1. Distributed Localization Using a Moving Beacon in Wireless Sensor Networks IEEE Transactions on Parallel and Distributed System, Vol. 19, No. 5, May 2008 + Bin Xiao, + Hekang Chen and *Shuigeng Zhou + Department of Computing, Hong Kong Polytechnic University, Hong Kong. * Department of Computer Science and Engineering, Fudan University.

2. Outline  Introduction  Distributed Localization using a Moving Beacon  Movement Patterns of the Beacon  Localization in the Real Environment  Performance Evaluation  Conclusions

3. Introduction  The techniques used to identify the position of each sensor node are central to such location-aware operations. where events take place tracking moving targets assisting traffic routing providing the network geographic coverage

4. Introduction  It is not infeasible to equip each node in a network with a Global Positioning System. Constraints of cost and power consumption  Sensor nodes may be used to identify the position of other nodes in a sensor network. Range-based Range-free

5. Introduction  In this paper, the authors propose distributed method to localization of sensor nodes low hardware cost use moving beacon feasible and accurate

6. Distributed Localization – using a Moving Beacon Static sensor Moving beacon

7. Distributed Localization – using a Moving Beacon Static sensor Moving beacon arrival position prearrival position departure position post departure position Arrival and Departure Overlap (ADO)

8. Distributed Localization – using a Moving Beacon Static sensor Moving beacon

9. Movement Patterns of the Beacon  Sparse-Straight-Line (SSL)  Dense-Straight-Line (DSL)  Random movement pattern

10. SSL Movement Patterns

11. Arrival and Departure Overlap (ADO) upper HADO lower HADO

12. Distributed Localization – using a Moving Beacon Static sensor Moving beacon upper HADO lower HADO

13. SSL Movement Patterns Moving beacon

14. B SSL Movement Patterns Line 1 Line 2 Line 3 B  Rule 1. If B is in the row immediately above the ( i -1)th line, the position of A is below the i th line. Moving beacon

15.  Rule 2. If HADO(B) cannot contact HADO upper (A), the position of A is below the i th line. SSL Movement Patterns Line 1 Line 2 Line 3 A A’ Moving beacon

16. SSL Movement Patterns Line 1 Line 2 Line 3 C  Rule 3. If HADO(C) can contact HADO upper (A), the position of A is below the i th line. A A’ Moving beacon

17. DSL Movement Patterns Moving beacon

18. Uncovered Space Moving beacon

19. Random movement pattern A Static sensor Moving beacon (previous position, current position, next position) (prearrival, arrival, departure, postdeparture)

20. Random movement pattern  The overlap of ADOs creates a single kernel overlap area ( KOA )  Suppose that the KOA consists of n vertices. Let the coordinates of those n vertices (from v 1 to v n ) be (x 1, y 1 ), (x 2, y 2 ),..., (x n, y n )

21. Random movement pattern  If node G can acquire the information of k ADOs k prearrival positions k arrival positions k departure positions k postdeparture positions  OutPoints as a set to encompass both the prearrival and postdeparture positions  InPoints as a set to encompass both the arrival and departure positions  Point set P contain all the intersection points of these 4k circles.

22. Random movement pattern  Given a point u in P, its initial degree is set to 0. If the distance between u and an InPoint is not more than r, its degree is increased by 1 If the distance between u and an OutPoint is not less than r, its degree is increased by 1

23. Localization in the Real Environment Out of range Arrival position In range

24. Performance Evaluation  300 nodes  500 m x 500 m  Transmission range r ： 30~50 m  Beacon interval s ： 1~9 m

25. Comparisons of the Three Movement Patterns SSLDSL Random

26. General Performance Comparison

27. Detailed Estimate Error Information s = 0.3 m s = 0.6 m

28. Percentage of accurately localized nodes

29. Communication overhead

31. Conclusions  The authors present a distributed range-free localization method use only one moving beacon feasible and accurate  The basic idea is to narrow down the possible location of a node use the arrival and departure constraint SSL pattern DSL pattern Random movement pattern

32. Thank You ~