network and systems laboratory nslab.ee.ntu.edu.tw prabal dutta, stephen dawson-haggerty, yin chen,...
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Network and Systems Laboratorynslab.ee.ntu.edu.tw
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
Network and Systems Laboratorynslab.ee.ntu.edu.tw
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
P
10
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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
RXP A
P ATX
You sh
ould b
e skeptic
al that t
his id
ea mig
ht
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 collision
Backcast
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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-CW
MAC=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 collision
Backcast
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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
Backcast
Backcast
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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
Listen
MAC=0x8765
Listen
MAC=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
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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
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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
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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
Probing
Backcast
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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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
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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