Transcript Slide 1
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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