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Design and Evaluation of a Versatile and Efficient Receiver-Initiated Link Layer for Low-Power Wireless

Prabal Dutta, Stephen Dawson-Haggerty, Yin Chen,Chieh-Jan (Mike) Liang, and Andreas Terzis

Sensys 2010

Presenter: SY

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OutlineIntroductionA-MAC primitiveImplementationBackcast evaluationHigh level evaluationDrawbacksConclusion

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A sender-initiated MAC:Sender triggers communications by transmitting a data

Receiver

Sender Listen D

DListen

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Low-power listening (LPL) with a sender-initiated MAC

Preamble DSender

Receiver D

Tlisten Noise

Overhearing/noise adds significant unpredictability to node lifetime

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A receiver-initiated MAC:Receiver triggers exchange by transmitting a probe

Receiver

Sender PListen D

P D

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Receiver-initiated services -- benefitsHandle hidden terminals better than sender-initiated

ones

Support asynchronous communication w/o long-preambles

Support extremely low duty cycles or high data rates

Support many low-power services Wakeup (“LPP”, Musaloiu-E. et al., IPSN’08) Discovery (“Disco”, Dutta et al., Sensys’08) Unicast (“RI-MAC”, Sun et al., Sensys’08) Broadcast (“ADB”, Sun et al., Sensys’09) Pollcast (“Pollcast”, Demirbas et al., INFOCOM’08) Anycast (“Backcast”, Dutta et al., HotNets’08)

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Receiver-initiated services -- drawbacksProbe (LPP) is more expensive than channel sample (LPL)

Baseline power is higher

Frequent probe transmissionsCould congest channel & increase latencyCould disrupt ongoing communicationsChannel usage scales with node density rather than

traffic

Services use incompatible probe semanticsMakes concurrent use of services difficultSupporting multiple, incompatible probes increases

power

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The probe incompatibility mess

Probes use hardware acknowledgementsProbes do not use hardware acknowledgementsProbes include only receiver-specific dataProbes include sender-specific data tooProbes include contention windowsProbes do not include contention windows

Pollcast

RI-MACLPP

Backcast

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Is it possible to design a general-purpose,

yet efficient, receiver-initiated link layer?

9

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Most consequential decision a low-power MAC makes:stay awake or go to sleep?

Preamble DTX

RX D

Tlisten Noise

TX

RX

P

P

DATA

DATA

Listen

Sender-Initiated: Channel Sampling

Receiver-Initiated: Channel Probing

P10

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Solving the synchronization problem with BackcastA link-layer frame exchange in which:

A single radio PROBE frame transmission Triggers zero or more identical ACK frames Transmitted with tight timing tolerance So there is minimum inter-symbol interference And ACKs collide non-destructively at the receiver

P ATX

RX P A

P ATXYou sh

ould be skeptica

l that th

is idea might

work

P. Dutta, R. Musaloiu-E., I. Stoica, A. Terzis, “Wireless ACK Collisions Not Considered Harmful”,HotNets-VII, October, 2008, Alberta, BC, Canada

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OutlineIntroductionA-MAC primitiveImplementationBackcast evaluationHigh level evaluationDrawbacksConclusion

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A-MAC: An 802.15.4 receiver-initiated link layer

P ASender

Receiver P A

DATA

DATA

Max data packet

4.256 ms

ACK transmission time 352 µs

RXTX turnaround time: 192 µs

P

P

Listen

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A-MAC’s contention mechanism

Receiver

Sender

Sender P AListen D P-CW

P AListen D P-CW

P A D P-CW D

BO

D

frame collisionBackcast

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A-MAC’s parallel multichannel data transfersuse control, data (1), and data (2) channels

P ASender 1

Receiver 1 P A

DATA

DATA

P

P

Listen

P ASender 2

Receiver 2 P A

DATA

DATA

P

P

Listen

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OutlineIntroductionA-MAC primitiveImplementation

UnicastBroadcastPollcastWakeup

Backcast evaluationHigh layer evaluationConclusion

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Unicast

P ANode 2(Receiver)

Node 3(Sender)

P ANode 1(Sender) Listen

DDST=0x8002SRC=0x0002

D P

P L

MAC=0x8002

P AListen D P-CWMAC=0x8002

P AListen D P-CWMAC=0x8002

P A D P-CW D

BO

D

DST=0x8002SRC=0x0002ACK=0x0023FRM=0x0001

DST=0x0002SRC=0x0001SEQ=0x23

frame collisionBackcast

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Broadcast

TX 1

RX 2

RX 3

RX 4

Listen P A Listen P A Listen

P A

P A

Backcast

auto-ack=onaddr-recog=off

D

D

P

P

D

D

P

P

P A D P

P A D P

DST=0x8002SRC=0x0002

DST=0x8002SRC=0x0002ACK=0x0023FRM=0x0001

DST=0x0002SRC=0x0001SEQ=0x23

offoff

onoff

BackcastBackcast

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Wakeup

P ANode 2

Node 3

Node 4

P ANode 1

Node 5

Listen

Listen P A Listen P A Listen

P A Listen

Listen

P A

P A

Listen P A

P

P

A

A

Backcast

DST=0xFFFFSRC=0x0002

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Pollcast

Node 2(Receiver)

Node 3(Sender)

Node 1(Sender) PredEvent

PredEvent

Pred

M. Demirbas, O. Soysal, and M. Hussain,“A Single-Hop Collaborative Feedback Primitive for Wireless Sensor Networks”,INFOCOM’08, April , 2008, Phoenix, AZ

ListenMAC=0x8765

ListenMAC=0x8765

Listen

P A

P A

P A

Backcast

DST=0xFFFFSRC=0x0002

PRED=elephantMAC=0x8765

EventDST=0x8765

P+Pred

P+Pred

P+PredDST=0xFFFFSRC=0x0002

PRED=elephant

A

A

A

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OutlineIntroductionA-MAC primitiveImplementationBackcast evaluationHigh level evaluationDrawbacksConclusion

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Evaluating Backcast: equal-power, equal-path delaySetup Methodology

Platform: Telos moteProtocol: IEEE 802.15.4Radio: Texas Instruments

CC2420Experiment

8 responder nodes Connect w/ splitter/attenuator Turned on sequentially Transmit 100 packets 125 ms inter-packet interval Log

RSSI: received signal strength LQI: chip correlation rate ARR: ACK reception rate

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As the number of colliding ACKsgoes from one to eight…

But, for two nodes, LQI exhibits outliers and a lower median

Median RSSI increaseslogarithmically

Median LQI remains nearly constant but is more left-tailedACK reception rate stays practically constant

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Backcast scales to a large number of nodes

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Energy cost of A-MAC primitives:probe, receive, transmit, and listen

25

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Idle listening cost: under heavy interference

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OutlineIntroductionA-MAC primitiveImplementationBackcast evaluationHigh level evaluationDrawbacksConclusion

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A-MAC offers modest unicast performance

28

R

S SS S

Collision Domain

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A-MAC supports multiple parallel unicast flows

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RS

RS

RS

CollisionDomain

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A-MAC wakes up the network fasterand more efficiently than LPL (Flash) flooding

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Faster Wakeup

Fewer Packets

A-MAC

LPL (Flash)

A-MACLPL (Flash)

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A-MAC wakeup works well at low duty cycles

31“Wakeup Latency” is

normalized to the probe interval

Tprobe = 4,000 ms

Pavg = 63 µWIavg = 21 µA

N = 59

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Supporting the Collection Tree Protocol (CTP),A-MAC beats LPL on nearly every figure of merit

32

R

S

S

SS

SS

S SN = 59Tdata = 60 sTprobe = 500 ms

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The effect of interference on idle listening:Sampling, Probing, and Backcast

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Sampling

Channel 18 Channel 26

ProbingBackcast

Sampling

Probing

Backcast

Background noise/traffic/noise in an office environment

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OutlineIntroductionA-MAC primitiveImplementationBackcast evaluationHigh level evaluationDrawbacksConclusion

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35

Primitive

P ASender

Receiver P A

DATA

DATA

Max data packet

4.256 ms

ACK transmission time 352 µs

RXTX turnaround time: 192 µs

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Backcast degrades when path delay differences exceeds approximately 500 ns (500 ft free space)

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A-MAC single channel PDR degrades with high node density and high probe frequency

37

S

RS

S

CollisionDomain

S S

S S S S

S

SSSS

S S

S S

S

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ConclusionBackcast provides a new synchronization primitive

Can be implemented using a DATA/ACK frame exchange Works even with a 8, 12, 94 colliding ACK frames Faster, more efficient, and more robust than LPL, LPP

A-MAC augments Backcast to implement Unicast Broadcast Network wakeup Robust pollcast

Results show Higher packet delivery ratios Lower duty cycles Better throughput (and min/max fairness) Faster network wakeup Higher channel efficiency