1. The Coverage Problem in a Wireless Sensor Network
Author : chi-Fu Huang, Yu-Chee Tseng
Presenter : Young-Hwan Kim

2. Contents Introduction Problem statement The proposed solutions
Applications and extensions of the coverage problem
Conclusion
2008 ICL seminar

3. Introduction Definition Features
Network of sensor nodes with computation, sensing, wireless communication capabilities
Features
Embedded computer with sensors and radios
Sensing target in proximity
Large number of densely distributed nodes
Multi-hop, wireless, ad hoc network
Sensing, processing, communication, actuation 3
2008 ICL seminar

4. Introduction Issue Consideration of design
Coverage Problem (&Connectivity)
Coverage and Schedule
Localization and Location Estimation
Identifying Set Problems
Consideration of design
Energy constraint
Relation of whole network system
whole network life time
Prior to global(whole) goal than individual requirements 4
2008 ICL seminar

5. Problem statement Assumption
Set of sensors, S = {s1, s2, …, sn}, in a two-dimensional area A
Each sensor is located at (xi, yi) inside A
Each sensor has a sensing range of ri 5
2008 ICL seminar

6. Problem statement Two versions of the coverage problem – k-NC
The sensing ranges
are non-unit disks 6
2008 ICL seminar

7. Problem statement Two versions of the coverage problem – k-UC
The sensing ranges
are unit disks 7
2008 ICL seminar

8. Naive solution
Find out all sub-regions divided by the sensing regions of all n sensors
Check if each sub-region is k-covered or not
Complexity – O(n^2) : because of many sub-regions
Difficult to calculate sub-regions 8
2008 ICL seminar

9. K-UC Problem (proposed solution)
Complexity – O(ndlogd) : polynomial-time algorithm
n : the number of all sensors in whole network area
d : the maximum number of sensors that may intersect a sensor
Look at how the perimeter of each sensor’s sensing range is covered
By collecting k-perimeter-coverage information from all sensors, a correct decision can be made
2008 ICL seminar

10. K-UC Problem Calculation 2008 ICL seminar Two sensor : location :
distance
angle
condition 10
2008 ICL seminar

11. K-UC Problem
Processing 11
2008 ICL seminar

12. K-UC Problem 12
2008 ICL seminar

13. K-UC Problem
Exception-1 13
2008 ICL seminar

14. K-UC Problem
Exception-2 14
2008 ICL seminar

15. K-NC Problem
Case1: 15
2008 ICL seminar

16. K-NC Problem
Case1: 16
2008 ICL seminar

17. K-NC Problem
Case1: 17
2008 ICL seminar

18. K-NC Problem
Case2: 18
2008 ICL seminar

19. K-NC Problem
Case2: 19
2008 ICL seminar

20. K-NC Problem
Case2: 20
2008 ICL seminar

21. Discovering Insufficiently Covered Regions
A larger k can support a more fine-grained sensibility
Processing
Central controller(FFD) broadcast the desired value of k
Each sensor communicate with its neighboring sensors
Calculate and compare k
Results are sent back to the central controller
Problem
How can we patch insufficiently covered areas
Granularity versus cost ( trade-off relation ) 21
2008 ICL seminar

22. Power Saving in Sensor Networks
Turn off redundant nodes to save energy
Processing
Assumption
Candidates is nodes who can be turned off
Candidate if all its neighbors are still k-perimeter-covered after si is removed 22
2008 ICL seminar

23. Hot Spots Definition Solution
More important than other areas( need to more sensors )
Solution
To check whether a hot spot area is k-covered or not 23
2008 ICL seminar

24. Extension to Irregular Sensing Regions
Cause
Sensing region of a sensor is not necessarily a circle
Solution
Through Lemma 1 and theorem 1, translate perimeter-covered property of sensors 24
2008 ICL seminar

25. Extension to Irregular Sensing Regions
How to determine the perimeter coverage
-> use polygon approximation 25
2008 ICL seminar

26. Conclusion Proposed solutions solve coverage problem
Decision problem : sensing area is sufficiently covered or not
Base on checking the perimeter of each sensor’s sensing range
Scheme give exact answer in O(ndlogd) time
Discuss several applications and extensions 26
2008 ICL seminar