wireless sensor network protocols dr. monir hossen ece, kuet department of electronics and...
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Wireless Sensor Network Protocols
Dr. Monir HossenECE, KUET
Department of Electronics and Communication Engineering, KUET
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Clustering Algorithm Clustering of the Large Sensor Network Classification of Clustering Algorithms Popular Clustering Algorithms MAC Protocol Different MAC protocols
Agendas of This Lecture
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Clustering Algorithm (1/2)
Clustering is the way where the sensor nodes are grouped in order to => Achieve the network scalability => Solve the network coverage and traffic unbalance problems among the cluster heads (CHs) => Reduce the size of the routing table stored at the individual node => Distribution of nodes among the clusters evenly => Save the energy consumption by reducing data repetition
Improve network lifetime Reduce network traffic and the contention for the channel Data aggregation and updates take place in CHs
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• Nodes divided in virtual group according to some rules• Nodes belonging in a group can execute different functions
from other nodes
Cluster member
Clusterhead
Gateway node
Intra-Cluster link
Cross-cluster link
Clustering Algorithm (2/2)
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Clustering of the Large Sensor Network (1/2)
An efficient clustering algorithm is important for following reasons:
=> To limit the maximum hop distance => To distribute the nodes among the clusters evenly=> To management of time frame properly => To solve the traffic unbalance problem among CHs => To optimize the no. of CH & hop to ensure the network coverage
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Clustering of the Large Sensor Network (2/2)
1 2 3 4 5 6 7 80.0
0.2
0.4
0.6
0.8
1.0
Cov
erag
e ra
tio
Maximum number of hops in a cluster
CH=2 CH=4 CH=6 CH=8
The curves represent the coverage ratio of
total 500 nodes randomly distributed in 500x500 m2 area,
where maximum distance of a hop is
40 m.
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Classification of Clustering Algorithms (1/2)
Yes
Grant registration
Report to OLT
Receive registration
request from node
No Hop distance
≤ Hlim
OLT selects ONU to register
Node registration algorithm
Here, Hlim is the maximum no. of hops for a cluster
Major Approaches for clustering of WSN:
1. Independent clustering algorithm2. Cooperative clustering algorithm
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Independent Clustering Algorithm (1/2)
Independent clustering Algorithm:
Assignment of large Hmax causes nonsymmetrical node distribution among the clusters
Assignment of small Hmax reduces coverage, all the nodes are not connected
Optimum number of hop selection is required Estimation of the Optimum hop number in
advance is difficult
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Independent Clustering Algorithm (2/2)
Nodes under ONU1=175Nodes under ONU2=125Nodes under ONU3=121Nodes under ONU4=79Maximum hop distance=7
Independent clustering for 500 nodes in an area of 500×500 square meter.
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Cooperative Clustering Algorithm (1/2)
Cooperative clustering algorithm:
Can obtain even distribution of sensor nodes among the clusters
Provides less number of hops in a cluster
Total aggregated traffic in the network is less than the independent clustering algorithm
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Cooperative Clustering Algorithm (2/2)
Nodes under CH1=120, CH2=127, CH3=120, CH4=120 and non-registered nodes=13 up to 4-hops
CH1= 121 CH2= 132 CH3= 123 CH4= 124Up to 5-hops
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Popular Clustering Algorithms
Different clustering algorithms have been proposed to achieve energy and delay efficient WSN
Low Energy Adaptive Clustering Hierarchy (LEACH)
Hybrid Energy Efficient Distributed (HEED) Protocol
Weighted Clustering Algorithm (WCA)
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Low Energy Adaptive Clustering Hierarchy (LEACH)
Every node elects as CH the node that requires the least energy consumption for communication.Every CH set-up a TDMA schedule and transmitted to the nodes. Every node could transmit data in the corresponding time-slot.
Weakness of LEACH Limited scalability Could be complementary to clustering techniques
based on the construction of a DS
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Hybrid Energy Efficient Distributed (HEED) Protocol (1/3)
Assumptions: Sensor quasi-stationary
Links are symmetric
Energy consumption non-uniform for all nodes
Nodes-location unaware
Processing and communication capability-similar
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Hybrid Energy Efficient Distributed (HEED) Protocol (2/3)
Algorithm:• Cluster head selection
Amount of residual energy (primary) and communication cost (secondary) such as node proximity
• Number of rounds of iterations
• Tentative CHs formed
• Final CH until CHprob=1
• Same or different power levels used for intra cluster communication
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Pros:• Balanced clusters• Low message overhead• Uniform & non-uniform node distribution• Inter cluster communication explained• Out performs generic clustering protocols on
various factors
Cons:• Repeated iterations and complex algorithm• Decrease of residual energy smaller
probability number of iterations increased
• Nodes with high residual energy are increased in one region of a network
Hybrid Energy Efficient Distributed (HEED) Protocol (3/3)
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Weighted Clustering Algorithm (WCA) (1/4)
A cluster head can ideally supports nodes to
Ensures efficient MAC functioning
Minimizes delay and maximizes throughput
A cluster head uses more battery power
because it:
Does extra work due to packet forwarding
Communicates with more number of nodes
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Weighted Clustering Algorithm (WCA) (2/4)
A cluster head should be less mobile Helps to maintain same configuration Avoids frequent WCA invocation
A better power usage with physically closer
nodes More power for distant nodes due to signal
attenuation
Weighted Clustering Algorithm (WCA) (3/4)
It is desirable to balance the loads among the clusters
Load balancing factor (LBF) has defined as
i i
cLBF
xn
2
where,
nc is the number of cluster heads xi is the number of nodes of cluster i and
nc
ncN is the average number of neighbors of a
cluster head
Load Balancing Factor (LBF)
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Weighted Clustering Algorithm (WCA) (4/4)
For clusters to communicate with each other, it is
assumed that cluster heads are capable of operating
in dual power mode
A cluster head uses low power mode to communicate
with its immediate neighbors within its transmission
range and high power mode is used for
communication with neighboring clusters
Connectivity is defined as (for multiple component
graph)
Connectivity
N
componentlargestofsizetyconnectivi
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MAC Protocol MAC protocols play a vital role for efficient data
transmission and collision avoidance in a wireless communication system
Different MAC protocols have been proposed to reduce latency as well as energy consumption in WSN
S-MAC, Adaptive S-MAC, LE-MAC, T-MAC, E2-MAC, Sync-LS (Synchronised Latency Secured) MAC
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Zigbee
PANC N1 N2 N3 N4Time
frame 1
PANC N1 N2 N3 N4Time
frame 2
PANC N1 N2 N3 N4Time
frame 3
PANC N1 N2 N3 N4Time
frame 4
Data Beacon
Data transmission is followed by beacon from PANC In each time frame 1-hop transmission is occurred Requirement of time frames are proportional to the
number of hops in the networks
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Adaptive S-MAC
ListenSleep
SYNC
1
3
4
Data
ACKCTS
RTS
2
SYNC
Source
Sink
Time Frame 1 Time Frame 2
Sleep Delay
Sleep Delay
SleepListen
SYNC
Data
ACKCTS
RTS
RTS
Listen
Data
ACKCTS
RTS
Data
ACKCTS
Data
ACKCTS
5RTS
Sync signal is transmitted at the starting of time frame
In each time frame 2-hops transmission is occurred
End to end Latency =½*Latency in Zigbee
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LE-MAC
ListenSleep
SYNC
1
3
4
Data
ACKCTS
RTS
2
Source
Sink
Time Frame 1
RTSData
ACKCTS
ACK
5
RTS
Data
ACKCTS Data
CTS
Listen
Data
ACKCTS
RTS
RTS
T-wakeup
Carriersensing
Carriersensing
Carriersensing
Sleep Delay
Sync signal is transmitted at the starting of time frame
In each time frame 4-hops transmission is occurred
End to end latency= ¼*Zigbee
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Sync-LS Protocol
N1
N2
N3
N4
Beacon +F. Data
Sleep Time
Sleep Time Sleep Time
Forward Time Frameof Sync-LS
Reverse Time Frame ofSync-LS
Single Time Frame of Sync-LS
Coordinator
Beacon
Data
Time frame is divided into two parts- Forward time frame- Reverse time frame
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Sync-LS Protocol In forward time frame, beacon and forward data are
transmitted up to end node To save energy, every node goes to sleep mode after forward
data transmission In reverse time frame, parent nodes transmit beacon to its
children nodes and receives the reverse data Transmission of beacon is controlled by the wakeup timer Wakeup timer is maintained by the following equation
Where, N= Maximum hop number, K= hop distance from edge node, tmargin= additional sleep time before reverse time frame, ∆tr = time interval between two reverse beacon, ∆tf = time interval between two forward beacon
frinmbfbr tktktkNtkNt )1()()( arg
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Comparison of Average Latency
1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
9
10
Lat
ency
[Sec
]
Hop distance
Sync-LS LE-MAC Adaptive S-MAC Zigbee
Sync-LS protocol provides lowest latency it requires a single time frame
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Comparison of Energy Consumption
1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
3.0
Ene
rgy
cons
umpt
ion
[mj]
Hop distance
Zigbee Sync-LS
Energy consumption depends on the modes of a sensor node
- Active mode (Transmission and Reception state)
- Sleep mode Energy consumption expressed by the
following equation
Where, n=number of nodes in the network, P t = power consumption per sec for data transmission, Tt = data transmission time, Pr = power consumption per sec for data reception or idle, Ta = active time
- Sleep mode energy consumption is neglected
Simulation result shows that energy consumption in Sync-LS is little higher than Zigbee because Sync-LS requires two beacons.
Thanks for Your Kind Attention
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