Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He University of Minnesota, Twin Cities.
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Transcript of Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He University of Minnesota, Twin Cities.
Correlated Flooding in Low-Duty-Cycle Wireless
Sensor Networks
Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He
University of Minnesota, Twin Cities
The Need for Long-Term Operation
TargetTracking
BorderControl
EnvironmentalMonitoring
HabitMonitoring
PrecisionAgriculture
InfrastructureIntegrity Analysis
InventoryControl
TrafficControl
AssistedLiving
InteractiveGaming
SpaceMonitor
For hostile environment For unattended operations For low deployment &
maintenance cost
2
How to Prolong WSNs’ Lifetime? Most effective solution: Low-Duty-Cycle
WSN◦ Sensor nodes stay active for a very short interval
and then turn off almost everything and go to sleep
◦ A node periodically switches between active state and dormant state
3
t
…Sender
Active StateDormant State
…Receivert
State-of-arts uses unicasts to do broadcasting/flooding◦ Lai et al., DCOSS’10, Sun et al., Sensys’09, Guo et al.,
MobiCom’09, Inefficient use of energy!
Existing Solutions
Active StateDormant State
B
CD
A
BCD
At
B C D
3 Transmissions in total!
What if working schedules can be flexibly changed?
Existing Solutions
Active StateDormant State
B
CD
A
BCD
At
B C D
3 Transmissions in total!
What if working schedules can be flexibly changed?
Existing Solutions
Active StateDormant State
B
CD
A
BCD
At
B+C+D
1 Transmissions in total!
Build an energy-efficient flooding tree as the basic flooding structure
Children of a common parent tune their working schedules to wake up simultaneously
Children send ACKs to acknowledge the reception
Basic Idea
How to build an energy-efficient flooding tree?◦ Traditional way that only considers link quality is
not sufficient How to avoid ACK-implosion problem?
◦ Should reduce ACKs sent back by the receivers, but still guarantee reliability
New Challenges
S
S
S
R1
S
R2
S
RN
…
ACK ACK ACK
Collision!
Idea of Correlated Flooding Let highly correlated nodes to wake up at
the same time and receive flooding packets simultaneously ◦ A flooding tree is built with the consideration of
both link quality and link correlation For the same sender, ACK is only sent by
the node with the lowest link quality, to eliminate the ACK implosion problem.
9
More Energy Efficient!
Eliminate ACK-Implosion!
Link Correlation Link Correlation is the phenomenon that the
reception results of a broadcasting packets at different nodes are not independent
10
Given that a broadcasting packet is successfully received by B, what is the probability that it is also received by A?
=95%: no correlation!>95%: positive correlation!< 95%: negative correlation!
Pr(A|B) Pr(A) = 95%
?
Existence of Link Correlation Experiment: 1 sender, 40 receivers, 100
packets Receivers record the reception status using a
bitmap
11
SS
SR1 1110111111
SR2
90%
80%1100111111
SR40
…
1101111100 70%
Pr(R1|R2) = 100%
Pr(R2|R40) = 86%
Pr(R1|R2R40) = 100%
Link Quality Link Correlation?
Existence of Link Correlation Experiment: 1 sender, 40 receivers, 100 packets Blue: distribution of link quality, # of packets
received Red: distribution of # of packets received, given the
successful reception at other links with lower link quality
12
Impact of Link Correlation on Flooding
Two-node case:
N-node case:
13
With correlated links, q12 ↑, E(m) ↓
↓ with correlation, E(m) ↓
Construction of Flooding Tree Group Division
◦ Senders divide their receivers into a number of groups with high correlation within the group
Sender Selection◦ Each receiver selects only one sender to optimize
the overall performance
14
Construction of Flooding Tree Group Division: nodes with higher
correlation are divided into the same group, using k-mean
15
Construction of Flooding Tree Sender Selection: nodes selects its flooding
parent to make the worst link in each group as high as possible
16
SR3 SR1 SR2
SS1 SS2
80%85% 95%70%
w/o link correlation:R1 chooses S2
w/ link correlation:R1 chooses S1
Idea of Correlated Flooding Let highly correlated nodes to wake up at
the same time and receive flooding packets simultaneously ◦ A flooding tree is built with the consideration of
both link quality and link correlation For the same sender, ACK is only sent by
the node with the lowest link quality, to eliminate the ACK implosion problem.
17
Evaluation Test-bed implementation
◦ 20 MicaZ nodes form a 2-hop network Simulation Setup
◦ Randomly generated network, 200~1000 nodes Baseline
◦ Traditional Energy-Optimal Tree
18
Test-bed Results
Group #
Flood
ing
Dela
y
Group #
Flood
ing
Covera
ge
Flooding Delays Flooding Coverage Ratios
Test-bed Results
Group #
Data
Pack
ets
Sen
t
Group #
AC
Ks
Sen
t
50%10
%
Energy Cost on Data Packets Energy Cost on ACKs
Simulation Results
21
Data
Pack
ets
Sen
t
Network Size Network Size
AC
Ks
Sen
t
Energy Cost on Data Packets Energy Cost on ACKs
70%
25%
Experimentally verify the existence of link correlation, followed by a theoretical study about its impact on broadcasting/flooding
Utilizes the information of both link quality and link correlation to build an energy efficient flooding tree that saves the energy cost on data packets
Receptions at highly correlated nodes are Acknowledged by only one ACK, saving the energy cost on control packets (ACKs)
Summary of Contributions
THE END
A test-bed experiment with 1 sender and 40 receivers
Sender broadcasts 100 packets while receivers recording the reception results
Existence of Link Correlation
111110111111…11100010
Length=100
Link quality: how many 1s are there in a single bitmap?
Link correlation: how many 1s are there in node A’s bitmap while the corresponding bit in node B’s bitmap is 1?
Existence of Link Correlation
A: 11011------80% link qualityB: 11011------80% link qualityCorrelation: Pr(A|B) = 100% !
Existence of Link Correlation
Existence of Link Correlation