1. Shibo He 、 Jiming Chen 、 Xu Li 、, Xuemin (Sherman) Shen and Youxian Sun State Key Laboratory of Industrial Control Technology, Zhejiang University, China 、 Department of Electrical and Computer Engineering, University of Waterloo, Canada INRIA Lille - Nord Europe, Univ Lille Nord de France IEEE INFOCOM 2012 Cost-Effective Barrier Coverage by Mobile Sensor Networks 1

2. Outline  Introduction  Goal  Assumption  Problem formulation  Periodic Monitoring Scheduling algorithm  Coordinated Sensor Patrolling algorithm  Distributed CSP  Simulation  Conclusion 2

3. Introduction  Wireless sensor networks have received a lot of attention due to their potential applications in various areas  Environmental monitoring  The placement of sensors related to coverage issues is intensively studied in the literature, and can be divided into three categories.  Target coverage  Full coverage  Barrier coverage 3

4. Introduction  The target coverage problem (Points of Interest, PoI)  aims at monitoring specific points in the field of interest. MuseumCampusMilitary 4

5. Introduction  The full coverage problem (Areas of Interest, AoI)  aims at covering the whole area.  Sensors are deployed to maximize the covered area. 5

6. Introduction  The barrier coverage problem  Aim at detecting intrusion on a given area.  Sensors have to form a dense barrier in order to detect each event that crosses the barrier. USA Intruder 6

7. Introduction  Existing solutions to barrier coverage in mobile sensor networks implicitly assume the availability of sufficient sensors.  K-barrier  One-barrier K-BarrierOne-Barrier 7

8. Introduction  These solutions will fail to work when sensor scarcity and budget limitation.  the performance of detecting intruder decreasing K-BarrierOne-Barrier 8

9. Goal  In the case of sensor scarcity, this paper proposed two algorithms to  Improve the probability of detecting intruder  Decrease sensor’s moving distance 9

10. Assumption  The belt region of interest Ω with two long parallel boundaries.  m sensors are needed to guarantee full barrier coverage but there are only n mobile sensors available (n < m). l Ω 10

11. Problem formulation  max γ while min L  Average intruder detection probability  Average sensor moving distance ： the state of intruder arrival ： the state of sensor presence at point i t t 0011 1 0011 0010001 00 10 the distance that sensor j moves in time t 11

12. Patrolling algorithms  Periodic Monitoring Scheduling  Coordinated Sensor Patrolling 12

13. Periodic Monitoring Scheduling  The basic idea of PMS is to let the sensors monitor each point periodically.  there are m points, but only have n (n<m)mobile sensors to monitor.  sensor at point j moves to point mod(j + n, m) and sensing the point for T time slots. 01234 ABC A A A A B B B B C C C C t0t0 t1t1 t2t2 t3t3 t4t4 01234012340123401234 13 B 2  mod(2+3,5)=0  mod(0+3,5)=3  mod(3+3,5)=1  mod(1+3,5)=4

14. Periodic Monitoring Scheduling  The basic idea of PMS is to let the sensors monitor each point periodically.  Presenting PMS algorithm to solve barrier coverage problem formulated  Average intruder detection probability  Average sensor moving distance 14

15. Periodic Monitoring Scheduling  Average intruder detection probability the steady-state probability of intruder arrival at each slot 15

16. Periodic Monitoring Scheduling  Average sensor moving distance proof ： the minimum scheduling period ： How many time slots that each point is monitored by sensors ： How many time slots in the monitoring period sensor’s moving distance when j+n > m sensor’s moving distance when j+n <= m 16

17. Patrolling algorithms  Periodic Monitoring Scheduling  Coordinated Sensor Patrolling 17

18. Coordinated Sensor Patrolling  A centralized coordinated sensor patrolling algorithm.  Exploiting the temporal correlation of intruder arrival times to improve average intruder detection probability γ. 18

19. Coordinated Sensor Patrolling  Intruder arrival analysis t=1 t=2 τ τ+1 τ+2 one intruder arrives at slot τ +2 two intruders arrive,one at slot τ +1 and the other is τ +2 the probability that the next intruder arrival is at slot τ +t given the last intruder arrival time is τ. Cumulative Distribution Function 19

20. Coordinated Sensor Patrolling  Intruder arrival analysis  After an intruder arrives at a point, the probability that an intruder will arrive again at the same point in the next few time slots is very small. 20

21. Coordinated Sensor Patrolling  Point selection step  Coordinated movement step 21

22. Coordinated Sensor Patrolling  Point selection step  Three principles  A sensor should move to another point if it detects an intruder at the point in the previous time slot.  A sensor should not leave its current point until it detects an intruder. 0 1 2 3 4 A A Available 22 B B Unavailable

23. Coordinated Sensor Patrolling  Point selection step  Three principles  A sensor should move to another point if it detects an intruder at the point in the previous time slot.  A sensor should not leave its current point until it detects an intruder  The points with highest q t should be selected if a sensor wants to find a point to monitor. 23 ： the number of time slots that there is no sensor at point j &

24. Coordinated Sensor Patrolling  Coordinated movement step  In order to reduce the total moving unavailable sensors do not necessarily stay at their previous points distance of each sensor. 24 t0t0 0123401234 t1t1

25. Distributed CSP  Distributed variants  Simple DCSP 25

26. Distributed CSP  Simple DCSP  Initialization phase  Dynamic movement phase 26

27. Simple DCSP  Initialization phase  The leader  Indicating how the sensor likes to monitor the points.  distribute the preference level of each sensor among the points.  Assign a preference level to points 0 1 2 3 4 AB C A 27

28. Simple DCSP  Initialization phase 0 1 2 3 4 A m=5,n=3 ABC 01234 A 0 A 1 28

29. Simple DCSP  Initialization phase 0 1 2 3 4 A B C A B B C 29

30. Simple DCSP  Dynamic movement phase  A sensor should not leave its current point until it detects an intruder.  Sensor moves to the new point with high  Each sensor moves between points in MS i  Collision problem 30

31. Simple DCSP  Dynamic movement phase  Collision problem  it will set I ij = 0 and recalculate  Sensor i and sensor i+1 generate random number from and exchange their number 0 1 2 3 4 B C A A 31

32. Simulation  Using MATLAB to perform the simulation  The network operation time is divided into time slots, each with 1 unit simulated time. 32

33. Simulation  Performance of PMS  Average intruder detection probability v.s. T slots 33

34. Simulation  Performance of CSP  Average intruder detection probability v.s. number of sensor 34 Performance γ for different n and m when β = 4.

35. Simulation  Average intruder detection probability v.s. number of sensor 35 when β = 2when β = 6

36. Conclusion  In the case of sensor scarcity, this paper proposed  Periodic monitoring scheduling algorithm  Coordinated sensor patrolling algorithm  reduce the application budget.  provides a new cost-effective approach to achieve barrier coverage in large-scale mobile sensor networks. 36

37. 37 Thank you