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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

Large portion of energy is consumed in receiver radio

One typical surveillance application:

Receiver Radio~2100 J/day

Signal processing ~60 J/day

Everything else ~8 J/day

Receiver Radio

Signal Processing

Other

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Increasing Rx Power Consumption

Rx becomes higher than Tx!with evolution of Berkeley motes

3.8

9.6

19.7

12

16.5 17

0

5

10

15

20

25

TR1000 (Mica 2001) CC1000 (Mica2 2002) CC2420 (Telos 2004)

mA

Rx Power Tx Power

0

5

10

15

20

25

30

35

40

Freescale MC12192 OKI ML7222 Ember EM250

mA

Rx Power Tx Power

Other popular radio chips also have higher Rx power consumption

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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)

Receiver Centric MAC design:• Receiver explicitly communicates its wakeup schedule to transmitter

• Collision avoidance is receiver driven (i.e., receivers use TDMA)

TransmitterReceiver

TransmitterReceiver

Transmitter

Receiver

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Why Receiver Centric Design?

We claim: Receiver Centric approach yields substantially higher Receiver Efficiency

Receiver Efficiency ≈ Total Energy Efficiency ≠ Transmitter Efficiency

Receiver Efficiency = Goodput

Receiver Power Consumption

Transmitter Efficiency = Goodput

Transmitter Power Consumption

Total Energy Efficiency = Goodput

Transmitter + Receiver Power Consumption

Historically, MAC design has focused on Transmitter Efficiency

However, dominant cost of receiver radio has implied that

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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

)( j

iji

ji

RS

ME

Goodput (Msgs Sent + Receive)

Total (Msgs Sent + Receive)

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Theoretical Energy Efficiency

We’ll 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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Frame

Slot Slot

Frame

SlotSlotSlot Slot Slot Slot

Listen

Transmit

Sleep

Frame

Slot Slot

Frame

SlotSlotSlot Slot Slot Slot

Sender

Receiver

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

1

74.0

)1(

2max

e

E : number of interfering nodes

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2) Long Preamble (e.g. B-MAC, WiseMAC)

Case 2: Multiple Repeat Packets

Listen

Transmit

Sleep

Slot Slot

Slot Slot

Sender

Receiver

Slot Slot

Frame

Frame

SlotSlot

Slot

Sender

Slot

Slot Slot

Receiver

Slot Slot

Preamble

Case 1: Single Packet

2max

E : duty cycle

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3) Asynchronous Wakeup

Sender

Frame

Slot Slot

Receiver

Listening

Transmission

Sleep

SlotSlot Slot Slot Slot

Frame

Slot Slot SlotSlot Slot Slot Slot

2max E : duty cycle

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4) Random Time Spreading

In each time slot, each node wakes up randomly No time sync

Power efficiency:

2

max E : duty cycle

: number of interfering nodes

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5) Staggered On

43.0max E

Only one receiver wakes up in the interference region at one time

Scheduled globally to avoid receiver collision

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6) Pseudo-random Staggered On

Frame

Slot Slot

Frame

SlotSlotSlot Slot Slot Slot

Listen

Transmit

Sleep

Frame

Slot Slot

Frame

SlotSlotSlot Slot Slot Slot

Sender

Receiver

rE *43.0max r is a factor near 1

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Energy efficiency comparison

10 15 20 25 30 35 40 45 500

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

The average number of nodes that interfere

The

ene

rgy

effic

ienc

y

Staggered On

Pseudo-random Staggered On

Long PreambleSynchronous Blinking

Asynchronous Wake-up

Random Time Spreading

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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

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

The transmission probability when one neighborhood receiver is on (ptm

)

The

ene

rgy

effic

ienc

y

Energy efficiency-simulation

Energy efficiency-theoretical1. Simulation confirms

theoretical analysis

2. Maximal energy

efficiency for

particular traffic load!

Adaptive duty cycle

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O-MAC Key Implementation Issues

Time Synchronization• Current technique:

• < 10 PPM

• Every 2 minutes, to guarantee 1ms accuracy

• Cost: 0.001% duty cycle

Adaptive Duty Cycle• A cross layer design issue

Sender Centric

Application

Receiver Centric

Communication

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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