1. A Novel Virtual Anchor Node- based Localization Algorithm for Wireless Sensor Networks Pengxi Liu, Xinming Zhang, Shuang Tian, Zhiwei Zhao, Peng Sun Department of Computer Science and Technology University of Science and Technology of China International Conference on Networking 2007

2. Outline Introduction Error analysis of typical localization algorithms Virtual Anchor Node-based Localization Algorithm (VANLA) Performance evaluation Conclusion

3. Introduction WSNs usually are arranged at special scout region, and sense special physics information in the region. Sensor nodes are often deployed by random bestrewing. The application of WSNs is often related to the positions of nodes. So the localization of sensor nodes has become a hot topic in WSNs.

4. Introduction Most of the existent researches suppose The network includes a small number of anchor nodes. The existence of various errors The location precision will be restricted Some nodes even cannot be located. The improvement of localization precision with lower cost less energy consumption less hardware support

5. Introduction The new algorithm finds out virtual anchors to provide highly precise positions for unknowns nodes to assist in locating the rest unknowns along with primary real anchors.

6. Error analysis of typical localization algorithms The authors choose two concrete algorithms to carry out error analysis. Euclidean Range-Based DV-hop Range-Free

7. Error analysis of typical localization algorithms - Euclidean Each sensor has ability to measure their relative distance. A B C L1 D α β L3 L2

8. Error analysis of typical localization algorithms - Euclidean The draw back of Euclidean The ranging error is the main flaw of Range-based algorithm. This error can be accumulated hop by hop.

9. Error analysis of typical localization algorithms – DV-hop DV-hop Use the corrected factor c i to fixed the hop distance. A B C X cAcA

10. Error analysis of typical localization algorithms – DV-hop The draw back of DV-hop In practical application, the communication range of each node is not a standard circle ideally.

11. Error analysis of typical localization algorithms – DV-hop A BC n-hop n*rn*r/2 The corrected factor is (3n*r/2*2n)=3r/4 Distance AC is n* 3r/4 =3n*r/4 The error is n*r-(3n*r/4)=n*r/4 This error can be accumulated hop by hop.

12. Virtual anchor node-based localization algorithm There can be only a few anchor nodes deployed in the network due to high cost and energy issue Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node The Upgrade of Virtual Anchor Node

13. Virtual anchor node-based localization algorithm Assumption The WSN is a dense network There are few anchor node in the network The shape of the path with the smallest hop count is asymptotic to a beeline

14. Virtual anchor node-based localization algorithm Scenario A C B D UEUE y

15. Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node A B C Hop A =1 x Compare Hop with “Hop A =n A ” If the hop has not received or is smaller than present hop Store Hop A =n A Hop A =n A Hop B =n B Hop C =n C Hop A =n A Hop B =0 Hop C =n C D

16. Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node A B C Hop A =n A Hop B =0 Hop C =n C Hop D =n d y Hop A =A y Hop B =B y Hop C =C y Hop D =D y IF A y +B y =n A candidate virtual anchor D

17. Virtual anchor node-based localization algorithm A B If Max(hop A, hop B ) – Min(hop A, hop B )= shortest path AB, it is also an candidate anchor y Hop A =n A Hop B =n B n AB nBnB n A = n AB +n B n A - n B =n AB

18. Virtual anchor node-based localization algorithm The Selection of Virtual Anchor Node A B C D

19. Virtual anchor node-based localization algorithm The Upgrade of Virtual Anchor Node A B C D UEUE

20. Virtual anchor node-based localization algorithm A C B D UEUE Node U E can upgrade as a anchor node

21. Virtual anchor node-based localization algorithm Node U E can upgrade as a anchor node W Y X Z UHUH UFUF UGUG

22. Virtual anchor node-based localization algorithm A C B D UEUE Calculate U E ’ s position (Xb,Yb)(Xb,Yb) (Xa,Ya)(Xa,Ya) (Xd,Yd)(Xd,Yd) (Xc,Yc)(Xc,Yc) (Xe,Ye)(Xe,Ye)

23. Virtual anchor node-based localization algorithm A C B D UEUE Calculate U E ’ s position F G

24. Performance evaluation Compiler: oCaml Language: caml OS: Cygwin

25. Performance evaluation Random deployment Field:32000m x 32000m Radius: 2200m 500nodes Ranging error 20%~50%

26. Performance evaluation

30. Random deployment Field:10000m x 10000m Radius: 2100m 500nodes

31. Performance evaluation

32. Conclusion In this paper, the authors proposed a distributed algorithm for virtual anchor nodes upgrading it can increase the density of virtual anchor nodes at low physical cost assist some algorithms which already exist to enhance the precision of localization in the network with dense nodes