1. HCRL: A Hop-Count-Ratio based Localization in Wireless Sensor Networks Sungwon Yang, Jiyoung Yi and Hojung Cha Department of Computer Science, Yonsei University, Korea SECON 2007

2. Outline Introduction HCRL Mechanism Experiments Conclusion and future work

3. Introduction In WSNs, determining the positions of nodes is essential in many applications. EX. Coverage, Routing, Target tracking and etc. Localization is a fundamental component of sensor networks The cost for localization itself should be minimized

4. Introduction – DV-Hop y A C B A, Hop n 1 B, Hop n 2 C, Hop n 3 B, Hop n 9 C, Hop n 8 cAcA Average Hop Distance: c A DV-Hop needs flooding message twice. Sensor node Anchor node

5. Introduction - Goal In this paper, the author focus on developing a localization algorithm which provides both low-cost and accuracy. The authors aim to develop a localization scheme which requires less packet exchanging.

6. HCRL mechanism Assumption There are at least four anchor nodes in the network. HCRL only needs single flooding. Each sensor can control its transmitting power.

7. HCRL mechanism Apollonius Circle AP:BP=m:n, m≠n P O(x o,y o ) B(x B,y B ) A(x A,y A ) I(x I,y I ) E(x E,y E ) α α β β m n 2α+2β=180 o => α+β=90 o

8. HCRL mechanism – Basic

10. y A D B A, 2, (x A,y A ) B, 5, (x B,y B ) C, 3, (x C,y C ) D, 4, (x D,y D ) Sensor node Anchor node C

11. 43 HCRL mechanism – Basic IDHop ABCDABCD 43254325 y A D B C I AB y’ (30,40)(50,70) （ 41.43,57.14 ） E AB (110,160) O AB (75.72,108.57)

12. HCRL mechanism – Basic 500m x 500m random deployment Transmission range is 60m

13. HCRL mechanism - improved w x y z HC=1 HC=2 HC=3

14. HCRL mechanism - improved How the unknown node U5 collects the information?

15. HCRL mechanism - improved 500m x 500m random deployment Transmission range is 120m

16. Experiments Sensors: 36 Tmote Sky 4 anchor nodes on the verge of experimental field 32 normal nodes Comparison DV-Hop HCRL without subdivision HCRL with 2 subdivision

17. Experiments Average RSS vs. distance in an obstacle-free environment. The top of antenna is at a height of (a) 20cm and (b) 60cm.

18. Experiments (a) Grid network topology (b) random network topology

19. Experiments Localization error in grid topology The performance of each scheme was almost same.

20. Experiments Localization error difference in grid topology.

21. Experiments Localization error in random topology

22. Experiments Localization error difference in random topology

23. Conclusion and future work In this paper, the authors proposed a low cost and provided better localization accuracy. In the future, they plan to develop an environment-independent HCRL scheme.

24. END