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Energy efficient S-MAC protocol for Wireless Sensor Networks

Presented by:Priyanka F. Hongal 1st sem, MTECH, GIT, BELGAUM

Guide

Prof. N.S.Sirdeshpande

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Outline

Definition Wireless sensor networks Power consumption Energy efficient MAC protocols S-MAC: an energy-efficient MAC protocol for wireless

sensor networks Conclusion

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Definition

Energy efficient

– Anything that consumes less power in order to work effectively.

S-MAC protocol

– MAC protocol especially for sensor networks.

Wireless Sensor Networks

– Networks that are composed of a large number of sensor nodes, which are densely deployed either inside the phenomenon or very close to it.

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Wireless sensor networks

Sensor nodes are low cost, low power, multifunctional electronic devices.

Small in size

Wireless communication over short distances.

Sensors have Sense, data processing and communicating components.

A sensor network is composed of densely deployed sensor nodes.

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Applications

Military

Military command, control, communications, computing intelligence, targeting systems.

Health

Monitor patients, assist disabled patients.

Others

Managing inventory, monitoring product quality, monitoring disaster areas.

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Protocol stack

Physical layer -Addresses simple but robust modulation, transmission and receiving techniques.

Data Link Layer -Is responsible for multiplexing of data streams, data frame detection, medium access and error

control. -Medium access control MAC a sub-layer.

Network Layer -Routes data supplied by transport layer.

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Protocol stack (contd…)

Transport Layer - maintains flow of data

Application Layer -depends on sensing tasks

Power Management Plane -manages how sensor node uses its power

Task M

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Transport Layer

Network Layer

Data Link Layer

Physical Layer

Application layer

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Protocol stack (contd…)

• Mobility Management Plane

-detects and registers node movement

Task Management Plane

-balances and schedules sensing tasks given to a specific region

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Power consumption

Wireless sensor node is an microelectronic device can be equipped with limited power source.

Replenishment of power resource might be impossible, sensor lifetime shows a strong dependence on battery lifetime.

Power consumption is divided into 3 domains Sensing Communicating Data processing.

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Power consumption (Contd..)

Major sources of energy waste

Collision

Idle listening

Overhearing

Control packet overhead

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MAC Requirements in Sensor networks

Collision avoidance Energy efficiency Scalability & Adaptivity

Latency Fairness Throughput Bandwidth utilization

Primary

Secondary

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Energy efficient MAC protocols

S-MAC

T-MAC

TRAMA

Power efficient System

Cluster Based energy efficient scheme

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Sensor MAC Protocol (S-MAC)

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S-MAC protocol design

Reduce energy consumption

Support good scalability and collision avoidance

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Tries to reduce wastage of energy from all four sources of energy inefficiency

Collision – by using RTS and CTS Overhearing – by switching the radio off when the transmission is not meant for that node Control overhead – by message passing Idle listening – by periodic listen and sleep

S-MAC protocol design

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Features of S-MAC

Periodic listen and sleep

Collision and Overhearing avoidance

Message passing

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Periodic Listen and Sleep

Basic scheme

– Duration of sleep and listen time can be selected based on the application scenario

– To reduce control overhead, neighboring nodes are synchronized (i.e. Listen and sleep together)

Listen Sleep Listen Sleep

time

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Periodic Listen and Sleep

Neighboring nodes A and B have different schedules. They synchronize with nodes C and D respectively

C A B D

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Periodic Listen and Sleep

– If a node A wants to talk to node B, it just waits until B is listening

– If multiple neighbors want to talk to a node, they need to contend for the medium

– Contention mechanism is the same as that in IEEE 802.11 (using RTS and CTS)

– After they start data transmission, they do not go to periodic sleep until they finish transmission

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Choosing and Maintaining Schedules

Each node maintains a schedule table that stores schedules of all its known neighbors

To establish the initial schedule (at the startup) following steps are followed:

– A node first listens for a certain amount of time– If it does not hear a schedule from another node, it randomly

chooses a schedule and broadcast its schedule immediately– This node is called a SYNCHRONIZER

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Choosing and Maintaining Schedules

If a node receives a schedule from a neighbor before choosing its own schedule, it just follows this neighbor’s schedule

This node is called a FOLLOWER and it waits for a random delay and broadcasts its schedule

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Maintaining Synchronization

for SYNC for RTSReceiver

Listen

Sleep

Sender 1

Sender 2

Sender 3

SYNC

SYNC

CS

CS

CSCS

Sleep

RTS

RTS

Send data if CTS received

Send data if CTS received

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Collision and Overhearing Avoidance

Collision Avoidance– Using RTS/CTS

Overhearing Avoidance– Set timer using NAV– If timer is not zero, a node go to sleep

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Message Passing

Transmitting a long message as a packet is disadvantageous as the re-transmission cost is high

Fragmentation into small packets will lead to high control overhead as each packet should contend using RTS/CTS

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Message Passing

Solution– Fragment message in to small packets and transmit them as

a burst Advantages

– Reduces latency of the message– Reduces control overhead

Disadvantage– Node-to-node fairness is reduced, as nodes with small

packets to send has to wait till the message burst is transmitted

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S-MAC Conclusions

Advantages:– Periodically sleep reduces energy consumption in idle

listening– Sleep during transmissions of other nodes– Message passing reduces contention latency and control

packet overhead

Disadvantages:– Reduction in both per-node fairness & latency

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References

I.F. Akyilidiz and W.Su and Y. Sankarsubramaniam, “ A Survey on Sensor Networks,” in IEEE Communications Magazine, August 2004.

“Wireless LAN Medium Access Control(MAC) and Physical Layer(PHY) Specifications.” IEEE 802.11 Standards, 1997.

I. Demirkol, C. Ersoy, and F. Alagoz, “MAC Protocols for Wireless Sensor Networks: a survey,” IEEE Communication magazine, vol. 44, no. 4, pp. 115-121, April 2006.

W. Ye and J. Heideman, “Medium Access Control in Wireless Sensor Networks,” in USC/ISI Technical Report, ISI-TR-580, 2003.

T.V Dam and K. Langendeon, “An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,” in The First ACM Conference on Embedded Networked Sensor Systems, 2003

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Questions and comments