Investigating Mac Power Consumption in Wireless Sensor Network Javier Bonny Supervised by Jun Luo

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Contents

     Introduction Source of energy waste Existing Solution  S-MAC, B-MAC Our proposition Conclusion IC-29 – LCA – 02/09/2005

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Energy in WSN

   Battery is the most critical resource It is important to reduce the waste of energy to improve network lifetime How to improve energy efficiency  Routing    Mobile Base Station Energy efficient MAC protocol … IC-29 – LCA – 02/09/2005

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MAC Attributes for WSN

    Energy efficiency Collision avoidance  Basic task of a MAC protocol Scalability and adaptability  Network size, node density and topology change Secondary concerns  Latency    Channel utilization Throughput Fairness IC-29 – LCA – 02/09/2005

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Source of energy waste (MAC)

    Idle listening  Node listens to an idle channel Overhearing  Node listens for a message sent to another node Collision  Two nodes emit at the same time and messages must be retransmitted Control packet overhead  Required frame header and signaling to implement the MAC IC-29 – LCA – 02/09/2005

S-MAC: Coordinated Adaptative Sleeping

 Ye, Heidemann (USC), Estrin (UCLA) 2002 6 IC-29 – LCA – 02/09/2005

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S-MAC

 Reducing the waste of energy:  Idle listening: by Periodic Sleep   Overhearing: by switching the radio off when the transmission is not meant for that node Collision: by using RTS and CTS IC-29 – LCA – 02/09/2005

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Idle Listening avoidance

 Periodic listen and sleep

Listen Sleep Listen Sleep Listen Sleep Listen Sleep

  Turn off radio when sleeping Duty cycle is fixed (application dependant) IC-29 – LCA – 02/09/2005

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Choosing and Maintaining Schedules

  Each node maintains a schedule table that stores schedules of all its known neighbors.

Periodic timer synchronization among neighbors are needed to prevent the clock drift.

IC-29 – LCA – 02/09/2005

Overhearing Avoidance

  Idea: Sleep when neighbors talk Who should sleep?

E C A B D F 10   All immediate neighbors of sender and receiver How long to sleep?

 The duration field in each packet informs other nodes the sleep interval IC-29 – LCA – 02/09/2005

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SMAC: Pros and Cons

  Pros   Significant low power operation Schedules sleep and transmit times to enable low power data transfer with reasonable-latency.

Cons  Implementation is quite complex for WSN    Significant state maintenance (schedules) Neighbors synchronization Sleep and listen period are predefined and constant (not efficient for variable traffic load) IC-29 – LCA – 02/09/2005

B-MAC: Versatile Low Power MAC

 Polastre, Hill, Culler (Berkeley), 2004 12 IC-29 – LCA – 02/09/2005

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B-MAC

  Unscheduled sleep  Reduces control overhead  But sender incurs greater overhead to wakeup unsynchronized receiver from sleep (long preamble) Unscheduled wakeup  Keep wakeup intervals very short  CSMA/CA or some other app-specific scheme can be used IC-29 – LCA – 02/09/2005

B-MAC

 Preamble sampling

Receiver Sleep Sleep Sender Preamble Data Rx Data Tx

  Sender sends a long preamble to overlap with the receivers “carrier sense” duration.

Data transmission can use RTS/CTS or some other strategy.

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B-MAC

 Duty cycle and preamble length are tunable

Receiver Sleep Sender

Check Interval

Sleep Preamble Data Rx Data Tx

15     Preamble length ≥ Check interval Long sleeping time trades transmission latency for low power consumption (suitable for sparse transmission) A long preamble increases the power consumption of all nodes in the sender’s transmission coverage due to overhearing Sender and Receiver should be tuned together (Loose Sync) IC-29 – LCA – 02/09/2005

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S-MAC vs B-MAC

Solve Idle Listening Solve Overhearing Synchronisation needed Simplicity/scalability Overall performance S-MAC yes yes Yes no good B-MAC yes no less yes better B-MAC is the MAC protocol chosen for TinyOS!

IC-29 – LCA – 02/09/2005

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Our proposition: RTS Preambling

  Take the best of both world  Based on B-Mac + add Overhearing avoidance Idea  Send useful information (RTS) in the preamble instead of a constant IC-29 – LCA – 02/09/2005

RTS Preambling

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RTS Preambling

 Comments  Basic rule: if you hear something while listening, listen until the end   Listening period (duty cycle) > DIFS What to do during SIFS period?

 Turn off radio or continue listening?

 It depends on the Radio performance!

IC-29 – LCA – 02/09/2005

RTS Preambling

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RTS Preambling

 Advantage  Avoid overhearing  Preamble (RTSs, CTS, DIFS and SIFS) no longer than B-MAC preamble IC-29 – LCA – 02/09/2005

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RTS Preambling

  Our proposal is good for unicast We must use an alternative for broadcast, multicast  Repeat message in the preamble (like WiseMAC) IC-29 – LCA – 02/09/2005

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Conclusion

  We think RTS Preambling could improve B-MAC performance… To do  Figure out how to set the NAV   Finalize alternative for broadcast Finish implementation  Simulation + comparison… IC-29 – LCA – 02/09/2005

Conclusion

 That’s all Folks!

Any question?

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