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Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He University of Minnesota, Twin Cities.

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Presentation on theme: "Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He University of Minnesota, Twin Cities."— Presentation transcript:

1 Shuo Guo, Song Min Kim, Ting Zhu, Yu Gu, and Tian He University of Minnesota, Twin Cities

2 Target Tracking Border Control Environmental Monitoring Habit Monitoring Precision Agriculture Infrastructure Integrity Analysis Inventory Control Traffic Control Assisted Living Interactive Gaming Space Monitor  For hostile environment  For unattended operations  For low deployment & maintenance cost 2

3  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 State Dormant State … Receiver t

4  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! Active State Dormant State B C D A B C D A t B CD 3 Transmissions in total!

5  What if working schedules can be flexibly changed? Active State Dormant State B C D A B C D A t B CD 3 Transmissions in total!

6  What if working schedules can be flexibly changed? Active State Dormant State B C D A B C D A t B+C+D 1 Transmissions in total!

7  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

8  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 S S S R1R1 S R2R2 S RNRN … ACK Collision!

9 LLet highly correlated nodes to wake up at the same time and receive flooding packets simultaneously ◦A◦A flooding tree is built with the consideration of both link quality and link correlation F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!

10  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% ?

11  Experiment: 1 sender, 40 receivers, 100 packets  Receivers record the reception status using a bitmap 11 S S S R1R1 1110111111 S R2R2 90% 80%1100111111 S R 40 … 110111110070% Pr(R 1 |R 2 ) = 100% Pr(R 2 |R 40 ) = 86% Pr(R 1 |R 2 R 40 ) = 100% Link QualityLink Correlation?

12  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

13  Two-node case:  N-node case: 13 With correlated links, q 12 ↑, E(m) ↓ ↓ with correlation, E(m) ↓

14  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

15  Group Division: nodes with higher correlation are divided into the same group, using k- mean 15

16  Sender Selection: nodes selects its flooding parent to make the worst link in each group as high as possible 16 S R3R3 S R1R1 S R2R2 S S1S1 S S2S2 80% 85% 95% 70% w/o link correlation: R 1 chooses S 2 w/ link correlation: R 1 chooses S 1

17  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

18  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

19 Group # Flooding Delay Group # Flooding Coverage Flooding DelaysFlooding Coverage Ratios

20 Group # Data Packets Sent Group # ACKs Sent 50% 10% Energy Cost on Data PacketsEnergy Cost on ACKs

21 21 Data Packets Sent Network Size ACKs Sent Energy Cost on Data PacketsEnergy Cost on ACKs 70% 25%

22  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)

23  THE END

24  A test-bed experiment with 1 sender and 40 receivers  Sender broadcasts 100 packets while receivers recording the reception results 111110111111…11100010 Length=100

25  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? A: 11011------80% link quality B: 11011------80% link quality Correlation: Pr(A|B) = 100% !

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