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Investigating Mac Power Consumption in Wireless Sensor Network

Investigating Mac Power Consumption in Wireless Sensor Network. Javier Bonny Supervised by Jun Luo. Contents. Introduction Source of energy waste Existing Solution S-MAC, B-MAC Our proposition Conclusion. Energy in WSN. Battery is the most critical resource

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Investigating Mac Power Consumption in Wireless Sensor Network

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

  2. Contents • Introduction • Source of energy waste • Existing Solution • S-MAC, B-MAC • Our proposition • Conclusion IC-29 – LCA – 02/09/2005

  3. 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

  4. 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

  5. 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

  6. S-MAC: Coordinated Adaptative Sleeping • Ye, Heidemann (USC), Estrin (UCLA) 2002 IC-29 – LCA – 02/09/2005

  7. 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

  8. Idle Listening avoidance • Periodic listen and sleep • Turn off radio when sleeping • Duty cycle is fixed (application dependant) Sleep Sleep Listen Listen Listen Listen Sleep Sleep IC-29 – LCA – 02/09/2005

  9. 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

  10. Overhearing Avoidance • Idea: Sleep when neighbors talk • Who should sleep? E C A B D F • 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

  11. 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

  12. B-MAC: Versatile Low Power MAC • Polastre, Hill, Culler (Berkeley), 2004 IC-29 – LCA – 02/09/2005

  13. 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

  14. B-MAC • Preamble sampling • Sender sends a long preamble to overlap with the receivers “carrier sense” duration. • Data transmission can use RTS/CTS or some other strategy. Receiver Sleep Sleep Data Rx Sender Preamble Data Tx IC-29 – LCA – 02/09/2005

  15. B-MAC • Duty cycle and preamble length are tunable • 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) Receiver Sleep Sleep Data Rx Check Interval Sender Preamble Data Tx IC-29 – LCA – 02/09/2005

  16. S-MAC vs B-MAC B-MAC is the MAC protocol chosen for TinyOS! IC-29 – LCA – 02/09/2005

  17. 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

  18. RTS Preambling IC-29 – LCA – 02/09/2005

  19. 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

  20. RTS Preambling IC-29 – LCA – 02/09/2005

  21. RTS Preambling • Advantage • Avoid overhearing • Preamble (RTSs, CTS, DIFS and SIFS) no longer than B-MAC preamble IC-29 – LCA – 02/09/2005

  22. 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

  23. 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

  24. Conclusion • That’s all Folks! Any question? IC-29 – LCA – 02/09/2005

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