(slides) a decentralized method for maximizing k-coverage lifetime in wsns
DESCRIPTION
Katsuma, R., Murata, Y., Shibata, N., Yasumoto, K., Ito, M.: "A Decentralized Method for Maximizing k-coverage Lifetime in WSNs," Proc. of The Sixth International Conference on Mobile Computing and Ubiquitous Networking (ICMU 2012), pp.16-23, May.23, 2012. http://ito-lab.naist.jp/mediawiki/images/1/17/Icmu2012.pdf In this paper, we propose a decentralized method for maximizing lifetime of data collection wireless sensor networks (WSNs) by making minimal number of nodes operate and putting other nodes in sleep. We divide a target field into multiple grids and make nodes in each grid locally achieve k-coverage. We can reduce energy consumption of WSN by minimizing the number of active nodes required for kcoverage. However, coverage degree is likely to go to excess beyond k near border between grids when deciding active nodes in each grid independently. To solve this problem, our method decides the minimal set of active nodes for adjoined grids at different times so that k-coverage of a grid is achieved taking into account the coverage in its neighboring grids. Through computer simulations, we confirmed that the proposed method achieved distribution of WSN processing with a small decrease of k-coverage lifetime compared to the centralized algorithm.TRANSCRIPT
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A Decentralized Method for Maximizingk-coverage Lifetime in WSNs
Ryo Katsuma*, Yoshihiro Murata**, Naoki Shibata†,
Keiichi Yasumoto‡, Minoru Ito‡
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* Osaka Prefecture University, ** Hiroshima City University, † Shiga University, ‡ Nara Institute of Science and Technology
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Overview of Our Study Goal
To maximize lifetime of wireless sensor networks (WSNs)
Approach Sleep scheduling for each node by decentralized algorithm
Divide the field into grids and choose leader node for each grid Periodically make each leader node calculate the minimal set of
active nodes in its grid Periodically change the leader for each grid
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Outline
1. Outline of our study
2. Research background
3. Related work
4. Proposed method
5. Evaluation
6. Conclusion
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Target WSNs WSNs for Data Collection
Many small sensor nodes are deployed in the field Sensor nodes periodically sense environmental
information Nodes send data to sink node by multi-hop
communication
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sink
Target field
20℃21℃ 21℃
18℃22℃20℃
23℃
21℃
21℃
20℃ MICA mote
Example of sensor node
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Two Big Problems Problem to maximize lifetime
WSNs are expected to operate for a long time Sleep scheduling for each node is required
Activating minimum number of nodes required for WSN operation
Other nodes sleep in order to save energy
Nodes are activated in turn
k-coverage problem A sensor node covers a circular area for sensing k-covering the entire field by active sensors
Any point in the field is covered by at least k sensors Adjust k to monitor the area with required accuracy
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2-covered
Sensor node
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Challenge
Maximizing k-coverage lifetime Lifetime is the time while the entire field is k-
covered
Battery energy is consumed in each node optimal set of active nodes changes
According to remaining battery energy
We need periodical reclculation
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Outline
1. Outline of our study
2. Research background
3. Related work
4. Proposed method
5. Evaluation
6. Conclusion
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Our Previous Work (1/3)
Sleep scheduling method Sufficient number of nodes are deployed Deciding minimal set of active nodes for k-covering
the field When battery is exhausted for some node Recalculate a set of active nodes
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sink
batteryexhauste
d
activate
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field
Our Previous Work (2/3) Sequential activation algorithm
For deciding minimal set of active nodes Activate a node with the largest contribution area
one after another until the field is k-covered Contribution area
The area newly covered when the node is activatede.g. If A is active, contribution area of D is larger than C
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A
B
C
D
ED Active node
CA
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Our Previous Work (3/3) Centralized calculation by sink node
Collects sensor node information Remaining energy Position
Calculates the minimal set of active nodes Sends the result to every node
WSNs with a large number of nodes Long calculation time High overhead for sending result
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We propose a decentralized method
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Outline
1. Outline of our study
2. Research background
3. Related work
4. Proposed method
5. Evaluation
6. Conclusion
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Assumptions Deployed nodes
Enough number of sensor nodes for k-coverage Only one sink node
Sensor nodes Limited battery energy Sensing range radius is rs
Maximum communicable range radius is rc ( rs < rc )
Sensor node can save battery by sleeping and waking up by timer
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rs
rc
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Initial Configuration Dividing field into grids
k-covering entire field by k-covering each grid Side length of grid should be shorter than
To guarantee that a node can communicate every node in the surrounding 8 grids
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rc
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Leader Node Selection Selecting leader node for each grid
Calculate minimal set of active nodes for k-covering its grid by sequential activation algorithm
Collect all sensing data in its grid and send to sink
Periodically selects the node with highest remaining battery as the leader node A set of active nodes is calculated after the leader node
is selected
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Excessive Coverage Problem If active nodes are independently selected in each grid
Number of coverage exceeds k near the grid border
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A
B
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Grid Ci Grid Cj
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Excessive Coverage Problem If active nodes are independently selected in each grid
Number of coverage exceeds k near the grid border
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A
B
C
D
E
F
G
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Grid Ci Grid Cj
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Excessive Coverage Problem If active nodes are independently selected in each grid
Number of coverage exceeds k near the grid border
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A
B
C
D
E
F
G
H
I
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Grid Ci Grid Cj
Excessively covered
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Our Idea Deciding the minimal set of active nodes for adjoined
grids in multiple steps Considering the area already covered by the nodes in the
adjoined grids
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A
C
D
F
G
I
Grid Ci Grid Cj
A. We need only 2 steps
P
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HB E
Coverage informationQ. How many steps do we need to complete the entire calculation?
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Bi-coloring Classifying all grids into two
groups White and black, like a checkerboard Any two adjoining grids have different
colors Active nodes are chosen in white grids
Computation in black grids is performed after computation in neighboring white grids
Prevent excessive coverage Complete computation in 2 steps
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① ①
① ① ①
① ① ①
① ①
① ①
② ②
② ② ②
② ②
② ② ②
② ② ②
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Data Collection Each sensor node sends sensed data to leader node Leader nodes send the data to the sink
Constructing DAG Connecting other leader nodes that are closer to the sink
Sending data to the node with the largest remaining energy
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sink
Leader node
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Outline
1. Outline of our study
2. Research background
3. Related work
4. Proposed method
5. Evaluation
6. Conclusion
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Simulation Evaluate k-coverage lifetime by the proposed method Compared proposed method with centralized method
WSN parameters Field size: 50[m] × 50[m] Number of nodes: 600 - 1000, random deployment Requested coverage: k = 1 and 3 Sensing frequency: 0.1[Hz] Recalculation interval: 1000[s]
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Result k-coverage lifetime
Proposed method is only 14% less than centralized method Calculation time (1000 nodes)
Proposed method: 0.1 second, centralized method: 1.2 second
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Conclusion Target problem
Maximizing k-coverage lifetime by sleep scheduling Proposed method
Dividing the field into two-colored grids like a checkerboard
Deciding the minimal set of active nodes taking into account the coverage already decided by neighbor grids
Simulation result k-coverage lifetime is only 14% less than centralized
method Shorter computation time
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