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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
Yu Gu@SenSys’07
Sensor States Representation
Scheduling Bits(10110101)*
Switching Rate0.5HZ 16s round time On
10110101
Off
Yu Gu@SenSys’07
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
Yu Gu@SenSys’07
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
Yu Gu@SenSys’07
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
Yu Gu@SenSys’07
Testbed Results
20 MicaZ nodes, 27,398 bytes code memory and 1,137 bytes data memory
Yu Gu@SenSys’07
Simulation Results (1)DSF
Yu Gu@SenSys’07
Simulation Results (2)
DSF
DSF converges to DESS at perfect link
Yu Gu@SenSys’07
Simulation Results (3)
DSF and ETX
Yu Gu@SenSys’07
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