improving the coverage of randomized scheduling in wireless sensor networks
DESCRIPTION
Improving the Coverage of Randomized Scheduling in Wireless Sensor Networks. 林振緯 [email protected]. Department of Computer Science and Information Engineering Fu Jen Catholic University. Outline. Introduction Background Proposed Approach Simulation Evaluations Conclusions. - PowerPoint PPT PresentationTRANSCRIPT
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Improving the Coverage of Randomized Scheduling in Wireless Sensor Networks
Department of Computer Science and Information EngineeringFu Jen Catholic University
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Outline
IntroductionBackgroundProposed ApproachSimulation EvaluationsConclusions
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Wireless Sensor Network (WSN) Applications軍事應用
– 監控戰場上的狀態環境應用
– 監測污染或災害防治健康應用
– 偵測人體健康數據與行為家庭應用
– 將含有起動器 (actuator) 的 sensor network 佈署於家中，可以讓人們在遠方或在家裡經由網際網路作許多家事。
工業應用– 偵測產品線上的不良品
Introduction
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An Application Case 用於廠區防災工研院在其光電所晶圓廠務區利用溫度、煙霧感測器偵測工廠環境。當災難發生時，後端伺服器將自動通知管理人員及消防隊，還可透過 WSN逃難指示板引導逃生方向。
Introduction
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Introduction
電力供應單位 (Power Unit)
通常感測節點的電力是由電池所支援，因此在軟硬體的設計上，有效的分配電力是很重要的。
感測單位 (Sensing Unit)負責偵測環境，將感測元件感測到的類比訊號轉換成數位訊號，並將資料送到處理單位加以處理。
傳輸單位(Transceiver Unit)
負責感測元件間的溝通，或是將感測器的資料傳送給無線資料蒐集器。
處理單位 (Processing Unit)Storage ：將蒐集到的環境資訊儲存在儲存元件中Processor ：負責執行事先儲存好的程式碼，以協調並控制感測節點之間不同的單位元件。
應用上：感測器可能包含定位裝置、移動器和能源產生器
Sensor Node Architecture
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Internet, Satellite or other Communication System.
Internet, Satellite or other Communication System.
Introduction
WSN Network Architecture
Sensor Deployment with Random and Redundant Manners
Base station (BS)or
Sink SensorEnvironment
(Field)
Wireless Communicationlink
Sensor node
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coverage holescoverage holescoverage holescoverage holescoverage holescoverage holescoverage holes
A Well-Known Randomized Scheduling for WSN
Introduction
Subset 1
Subset 2
Subset 3
1 2 3 …
Time Slot
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Introduction
MotivationCoverage improvement for the randomized schedulingConnectivity improvement
– Reference C. Liu, K. Wu, Y. Xiao, and B. Sun, “Random Coverage with Guaranteed
Connectivity: Joint Scheduling for Wireless Sensor Networks,” IEEE Trans. Parallel and Distributed Systems, vol. 17, no. 6, pp. 562-575, 2006.
Coverage with connectivity guarantees– No coverage holes– Double range property
Mica1 mote, Mica2 mote, Sensoria SGate, etc.
– Reference G. Xing, X. Wang, Y. Zhang, C. Lu, R. Pless, and C. Gill, “Integrated
Coverage and Connectivity Configuration for Energy Conservation in Sensor Networks,” ACM Trans. Sensor Networks, vol. 1, no. 1, pp. 36-72, 2005.
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Outline
IntroductionBackgroundProposed ApproachSimulation EvaluationsConclusionsReferences
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Background
Network ModelA static sensor network in a two-dimensional field
Circle model used for the sensing and communication ranges
Double range property
Location awareness
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Background
Related WorkRandom Coverage with Guaranteed Connectivity: Joint
Scheduling for Wireless Sensor Networks,” IEEE Trans. Parallel and Distributed Systems
Connectivity guaranteedA given coverage requirement to determine the number of
subsets
e
qln(1 – t)
n1 - k ≤
r : the size of sensing area of each sensor
a : thee size of the whole field
n : the total number of deployed sensor nodes
t : at least network coverage intensity
q = r / a
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Background Related Work
Optimal Geographical Density Control (OGDC) H. Zhang and J. C. Hou, “Maintaining Sensing Coverage
and Connectivity in Large Sensor Networks,” in Journal on Wireless Ad Hoc and Sensor Networks, vol. 1, pp. 89-123, Jan 2005.
Scheduling- Round basis - Coverage and connectivity guarantees- Double range property to guarantee the connectivity - Each round with two phases
node selection and steady state
- Tree states for a sensor node undecided, on , and off
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X
Initially each node is at undecided state
Node A is a starting node
Based on the above step, node Dwill be chosen
• OGDC (Cont.)
Background
undecided state on state off state
A B
C
To cover the crossing point of circle A and B the node whose position is closest to the optimal position X, node C will then be selected. D
E
Because of node E’s neighbors can completely cover its own coverage, so node E turns state to off
One of the neighborswith an (approximate) distance of r (node B)will be selected to be a working node.
3 3 r
r
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Outline
IntroductionBackgroundProposed ApproachSimulation EvaluationsConclusionsReferences
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Proposed Approach
GoalEliminating the blind points (coverage holes) in the
randomized scheduling Improving the coverage quality of the randomized
schedulingBasic idea
Adding extra sensor nodes in each subset- Activating more sensor nodes at each time slot.
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coverage holescoverage holes
extra nodesextra nodesextra nodes
Basic idea (Cont.)
Proposed Approach
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Proposed Approach
ProblemHow to select appropriate sensor nodes as extra sensor nodesHow to minimize the number of extra sensor nodes
Solution A distributed manner based on the four-phase execution
The first phase-Determining the belonging subset of each sensor node (the time slot)
The second phase-Classify the neighbors into two parts for the third phase
The third phase-Calculating the responsible sensing range
The fourth phase-Eliminating the coverage holes in each responsible sensing range
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Proposed Approach
The first phase:Following the randomized scheduling algorithm to
divide the sensor nodes into multiple subsets.Collecting the information about its neighboring
sensor nodes.
The second phase:Using the belonging subset number to classify its
neighbors into two parts:- The neighbors with the same subset.- The neighbors with the different subset.
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Proposed Approach
The neighbors with the same subset
The neighbors with the different subsets
1
3
2
1
1
1
2
2
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3
The second phase (Cont.)
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Proposed Approach
The third phasePartitioning the sensor field using the distribution
manner- Constructing the responsible sensing range
Voronoi polygon
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Proposed Approach
The third phaseConstruing the responsible sensing range (Cont.)
- The number of the neighbors with the same subset is not enough
- Not precisely calculating its responsible sensing region- Introducing the partition-assistant nodes for assisting the
calculation of the responsible sensing region- Additionally work at the time slot of its assisted sensor
node
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No the neighbors with the same subset in the quadrant
Proposed ApproachThe third Phase
Partition-assistant nodes (One kind of the extra sensor nodes)
Asking the farthest neighbor as the partition-assistant node
Sensor node i and neighbors with same subset number
The neighbors without same subset number
The new Voronoi polygon(Its responsible sensing region)
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Proposed Approach
The fourth phase:Determining whether it has the capability to
independently cover its responsible sensing region.Eliminating the coverage holes.
- Introducing the coverage-assistant nodes to collectively cover the responsible sensing region
- Using the optimal circle deployment (circle covering) as the selection template to select the coverage-assistant nodes
- Additionally work at the time slot of its assisted sensor node
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Proposed Approach
The sensing region of sensor node i
The voronoi polygon of sensor node i(its responsible sensing region)
Sensor Node i
Coverage-Assistant Node
Neighbors without the same subset
Ideal sensor node
The third PhaseCoverage-assistant nodes (The other kind of the extra sensor
nodes)
Circle Covering
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Proposed Approach Polynomial Time complexity
The first phase- O( 1 )
The second phase- O( )
The third phase- O( )
The fourth phase
- O( )is
ci HS
R
RV
2
iii VSVSS log
Si : The set of the sensor nodes that are the neighbors of sensor node i and the sensor node i itself.
VSi : The set of the sensor nodes that are the neighbors of sensor node i and have the same working time slot.
Rc : The communication radius of a sensor node.
Rs : The sensing radius of a sensor node.
HSi : The set of sensor nodes that are the neighbors of sensor node i but their working time slots are different
iS
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Outline
IntroductionBackgroundProposed ApproachSimulation EvaluationsConclusionsReferences
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Simulation Evaluations
Simulation SetupSensor field: 200 meters * 200 meters Total number of sensor nodes: 500, 1000, 1500, 2000, and 2500Number of subsets: 2, 3, 4, 5, and 6The communication / sensing radius ratio: 2
Performance MetricsCoverage intensity
- Average ratio of the area covered by a subset over the whole area of the sensor field. Ratio of additional sensor nodes
- Average ratio of the partition-assistant and coverage-assistant nodes in a subset over the total number of sensor nodes
Average number of control messages- How many messages issued for improving the coverage - Energy consumption
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Simulation Results
Coverage Intensity Number of sensor nodes = 1000
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Simulation Results
Coverage Intensity (cont.) Number of subsets = 5
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Ratio of Additional Sensor NodesNumber of sensor nodes = 1000
Simulation Results
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Ratio of Additional Sensor Nodes (Cont.)
Simulation Results
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Simulation Results
Ratio of Additional Sensor Nodes (cont.) / ratio = 2, Number of subset = 5cR sR
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Simulation Results
Average Number of Control Messages
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Outline
IntroductionBackgroundProposed ApproachSimulation EvaluationsConclusions
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Conclusions A distributed approach to improving the coverage
performance of the randomized scheduling algorithm
Partition-assistant and Coverage-Assistant nodes introduced in the subset
Modifying the Voronoi polygon construction and Applying the circle covering
Coverage intensity achieved nearly same as the centralized approach without any subsets
Low energy consumption with the less than 3 control messages issued the polynomial time complexity
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S3
S1
S5S4
S0
S2
Voronoi Diagram
Responsible sensing range
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Circle Covering What is the minimum number of circles required to
completely cover a given polygon? Y. Guo and Z. Qu, “Coverage Control for A Mobile Robot
Patrolling A Dynamic and Uncertain Environment,” Proc. World Congress on Intelligent Control and Automation