SMAC protocol

							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
                 Email: abhishek@cc.usu.edu
                   Date: February 02, 2005
Outline

   Introduction to Ad-hoc Wireless Sensor Networks
   The problem and existing solutions
   Introduction to S-MAC protocol
   S-MAC design
   Performance
   Conclusion
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
Ad-hoc Wireless Sensor Network
Applications
 Applications include
  Traffic Surveillance

  Military Applications

  Fire Detection

  Agricultural management
  Structure and Earthquake monitoring
  Industrial Control

  Rescue Operations
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.
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
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
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 802.11, CSMA etc.

     Scheduled based protocols e.g. TDMA, FDMA etc
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 802.11 (Contention based protocol)
     Each node contends for the medium as necessary

     Major drawback: Wastes a lot of energy in idle listening
SMAC Protocol
Introduction

   Stands for Sensors Medium Access Control
   Specifically designed for Ad hoc wireless sensor networks
   Primary goal: Energy Efficiency
SMAC design
Features
 Main features of SMAC include
    Periodic Listen
    Collision Avoidance
    Overhearing Avoidance
    Message Passing

 Tradeoffs

          Latency
                                 Energy
          Fairness
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
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 1                                       Border nodes with 2
                                         Schedule 2         schedule broadcast twice


        Broadcast the chosen schedule by sending out SYNC packet.
SMAC Design
Listen and Sleep - Maintaining Synchronization

   The listen time is divided into two parts:
     For sending/receiving SYNC signal.

     For sending/receiving Data.
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
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.
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       DATA/ACK         DATA/ACK              DATA/ACK


                             Unfairness                Contention for medium

    Hidden terminal problem solved by ACK
                                                               C
                                                    SYNC

            A         DATA         B      corrupt
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 802.11 like protocol without sleep
       SMAC without periodic sleep
       SMAC with period sleep




        UCB mote with whip Antenna
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
SMAC Design
Implementation
 • Tests on a ten hop network




 The graph shows aggregate energy consumption in a 10-hop network
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.
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.htm