1. Presenter: Abhishek Gupta Dept. of Electrical and Computer Engineering
ECE/MAE 7750: Distributed Control Systems FISP: Focused Independent Study and Presentation
SMAC Protocol With Coordinate Sleeping for Ad-hoc Wireless Sensor Networks
Presenter: Abhishek Gupta
Dept. of Electrical and Computer Engineering
Utah State University
Date: February 02, 2005

2. Outline Introduction to Ad-hoc Wireless Sensor Networks
The problem and existing solutions
Introduction to S-MAC protocol
S-MAC design
Performance
Conclusion

3. Introduction to Ad-hoc Wireless Sensor Networks
An Ad Hoc wireless sensor network is a network of sensor devices that are deployed in an ad hoc fashion and coordinate for sensing a physical phenomenon.
Each wireless sensing node typically includes
A Sensor
A processor
A radio
A battery

4. Ad-hoc Wireless Sensor Network Applications
Applications include
Traffic Surveillance
Military Applications
Fire Detection
Agricultural management
Structure and Earthquake monitoring
Industrial Control
Rescue Operations

5. Attributes of Ad hoc Wireless Sensor Networks
Extremely power efficient
Batteries die over time
Cost of recharging nodes may exceed the cost of node itself.
Insensitive to change in network topology and node density.
New nodes can be added
Existing nodes can be relocated
Efficient use of bandwidth.
Fairness can be compromised for energy efficiency.
Inter-network data processing
Sending raw data to some end node for processing consume more energy.

6. Energy Efficiency in Ad hoc Wireless Sensor Networks
Energy efficiency is the primary concern in a wireless sensor networks.
Causes of energy waste
Collisions
Takes place at the receiver
Increases Latency
Overhearing
Happens when the nodes pick up data destined to other nodes
Idle Listening
Listening to traffic that is not sent

7. Energy Efficiency in Ad hoc Wireless Sensor Networks
Motes, which are used as nodes in wireless sensor networks, work on extremely low energy !!!
Source:

8. MAC Protocols Existing Solution
Stands for Medium Access Control.
Determine when and how nodes should access the shared medium.
Two broad categories
Contention based protocols e.g. IEEE , CSMA etc.
Scheduled based protocols e.g. TDMA, FDMA etc

9. MAC Protocols Limitations of Existing Solution
TDMA (Scheduled protocol)
Each node gets full bandwidth for a pre-allocated time in turns
Major drawback: Not suitable for networks whose node density changes.
FDMA (Scheduled protocol)
Each node gets a permanent share of bandwidth
Major drawback: Poor bandwidth utilization
IEEE (Contention based protocol)
Each node contends for the medium as necessary
Major drawback: Wastes a lot of energy in idle listening

10. SMAC Protocol Introduction
Stands for Sensors Medium Access Control
Specifically designed for Ad hoc wireless sensor networks
Primary goal: Energy Efficiency

11. Latency Fairness Energy SMAC design Features Periodic Listen
Main features of SMAC include
Periodic Listen
Collision Avoidance
Overhearing Avoidance
Message Passing
Tradeoffs
Latency
Fairness
Energy

12. SMAC Design Periodic Listen and Sleep
Problem: Idle listening consumes significant energy
Solution: Put all the nodes to sleep periodically
Turn off radio when sleeping
Reduce duty cycle to ~10%
Preferable, neighboring nodes follow same schedule
Latency
Energy

13. SMAC Design Choosing and Maintaining Schedule
Nodes exchange their schedule by periodically broadcasting SYNC packet
Nodes take following 2 steps to choose their schedule
Listen for SYNC packets for a fixed amount of time
Case 1: No SYNC packets are received
Case 2: SYNC packet is received.
Case 3: Multiple SYNC packets are received.
Schedule 2
Schedule 1
Border nodes with 2 schedule broadcast twice
Broadcast the chosen schedule by sending out SYNC packet.

14. SMAC Design Listen and Sleep - Maintaining Synchronization
The listen time is divided into two parts:
For sending/receiving SYNC signal.
For sending/receiving Data.

15. SMAC Design Adaptive listening
Used to reduces multi-hop latency due to periodic sleep.
Neighboring nodes wake up for a short period of time at the end of each transmission. 1 2 3 4
RTS
CTS
CTS

16. SMAC Design Overhearing Avoidance
All immediate neighbors of sender and receiver are put to sleep upon receiving RTS/CTS.
Neighbors do not overhear data packets and following ACKS.
The duration field in the packet indicates how long to sleep.

17. SMAC design Message Passing
SMAC reintroduces the concept of Message Passing
Long messages are converted into small fragment and are transmitted in bursts.
Receiver acknowledges each received fragment.
DATA/ACK
Contention for medium
Unfairness
Hidden terminal problem solved by ACK C
SYNC A B
DATA
corrupt

18. SMAC Design Implementation
To demonstrate the effectiveness of SMAC protocol compared to conventional protocols, they were implemented and tested on Motes.
Operating System used was TinyOS.
Three MAC modules were implemented on Rene Motes
An like protocol without sleep
SMAC without periodic sleep
SMAC with period sleep
UCB mote with whip Antenna

19. SMAC Design Implementation
Tests on a two hop network
Measures total energy overtime to send messages
Idle listening rarely happens
Periodic sleep for Idle listening
The graph shows the mean energy on radios of source nodes

20. SMAC Design Implementation
Tests on a ten hop network
The graph shows aggregate energy consumption in a 10-hop network

21. SMAC Design Conclusion
SMAC offers significant energy efficiency over always listening MAC protocols.
SMAC is able to greatly prolong the network life, which is critical for real-world network applications.

22. References:
Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks, by Wei Ye, John Heidemann, and Deborah Estrin (IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 12, NO. 3, JUNE 2004 )
Presentation by Wei Ye on MAC Layer Design for Wireless Sensor Networks
Presentation by Ranjith Udayshankar on Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks
Figure of motes power spectrum obtained from