SMAC protocol

1
ECE/MAE 7750 Distributed Control SystemsFISP
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 Email abhishek_at_cc.usu.edu 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 NetworkApplications

• 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 http//www.intel.com/research/exploratory/
motes.htm
8
MAC ProtocolsExisting 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 802.11, CSMA
  etc.
• Scheduled based protocols e.g. TDMA, FDMA etc

9
MAC ProtocolsLimitations 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 802.11 (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
SMAC designFeatures

• Main features of SMAC include
• Periodic Listen
• Collision Avoidance
• Overhearing Avoidance
• Message Passing
• Tradeoffs

12
SMAC DesignPeriodic 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
13
SMAC DesignChoosing 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.

Border nodes with 2 schedule broadcast twice

• Broadcast the chosen schedule by sending out
  SYNC packet.

14
SMAC DesignListen and Sleep - Maintaining
Synchronization

• The listen time is divided into two parts
• For sending/receiving SYNC signal.
• For sending/receiving Data.

15
SMAC DesignAdaptive 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.

4
1
2
3
16
SMAC DesignOverhearing 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 designMessage 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.

Hidden terminal problem solved by ACK
C
SYNC
A
B
corrupt
18
SMAC DesignImplementation

• 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 802.11 like protocol without sleep
• SMAC without periodic sleep
• SMAC with period sleep

UCB mote with whip Antenna
19
SMAC DesignImplementation

• 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 DesignImplementation

• Tests on a ten hop network

The graph shows aggregate energy consumption in a
10-hop network
21
SMAC DesignConclusion

• 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
  http//www.intel.com/research/exploratory/motes.ht
  m