BWRC

Chunlong Guo, Prof. Jan Rabaey

Low Power MAC for Ad Hoc Wireless Network

EECSUniversity of California at Berkeley

BWRC

Outline• Media Access and Existing Solutions

• MAC for PicoNode Overview

• Multi-Channel MAC and Distributed Algorithm

• Sleeping Mode Based on Ultra Low Power Wakeup Radio

• Future Research, Design Methodology and Environment, Status and Time Line

BWRC

Wireless Media Access Control

MAC: Let multiple radios share the same communication media.

Time

Code

Freq

uen

cyPhysical

MACNetwork

Application

• Local Topology Discovery and Management.• Media Partition By Allocation or Contention.• Provide Logical Channels to Upper Layers.

BWRC

Media Access in Multi-hop Networks

• Large number of short range radios in a wide area Transmission Locality

Problems: Good thing: Channel Reuse

Hidden Terminal, (CSMA is not appropriate)No Global Synch.

AB C

ED

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Solution 1: Contention BasedMACA: [p. Kam, 90]

RTS-CTS-DATAMACAW: [V. Bharghavan, 1994] add link layer ACK.FAMA [C.L. Fuller, 95] 802.11: Add carrier sensing Optional ACKPAMAS: [S. Singh, 2000] Power aware MAC Separate signaling channel

RTS

CTS

RTS

Collision at B

Collision still exists. Too much overhead.

A B C D

collide

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Solution 2: UCLA Allocation Based• Localized Central Control: Cluster• Self-elected Cluster Head.• Neighboring Clusters Use Different Codes• Same Code, TDMA Inside Cluster• Virtual Circuit: QoS Support

Unstable Cluster StructureToo much Management Overhead

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PicoMAC ? Why Not Just Pick One?

• Most existing MACs are Targeted for One-hop, centralized control network: cellular network,

802.11, Bluetooth… Bandwidth hungry application, strict QoS requirement.

• Existing MACs are Based on Existing Radio’s More than 90% of power is burned when radio is idle.

‘Low power’ System Built on Existing MAC is NOT Low Power

BWRC

Opportunities for PicoMAC

• Application Driven, Low Duty-Cycle MAC

• New Radio Architectures

• Vertically-Integrated Interactive Design Methodology

PHY

MAC

ApplicationNetwork

BWRC

Outline• Media Access and Existing Solutions

• MAC for PicoNode Overview

• Multi-Channel MAC and Distributed Algorithm

• Sleeping Mode Based on Ultra Low Power Wakeup Radio

• Future Research, Design Methodology and Environment, Status and Time Line

BWRC

PicoNode ≠ MultiMedia• Low-date Rate Radio : 10kbps (peak)

• Low Traffic Duty Cycle: ~ 1%, 1~200 Bytes/source/s

• Short Packet: <50Bytes

• Loose QoS Requirements, Often not Delay Sensitive

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Design Goal• Primary Goal: energy / useful bit (EPB)

• Scalability: both in global sense of network size and local sense of nodes density

• Distributed Protocol: to achieve a robust and self-configuring network.

• Mobility: limited number of mobile nodes, with limited speed.

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Where Energy Goes?

When idle: Channel MonitoringCollision and Retransmission Signaling overhead (header, control pkts)

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Low Power MAC for PicoNode

Spread Spectrum Multi-Channel SchemeTo Reduce Collision RateTo Reduce Signaling Overhead (Shrink Address Space)

Deep-Sleep Mode with Wakeup RadioPower Down the Whole Data RadioReduce Monitoring Energy Consumption by 103 Times

Adaptive Mobility Support

BWRC

Outline• Media Access and Existing Solutions

• MAC for PicoNode Overview

• Multi-Channel Scheme and Distributed Algorithm

• Sleeping Mode Based on Ultra Low Power Wakeup Radio

• Future Research, Design Methodology and Environment, Status and Time Line

BWRC

CDMA Multi-Channel Scheme

• Parallel Transmission without Synch.• Implicit Local Address: Channel

Idea: Nodes use different channels to transmit data, no collision at receiver.

Key: Locally Unique with Global Reuse

1

3

2

4

5

6 7

8

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Multiple Channel Assignment• Sender based CANo primary collision

Receiver need switch data channels

Needs a separate signaling channel

• Receiver based CAPrimary collision

Receiver only listen to its own channel

No need signaling channel

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Find the Solution: Graph Coloring

• Goal: For any node, all its neighbors are with different colors

• Or: All two-hop neighbors with different colors.

• Number of colors needed:#(NCA) <= min {d(d-1)+1, |v|}

Brook and Vizing theorem

Model:An incomplete graph

G = (V,E)d is the maximum degree of

nodes

1

2

3

4

5

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Performance AnalysisModel: a ∆-regular graphp: traffic density

SC (Share Single Channel ): Bsca = p (1-p) (∆-1) (1-p)

RCA (Send on Receiver’s Channel ): Brca = p (1-p/∆) (∆-1) (1-p)

TCA (Send on Sender’s Channel ): Btca = p [1-(1-p/∆) ∆ ](1-p)

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CA Performance Analysis

SC

TCARCA

SC

TCARCA

BWRC

Outline• Media Access and Existing Solutions

• MAC for PicoNode Overview

• Multi-Channel MAC and Distributed Algorithm

• Sleeping Mode Based on Ultra Low Power Wakeup Radio

• Future Research, Design Methodology and Environment, Status and Time Line

BWRC

Power Down Data Radio• Current Radio Sleeping Mode: 10~50% Power

Consumption• For PicoNode Running at 1% Duty Cycle, 90~95%

Energy When Radio Is Idle.

• Even Worse As PicoNode Radio Is Shorter Range

150mW50mWBWRC TCI

0.18W1.48W3WLucent WaveLAN 23dBm 915MHz

0.18W1.8W1.825WLucent WaveLAN 15dBm 915MHz

0.05W0.6W1.8WDEC Plessey DE 6003 2.4GHz

StandbyReceiveTransmit

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Sleeping mode signaling• Problem: How To Send Data To a Sleeping

Node?

• Solution: Scheduling Wakeup Reactive wakeup: Sender Send Beacon

• PicoNode chose to do reactive wakeup

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Wake-up Radio• Always running

Super low power: 10-4~ 10-3 active mode power

• Data radio shut down when idle, and powered up by wake-up radio

• Broadcast and uni-cast mode• Receiver response time: <10ms

D/APowerAmplifier X

ED PPD

Data/control codesWakeup Tone

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Wakeup Sequence and Energy Profile

Node B

DATA

ACK

Useful dataPower Profile

WUP

CTS

E(useful data traffic) + E(overhead traffic) + E(idle)EPB =L(useful data traffic) * [1-p(collision)]

TwTr Th

Node A

BWRC0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Traffic Rate (10kbps)

Ene

rgy

Per

Bit

(mJ/

bit)

Lp = 20 Lp = 60 Lp = 100Lp = 140Lp = 180Lp = 220Lp = 260Lp = 300

EPB Performance AnalysisTotal Number of Nodes

N=100Network Dimention

D = 6Number of Channels

M = 32Radio Bit Rate

R=10kbps

Pt =2mw

Pr =3mw

Pm = 2mw

Ps = 1uW

Lp = 20bits

Lp = 60bits

Lp = 300bits

BWRC0 0.05 0.1 0.15 0.2 0.25 0.3

100

101

102

Traffic Density (10kbps)

EP

B (u

W/b

it)

Ps=1uW Ps=100uWPs=1mW

EPB Performance Analysis

Ps = 1uWPs = 100uW

Ps = 1mW

Conclusion:For duty cycle 1~10 percent:

10 ~ 100 times better

BWRC

Outline• Media Access and Existing Solutions

• MAC for PicoNode Overview

• Multi-Channel MAC and Distributed Algorithm

• Sleeping Mode Based on Ultra Low Power Wakeup Radio

• Future Research, Design Methodology and Environment, Status and Time Line

BWRC

Things To Be Addressed• Topology Control

Equal Transmission Power, Results in Bad Connectivity• Proposed Solution: Link-based Transmission Power

Management to reach a ‘good’ network connectivity Power, Traffic Aware

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 300

5

10

15

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Design Flow & Environment

AlgorithmExploration/Evaluation

System SimulationPerformance Evaluation

SDLFunctionalVerification

Documentation

Test-BenchPrototyping

Measurements

System DefinitionAbstraction

VCCArchitectureExplorationEvaluation

I II

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Conclusion• Create General-Purpose Tools and Vertical Design

Methodology for Application Driven Low Power Protocol Design

• A Low Power MAC Design Based on DMCA and Wakeup Radio

• A Flexible and Clean MAC Interface for Upper Layer to Do Aggressive Tradeoff between Communication and Computation.

• Motivate More Innovations in Radio Architecture for Low Power System

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Q & A

Thanks !