This document presents S-MAC, an energy-efficient MAC protocol designed for wireless sensor networks. S-MAC aims to reduce energy consumption through the use of synchronized duty cycles where nodes periodically listen and sleep. It also supports self-configuration. The paper describes the characteristics of WSNs that require a different MAC approach than IEEE 802.11. Experiments show that S-MAC achieves significant energy savings of around 98% compared to IEEE 802.11 through the use of duty cycles and avoiding overhearing. However, S-MAC can introduce increased latency and may not perform as well as other protocols under heavy traffic loads. Tradeoffs between energy consumption and latency can be tuned by adjusting the duty cycle parameters.

1. By:
Presenter
Supervisor
An Energy-Efficient MAC
Protocol for Wireless
Sensor Networks

2. Topics
• Introduction
• S-MAC
• Experiment
• Conclusion
• Discussion
• Questions
2-25

3. • Wireless
Sensor
NetworksWSN
• MACProtocol
Overview
Topics
3-25
• PresentMAC
Design

4. WSN Applicatins
Application Specific
Wireless Networks
For Monitoring,
Smart Spaces,
Medical Systems
And Robotic
Exploration
And, Then
Large
Number Of
Distributed
Nodes And
Self
Organizing
So,
Normally
Battery
Operated
And Hence
Power
Limited
4-25

5. • Characteristics of WSNs: leading to a Medium/Media
Access Control MAC different from traditional wireless
MACs such as IEEE 802.11:
Use of battery-operated computing and sensing
devices.
devices collaborate for a common application such as
environmental monitoring.
WSNs are deployed in an ad hoc fashion, with nodes
remaining largely inactive for long time, but becoming
suddenly active when something is detected.
• In WSNs, Energy Conservation and Self-configuration
are primary goals, while Per-node Fairness and Latency
are less important.
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6. • Contention Based Protocols
 IEEE 802.11
• Distributed Coordination Function (DCF): high energy
consumption due to idle listening
 PAMAS
• Avoids the overhearing among neighboring nodes
• Requires Two Independent Radio Channels
• Does not address the issue of reduce Idle Listening
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7. Advantages
• Lower Energy Conservation when compared to
contention based as the duty cycle of the radio is
reduced and No Contention Overhead
Disadvantages
• Requires nodes to form real communication clusters
• Managing Inter-cluster Communication is difficult
• It is not easy to change the slot assignment
dynamically, hence Scalability is not as good as
contention based
• TDMA based protocols
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8. • Paper
Proposes
• S-MAC Goals
• Design
Considerations
Topics
8-25

9. • Paper Proposes
This paper proposes S-MAC (Sensor MAC) , a Medium/Media
Access Control (MAC) protocol designed for Wireless Sensor
Networks.
S-MAC here is based on the concept of the “Listen/Sleep Mode
Cycle” and is single-frequency contention-based protocol for
sensor networks.
• S-MAC Design Main Goals:
 First: Reduce Energy Consumption
 Second: Support Self-configuration
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10. Wastage Reducing of Energy from all Four
Sources Of Energy Inefficiency:
Collision
Overhearing
Control Overhead
Idle Listening
Using RTS and CTS
Switching the radio off when the
transmission is not meant for that node
Message Passing
Periodic Listen & Sleep
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11. 1. Energy efficiency
Often difficult Recharge batteries or replace them
Prolonging the Life-time is important
2. Scalability to the change in network size, node density
and topology
Some nodes may die over time
New nodes may join later
3. Other important attributes
i. Fairness
ii. Latency
iii. Throughput
iv. Bandwidth Utilization
11-25

12. •PART : A
•PART : B
•PART : C
Topics
12-25

13. • Test-bed
 Used Rene Motes as the development platform
and test-bed
 TinyOS
 3 working modes: Receiving, Transmitting And
Sleep
• Topology Used In The Experiment
 3 MAC modules on the mote and TinyOS platform
1. Simplified IEEE 802.11 (DCF)
2. Message Passing with Overhearing Avoidance (OA)
3. The complete (S-MAC)
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14. Listen time: 300 msec Sleeping time: 1 sec
SYNC: every 13 sec (10 listen/sleep period)
A, B, C use the same schedule
In each test, each source
periodically generates 10
messages, which in turn is
fragmented into 10 small
data packets supported by
the TinyOS.
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15. Heavy Traffic Light Traffic
Energy save due to avoiding
overhearing by using message
passing
Energy save due to
periodic sleep
802.11
OA
S-MAC
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Measured Energy Consumption In The Source Nodes

16.  If the message inter-arrival period is 5 seconds, a
message is generated every 5 seconds by each
source node, the S-MAC duty cycle does not impact a
lot when the inter-arrival time is less than 4 seconds.
 The traffic is heavy when the message inter-arrival
time is less than 4 seconds. In this case, 802.11 MAC
uses more than twice the energy used by S-MAC.
 One possible reason the problem of transfer SYNC
message.
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17. OA: In light traffic status, sources nodes keep
listening for quite a long time
OA
S-MAC
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Measured Percentage Of Time That The Source Nodes In The Sleep Mode

18.  Traffic load indeed changes over time. When
there is no sensing event, the traffic is very light.
 When some nodes detects an event, it may trigger
a big sensor like a camera, which will generate
heavy traffic.
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19. SYNC Overhead
Overhearing Avoidance still benefit
802.11
OA
S-MAC
Heavy Traffic Light Traffic
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Measured Energy Consumption In The Intermediate Node

20.  In node C:
• One reason is that S-MAC has synchronization
overhead of sending and receiving SYNC
packets.
• Another reason is that S-MAC introduces more
latency and actually uses more time to pass the
same amount of data.
 If the traffic is heavy: S-MAC does not perform
better than Overhearing Avoidance ( OA ).
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21. Topics
21-25
Is
this Protocol
convincing?
And, how
much so?

22. 2
1
3 Experiments show that the aimed results are SATİSFİED
 
This new MAC protocol has very good energy
conserving (~98%) compared with IEEE802.11.
S-MAC is an energy efficient mac protocol compared
to IEEE802.11
This new MAC protocol has the ability to make trade-offs
between energy and latency according to the traffic
conditions.
 S-MAC Trade-off between energy consumption and
latency can be easily tuned
22-25

23. • What is the
tradeoff by using
duty cycles?
• How can we make
the schedule
more intelligent?
23-25
Topics

24. • What is the tradeoff by using duty cycles?
 Channel utilization and throughput reduces/Latency increase
• How can we make the schedule more intelligent?
 Randomly select schedule is not enough. If a node “know” that there is a lot
of contention. It may extent the schedule when SYNC next time.
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• What are the disadvantages of S-MAC?
 Although S-MAC achieves low power operation, it doesn’t meet simple
implementation, scalability, and tolerance to changing network conditions.
As the size of the network increases, S-MAC must maintain an increasing
number of neighbors’ schedules or incur additional overhead through
repeated rounds of resynchronization.
 S-MAC suffers from the complexity and scaling problems.

25. Topics
1. Professional questionsdir
ectedtoDr.KunXie
2. Easy questions directed to
Me
25-25