performs signal processing functions to compress the data into

a single signal.

• This composite signal is sent to the base station.


Conclusion

• LEACH distributes the energy among the nodes in the network

and is effective in reducing energy dissipation from a global

perspective.

• LEACH effectively enhances the system lifetime.

• LEACH is completely distributed, requiring no control

information from the base station, and the nodes do not require

knowledge of the global network in order for LEACH to

operate.


Reference

W.R. Heinzelman, A. Chandrakasan, H. Balakrishnan, “Energy-Efficient

Communication Protocol for Wireless Microsensor Networks”, Proceedings of the 33rd Annual Hawaii International Conference on System Sciences, Maui, HI, USA, pp. 10–19, 4–7 January 2000.


THANK YOU

Leach

Technology

clusterhead nodes

sensor nodes

cluster base stations

clustering nodes

intermediate nodes

global base station

cluster heads

cluster setup