OMAC: A Receiver Centric Power Management Protocol

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O-MAC A Receiver CentricPower Management
Protocol

• Hui Cao, Kenneth W. Parker, Anish Arora

The Ohio State University, The Samraksh Company
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Outline
1. Receiver centric design 2. Energy efficiency
comparison 3. O-MAC protocol design
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Part I Receiver Centric Design
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Dominant Receiver Power Consumption
One typical surveillance application
Receiver Radio 2100 J/day
Intelligent Alarms
Signal processing 60 J/day
Everything else 8 J/day

• Large portion of energy is consumed in receiver
  radio

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Increasing Rx Power Consumption
This trend is due to 1) Low SNR 2)
Sophisticated receiver computation
Despreading Forward-Error Correction (FEC)
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Receiver Centric vs. Transmitter Centric

• Transmitter Centric MAC design
• Transmitter implicitly knows receiver will wakeup
  during transmission
• Collision avoidance is transmitter driven (i.e.,
  RTS-CTS, CCA)

Transmitter
Receiver
Transmitter

• Receiver Centric MAC design
• Receiver explicitly communicates its wakeup
  schedule to transmitter
• Collision avoidance is receiver driven (i.e.,
  receivers use TDMA)

Receiver
Transmitter
Receiver
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Why Receiver Centric Design?

• Historically, MAC design has focused on
  Transmitter Efficiency
• However, dominant cost of receiver radio has
  implied that

Goodput
0.02
Receiver Efficiency
Receiver Power Consumption
Goodput
0.5
Transmitter Efficiency
Transmitter Power Consumption
Goodput
0.02
Total Energy Efficiency
Transmitter Receiver Power Consumption

• We claim Receiver Centric approach yields
  substantially higher Receiver Efficiency

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Part II Energy Efficiency Comparison
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Assumptions and Notations

• Traffic model
• Uniform random traffic
• Notations
• E energy efficiency

Goodput (Msgs Sent Receive)
Total (Msgs Sent Receive)
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Theoretical Energy Efficiency

• Well consider
• Synchronous Blinking (S-MAC, T-MAC)
• Long Preamble (B-MAC, WiseMAC)
• Asynchronous Wake-up
• Random Time-Spreading
• Staggered On
• Pseudo-random Staggered On

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Synchronous Blinking (e.g. S-MAC T-MAC)

• Wakeup schedule
• All the nodes wake up simultaneously
• Major drawbacks
• Idle listening
• Overhearing
• Limiting the channel capacity

Result
? number of interfering nodes e natural
exponential base
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2) Long Preamble (e.g. B-MAC, WiseMAC)

• Wakeup schedule
• Each node wakes up asynchronously
• Major drawbacks
• Case 1
• Overhearing
• Case 2
• Idle listening
• Blank out one frame

Result
? duty cycle
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3) Asynchronous Wakeup

• Wakeup schedule
• Each node wakes up with fixed schedule
• For a frame length n slots
• Only slots are needed to wake
  up
• Major drawbacks
• Mainly Idle listening
• Overhearing

Result
? duty cycle
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4) Random Time Spreading

• Wakeup schedule
• In each time slot, each node
• wakes up randomly with
• probability p
• Major drawbacks
• Mainly Idle listening
• Overhearing

When p 0.5
Result
? number of interfering nodes
? duty cycle
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5) Staggered On

• Wakeup schedule
• Only one receiver wakes up in the interference
  region at one time
• Scheduled globally to avoid receiver collision
• Major drawbacks
• Global schedule
• Have to maintain neighbor list

Result
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6) Pseudo-random Staggered On

• Wakeup schedule
• In each time frame, each node wakes up at a
  pseudo-random slot.
• Each node knows its neighbors wakeup slot by
  storing the random seed and steps.
• Major drawbacks
• Have to maintain neighbor list

Result
r is a factor near 1
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Energy efficiency comparison
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Part III O-MAC Protocol Design
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O-MAC Protocol Design

• Based on Pseudo-random Staggered On

• The Core Protocol
• Interfaces
• Neighbor list
• Send
• Receive
• Synchronous ACK
• Pseudo-random Scheduler

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O-MAC Analysis and Simulation

• Simulation confirms theoretical analysis
• Maximal energy efficiency for particular traffic
  load!
• ?Adaptive duty cycle

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O-MAC Key Implementation Issues

• Time Synchronization
• Current technique
• lt 10 PPM
• Every 2 minutes, to guarantee 1ms accuracy
• Cost 0.001 duty cycle

Sender Centric Application
Receiver Centric Communication

• Adaptive Duty Cycle
• A cross layer design issue

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Conclusion and Future work

• Conclusion
• Receiver Centric has substantial impact on power
  management
• Receiver vs. Transmitter Collision Avoidance
• OMAC has been implemented and is being integrated
  for mobile sensor network experiments on Dec.7 at
  OSU

• Future work
• Receiver Centric higher layer protocol
• (Network, Transport, Application)
• Adaptive duty cycle scheme