Yu Gu and Tian He

Minnesota Embedded Sensor System (MESS)Department of Computer Science & Engineering

http://mess.cs.umn.edu

This work is supported by National Science Foundation

Sleep Latency in Low Duty-Cycle Sensor Networks

Sleep now. Wake up in 35 seconds

Sleep now. Wake up in 4 seconds

Sleep now. Wake up in 57seconds

Sleep now. Wake up in 13 seconds

35s latency

57s latency

4s latency13s latency

A

B

C

D

E

Yu Gu@SenSys’07

Unreliable Radio Links

90%

95%

50%

70%

A

B

C

D

E

Yu Gu@SenSys’07

State-of-the-art Solutions: ETX (MobiCom’03)

50%, 100s

50%, 100s

40%, 10s40%, 10s

ETX = 1/0.5 + 1/0.5 = 4

ETX = 1/0.4 + 1/0.4 = 5

Expected E2E delay is 400s

Expected E2E delay is 50s

A

B

C

D

Sole link quality based solutions cannot help reduce E2E delay in extremely low-duty cycle sensor networks!

ETX only considers link quality

Yu Gu@SenSys’07

State-of-the-art Solutions: DESS (INFOCOM’05)

10%, 10s10%, 10s

100%, 20s

100%, 20s

DESS = 10 + 10 = 20s

DESS = 20 + 20 = 40s

Expected E2E delay is 200s

Expected E2E delay is 40s

A

B

C

DSole sleep latency based solutions cannot help reduce E2E delay in extremely low-duty cycle sensor networks!

DESS only considers sleep latency

Yu Gu@SenSys’07

State-of-the-art Solutions (2)

Only Consider impact of link qualities

Only Consider impact of Duty Cycling

80 fold performance degradation!

20 fold performance degradation!

Intelligent MAC protocols (B-MAC, S-MAC, SCP-MAC …) provide significant performance improvement at the MAC layer.We focus on further performance improvement at the network layer.

Yu Gu@SenSys’07

OutlineMotivationMotivationNetwork ModelDSF DesignEvaluationConclusion

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Sensor States Representation

Scheduling Bits(10110101)*

Switching Rate0.5HZ 16s round time On

10110101

Off

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Data Delivery Process

1 2 3 4

Sleep latency is 1

Sleep latency is 2

Sleep latency is 3

E2E Delay is 6

(1000000000)* (0100000000)* (0001000000)* (0000001000)*

Yu Gu@SenSys’07

1st attempt: Sleep latency is 1

Main Idea

1 2 3 4

(1000000000)* (0100000000)* (0001000000)* (0000001000)*

Sleep latency is 1

2nd attempt: Sleep latency is 1 + 10 =11ith attempt: Sleep latency is 1 + 10 * (i-1)

(0010000000)*

5

2nd attempt: Sleep latency is 1 + 1 =2

We should try a sequence of forwarding nodes instead of a fixed forwarding node!

Dynamic Switching-based Forwarding (DSF) is important in extremely low duty-cycle sensor networks.

Yu Gu@SenSys’07

Optimization ObjectivesEDR: Expected Delivery Ratio

EED: Expected End-to-End Delay

EEC: Expected Energy Consumption

AssistedLiving

TargetTracking

BorderControl

DisasterResponse

HabitMonitoring

EnvironmentalMonitoring

SpaceMonitor

TrafficControl

PrecisionAgriculture

Yu Gu@SenSys’07

Optimization Objectives(1) : EDR

1 3

4

(100)*

(100)*EDR = 90%

(001)*EDR = 80%

(010)*EDR = 70%

260%

50%

40%

EDR: Expected Delivery Ratio.

0.6*0.7

+ (1-0.6)*0.5*0.8

+ (1-0.6)*(1-0.5)*0.4*0.9

EDR for node 1 is (EDR1):

Forwarding Sequence

Yu Gu@SenSys’07

Optimization Objectives(2) EDR: Expected Delivery Ratio

EED: Expected End-to-End Delay

EEC: Expected Energy Consumption

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Optimizing EDR

1

3

(100)*

(001)*EDR = 80%

2 (010)*EDR = 70%

100%

100% If only node 3 is selected as forwarding node:

EDR1 = 1 * 0.8 = 0.8

We should only choose a subset of neighboring nodes as forwarding nodes!

Shall we try all available neighbors?

If both node 2 and node 3 are selected as forwarding nodes:

EDR1 = 1 * 0.7 = 0.7

Yu Gu@SenSys’07

Optimizing EDR with dynamic programming

1

2

3

4

(100)*

(100)*EDR = 90%

(001)*EDR = 80%

(010)*EDR = 70%

60%

50%

40%

Select only a subset of neighbors as forwarders

Node 4 has to be selected

Then we attempt to add more nodes into the forwarding sequence backwardly.

Try or skip

Try or skip

Try or drop

Yu Gu@SenSys’07

Distributed Implementation

sink

42

1 3

EDR = 98%, EED = 2, EEC = 1

EDR = 99%, EED = 15, EEC = 2

EDR = 100%, EED = 0, EEC = 0

EDR = 97%, EED = 20, EEC = 5

EDR = 90%, EED = 90, EEC = 12

Yu Gu@SenSys’07

Interesting FindingsTemporary routing loops may be helpful on

reducing E2E Delay

1

3

5

4

2

(111111)*

(111111)*

(010000)*

(111111)*

(000010)*

(100%,1)

(90%,1)

(90%,1)

(100%,1)

(100%,1)

Yu Gu@SenSys’07

OutlineMotivationMotivationNetwork ModelNetwork ModelDSF DesignDSF DesignEvaluationConclusion

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EvaluationsBoth testbed implementation and large-scale

simulations

Baseline solutions:ETX by Douglas S.J. De Couto et al. in

Mobicom’03PRR*D by Karim Seada et al. in SenSys’04DESS by Gang Lu et al. in INFOCOM’05

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Testbed Results

20 MicaZ nodes, 27,398 bytes code memory and 1,137 bytes data memory

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Simulation Results (1)DSF

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Simulation Results (2)

DSF

DSF converges to DESS at perfect link

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Simulation Results (3)

DSF and ETX

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ConclusionA Dynamic Switch-based Forwarding (DSF) scheme

for extremely low duty-cycle sensor networksAddressed both sleep latency and lossy radio linksDynamic switching is essential

Distributed model for data delivery ratio (EDR), E2E delay (EED) and energy consumption (EEC).Optimal forwarding on these three metricsA generic metrics that converge to ETX (in always-

awake networks) and DESS (in perfect-link networks)

Yu Gu@SenSys’07