You- Chiun Wang, Yung-Fu Chen, and Yu- Chee Tseng

1. Using Rotatable and Directional (R&D) Sensors to Achieve Temporal Coverage of Objects and Its Surveillance Application You-Chiun Wang, Yung-Fu Chen, and Yu-Chee Tseng IEEE TRANSACTIONS ON MOBILE COMPUTING 2011

2. Outline • Introduction • R&D Sensor Surveillance System • Goal • Assumptions • Overview • Maximum Covering Deployment (MCD) Heuristic • Disk-Overlapping Deployment (DOD) Heuristic • Performance evaluation • Conclusions

3. Introduction • Due to hardware design or cost consideration, sensors may possess sector-like sensing coverage . By stepper motors, sensors can rotate to cover the objects around them. • This type of sensors are called rotatable and directional (R&D) sensors. • infrared, camera, and ultrasonic sensors

4. Introduction • R&D sensors have many real-life applications: • providing visual monitoring of the environment • identifying the positions of objects • temporal coverage model • guarantee each object to be monitored by sensors for at least a threshold ratio of time per period.

5. R&D Sensor Surveillance System • The event-driven surveillance system by R&D sensors.

6. Goal • R&D sensor deployment problem • deploy the minimum number of sensors to cover a given set of objects to satisfy their temporal coverage requirements.

7. Assumptions • Static object • Each sensor • sensing range with an opening angle of • sensing radius : rs • omnidirectional communication range radius : rc • same rotation speed • 360o of freedom to rotate counterclockwise • time-Synchronized • have the same frame length that are not necessarily aligned ok a Sector A rs frame frame … Si rs Si 0.5T 0.5T 0.5T 0.5T 0.5T Si the duration that a sensor stops to monitor the objects in one sector A B A B A b the duration that a sensor rotates from one sector to the next sector Sector B

8. Definition during each frame it is monitored by sensors at leastTtime. a Sector A frame frame … Si rs 0.5T 0.5T 0.5T 0.5T 0.5T Si the duration that a sensor stops to monitor the objects in one sector A B A B A b the duration that a sensor rotates from one sector to the next sector Sector B

9. Overview object R&Dsensor Sector C Sector B Sector E Sb Sa Sector G Sector A disk da disk db Sector D Sector F • Maximum Covering Deployment (MCD) Heuristic • Disk-Overlapping Deployment (DOD) Heuristic

10. Maximum Covering Deployment (MCD) Heuristic

11. Maximum Covering Deployment (MCD) Heuristic • MCD suggests deploying sensors on thedisks that cover more objects. • Phase 1: Find a set of disks to cover all objects in . • Phase 2: Iteratively select the disk with the maximum number of unmarked objects, conduct the sector cutting operation to find its sectors, and mark all of its objects. • Phase 3: deploy R&D sensors on the center of that disk and determine its rotation schedule.

12. Maximum Covering Deployment (MCD) Heuristic • Phase 1: Find a set of disks to cover all objects in . [50] B. Xiao, Q. Zhuge, Y. He, Z. Shao, and E.H.M. Sha, “Algorithms for disk covering problems with the most points,” Proc. IASTED Int’l Conf. Parallel and Distributed Computing and Systems, pp. 541– 546, 2003. If two objects have a distance smaller than 2rs, we place two disks such that their circumferences intersect at these two objects. 2) If two objects have a distance equal to 2rs, we place a disk such that its circumference passes these twoobjects. 3)If an object is isolated, in the sense that its distance tothe nearestobject is larger than 2rs, we place a disksuch that its center locates atthe object.

13. Maximum Covering Deployment (MCD) Heuristic • Phase 2: conduct the sector cutting operation to find its sectors, and mark all of its objects. • Indexing and clustering • Deciding sectors Cluster 1 Cluster 1 o3 o3 o2 o2 o4 o4 Sector B o1 o1 o9 o9 o5 o5 Sector A Sa Sa o8 o8 Cluster 3 Cluster 3 Cluster 3 o6 o6 Cluster 2 o7 o7 Cluster 2 Sector C

14. Maximum Covering Deployment (MCD) Heuristic • Phase 2: • Indexing and clustering Cluster 1 Start from this object o1 Sa

15. Maximum Covering Deployment (MCD) Heuristic • Phase 2: • Indexing and clustering Cluster 1 o2 o1 Sa

16. Maximum Covering Deployment (MCD) Heuristic • Phase 2: • Indexing and clustering Cluster 1 o3 o2 o4 o1 o9 o5 Sa o8 Cluster 3 o6 Cluster 2 o7

17. Maximum Covering Deployment (MCD) Heuristic • Phase 2: • Deciding sectors • Cluster sequence : K; 1; 2; ・ ・ ・ ;K − 1. • each cluster starting from the uncovered object with smallest index Cluster 1 Cluster 1 o3 o3 o2 o2 o4 o4 Sector B o1 o1 o9 o9 o5 o5 Sector A Sa Sa o8 o8 Cluster 3 Cluster 3 Cluster 3 o6 o6 Cluster 2 o7 o7 Cluster 2 Sector C

18. Maximum Covering Deployment (MCD) Heuristic • Phase 3:deploy R&D sensors on the center of that disk and determine its rotation schedule. e Sector E a Sector A d rs diskdi diskdj Si f Sector D rs c Sj Sector F b Sector B Sector C

19. Maximum Covering Deployment (MCD) Heuristic • Phase 3:deploy R&D sensors on the center of that disk and determine its rotation schedule. e Sector E a Sector A rs Si f Sector D rs Sj Sector F d diskdi diskdj b Sector B Sector C c

20. Maximum Covering Deployment (MCD) Heuristic • When objects are arbitrarily placed in the sensing field,each sector may cover only few objects. • In this case, eachdisk requires more sectors to cover its objects and thus wemay need to deploy multiple sensors on each of most disks.

21. Disk-Overlapping Deployment (DOD) Heuristic

22. Disk-Overlapping Deployment (DOD) Heuristic • DOD exploits diskoverlap by deploying sensors to cover joint sectors. • Phase 1: Calculatethe set . We then select a subset of disks from to cover all objects in . • Phase2: Find the joint sectors of any two disks in . • Phase3: Calculate the additional disks used to cover the joint sectors. We then deploy R&D sensors on these additional disks and a subset of disks in .

23. Disk-Overlapping Deployment (DOD) Heuristic • Phase 1: Calculatethe set . We then select a subset of disks fromto cover all objects in . • The size of is minimized. • The number of disks with no more than sectors is maximized.

24. Disk-Overlapping Deployment (DOD) Heuristic • Phase 1: • Disk selection scheme • Let = ∅ and set all objects in to unmarked. unmarked object

25. Disk-Overlapping Deployment (DOD) Heuristic • Phase 1: • Disk selection scheme • Sort the disks in by their numbers of unmarkedobjects in a decreasingorder. • select the firstn > 1 disks from • conduct the sector cuttingoperationon each of these n disks independently. • If some disks’sectors, weremove the disks with more than sectors fromthese n disks. • Otherwise, all disks must have more than sectors. In this case, no disks are removed.

26. Disk-Overlapping Deployment (DOD) Heuristic • Phase 1: • Disk selection scheme • Repeat step 2 until all objects in b are marked.

27. Disk-Overlapping Deployment (DOD) Heuristic • Phase 2:Find the joint sectors of any two disks in . • the distance between their centers is no larger than 2rs • both disks have more thansectors • Whendrawing a circle between the two disks with a radius of rs,each disk has at least one sector whose objects all locateinside the circle Sector C Sector B Sector E Sector G Sector A disk da disk db Sector D Sector F Sb Sa

28. Disk-Overlapping Deployment (DOD) Heuristic • Phase 2:Find the joint sectors of any two disks in . • the distance between their centers is no larger than 2rs • both disks have more thansectors • Whendrawing a circle between the two disks with a radius of rs,each disk has at least one sector whose objects all locateinside the circle • joint sectors : Sector A, Sector B, Sector E • Non-joint sectors : Sector C, Sector D, • Sector F , Sector G Sector C disk da disk db Sector B Sector E Sb Sa Sector G Sector A Sector D Sector F

29. Disk-Overlapping Deployment (DOD) Heuristic • Phase 3: Calculate the additional disks used to cover the joint sectors. • disk di in withoutjoint sectors : deploy sensors to cover all of its sectors. ( : the number of non-joint sectors in di) diskdi Si

30. Disk-Overlapping Deployment (DOD) Heuristic • Phase 3: Calculate the additional disks used to cover the joint sectors. • disks in with joint sectors : • joint sectors : Sector A, Sector B, Sector E • Non-joint sectors : Sector C, Sector D, • Sector F , Sector G Sector C Sector B Sector E Sb Sa Sector G Sector A disk da disk db Sector D Sector F : cover all of its non-joint set sectors in di . : the max. number of sectors which every sensor can cover .

31. Disk-Overlapping Deployment (DOD) Heuristic • Phase 3: Calculate the additional disks used to cover the joint sectors. • disks in remain only joint sectors : iteratively select the two overlapped disks in such that their joint sectors have the maximum number of objects. Sector B Sector C Sector E Sb Sa Sector G Sector A disk da disk db Sector D Si Sector F Sector cutting operation

32. Maintaining the network connectivity • our deployment heuristics focus on covering all objects, but the network may not be connected. • we add extra relay nodes to maintain the network connectivity. [44] X. Han, X. Cao, E.L. Lloyd, and C.C. Shen, “Deploying directional sensor networks with guaranteed connectivity and coverage,” Proc. IEEE Conf. Sensor, Mesh and Ad Hoc Comm. and Networks, pp. 153–160, 2008.

33. Performance Evaluation • Simulator : C++ • Sensing field : 400 x 400 • Placement of static objects : random、congregation distributions • rs = 10, rc = 20 • n = 5 • Objects(m), sector angle , and value are varied.

34. Performance Evaluation • Effect of Different Object Numbers =45o congregatingdistribution of objects randomdistribution of objects

35. Performance Evaluation • Effect of Different Sector Angles

36. Performance Evaluation • Effect of Different Sector Angles

37. Performance Evaluation • Effect of DifferentValues =30o

38. Conclusions • In this paper, we have defined a temporal coverage model to monitor objects. • Two efficient heuristics are proposed : • MCD deploys sensors to cover the disks with more objects. • DOD deploys sensors to cover joint sectors to exploit disk overlap.