Efficient MAC Protocols for Wireless Sensor Networks

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Efficient MAC Protocols for Wireless Sensor
Networks

• Mahendra Kumar

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Properties of a Well Defined MAC Protocol

• Energy Efficient
• Scalability
• Adaptability to changes in network topology
• Latency, throughput, bandwidth
• Fairness not so important

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Reason of Energy Waste

• Collision
• Overhearing
• Control Packet overhead
• Idle Listening
• Overremitting

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Existing MAC Protocols

• Sensor-MAC (S-MAC) Listen-sleep
• Timeout-MAC (T-MAC) Activation event
• WiseMAC Preamble Sampling

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S-MAC

• Main goal reduce power consumption
• Three major components
• Periodic sleep-listen
• Collision and overhearing avoidance
• Message passing

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Periodic Sleep-Listen

• Each node goes to sleep for some time,
• and then wakes up and listens to see if any
  other node wants to talk to it.
• During Sleep it turn off its radio.

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Collision and Overhearing Avoidance

• Interfering nodes go to sleep after they hear an
  RTS or CTS packet.
• Duration field in each transmitted packet
  indicates how long the remaining transmission
  will be.

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S-MAC
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Maintaining Synchronization

• The listen/sleep scheme requires synchronization
  among neighboring nodes.
• Updating schedules is accomplished by sending a
  SYNC packet.

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Advantages/Disadvantages

• Energy waste caused by idle listening is reduced
  by sleep schedules.
• Sleep and listen periods are predefined and
  constant which decreases the efficiency of the
  algorithm under variable traffic load.

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Timeout-MAC (T-MAC)

• Proposed to enhance the poor results of S-MAC
  protocol under variable traffic load.
• Listen period ends when no activation event has
  occurred for a time threshold TA.
• Reduce idle listening by transmitting all
  messages in bursts of variable length, and
  sleeping between bursts.
• times out on hearing nothing.

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S-MAC Vs T-MAC
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Advantages/Disadvantages

• Gives better result under variable load.
• Suffers from early sleeping problem node goes to
  sleep when a neighbor still has messages for it.

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WiseMAC

• All nodes defined to have two communication
  channels.
• Data channel uses TDMA
• Control channel uses CSMA
• Preamble sampling used to decrease idle listening
  time.
• Nodes sample the medium periodically to see if
  any data is going to arrive.

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WiseMAC
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Advantages/Disadvantages

• Dynamic preamble length adjustment results in
  better performance.
• Conflict when one node starts to send the
  preamble to a node that is already receiving
  another nodes transmission where the preamble
  sender is not within range. Hidden terminal
  problem

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Other MAC Protocols

• SIFT Event Driven
• TRAMA Traffic Adaptive MAC, TDMA Based

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