1. Younghwan Yoo† and Dharma P. Agrawal‡ † School of Computer Science and Engineering, Pusan National University, Busan, KOREA ‡ OBR Center for Distributed and Mobile Computing, Department of CS University of Cincinnati, USA IEEE Vehicular Technology Conference, 2008 (Spring) 2016/3/6I-Hsin Liu

2.  Introduction  Energy-Considered Virtual Force Algorithm (EVFA)  Simulation  Conclusion 2

3.  The Wireless Sensor Network (WSN) has recently attracted considerable attention. ◦ due to the low price and ease to deploy it.  But, in a hostile or harsh regions ◦ Sensors cannot be deployed manually. ◦ WSNs can be established just by dropping sensors from the air. 3

4.  In this case, however, most likely sensors are not placed at optimal positions. ◦ drastic impact on the WSN performance.  Ex: coverage and lifetime  Moreover, randomized deployment algorithm can have coverage holes in the sensing area. 4

5.  This paper proposes a sensor relocation scheme. ◦ Using mobile sensors to move to patch up the holes by appropriate coverage.  Using mobile sensor relocation scheme to prolong the lifetime of WSNs. ◦ by reducing unnecessary movement of sensors. 5

6.  Virtual Force Algorithm (VFA) ◦ Y. Zou and K. Chakrabarty, “Sensor Deployment and Target Localization Based on Virtual Forces,” in Proc. IEEE INFOCOM, 2003, pages 1293–1303. 6

7.  The force by sensor j on sensor i is computed as 7 W A and W R denote the attractive and the repulsive force

8.  The force by sensor j on sensor i is computed as 8 d i,j is the distance between i and j.

9.  The force by sensor j on sensor i is computed as 9 d th is the threshold of distance.

10.  The force by sensor j on sensor i is computed as 10 α i,j is the direction of vector.

11. 11 S1 S2 S3 S4

12. 12 S1 S2 S3 d th =2*TR d 13 =d th

13. S4 13 S1 S2 S3 d th =2*TR d 14 >d th

14. S4 14 S1 S2 S3 d th =2*TR d 14 >d th

15. S4 15 S1 S2 S3 d th =2*TR d 12 <d th

16.  VFA is a centralized algorithm ◦ All vector computations are performed by the sink. ◦ Sensors just move to positions finally specified by the sink.  This VFA is executed by round-by-round process to enhance coverage ratio. 16

17.  In the paper proposed Energy-considered Virtual Force Algorithm (EVFA).  EVFA has three major differences from VFA: ◦ The area exclusively covered by a sensor is proportional to its residual power. ◦ The area exclusively covered by a sensor is proportional to the distance from a sink to itself. ◦ A distributed algorithm. 17

18. 18 Related work VFA EVFA

19. 19 Related work VFA EVFA d th =2*TRd th =d 1 +d 2

20. 20 C. Bettstetter, “On the Minimum Node Degree and Connectivity of a Wireless Multihop Network,” in Proc. ACM MobiHoc, 2002.

21. 21 Ρ is the density in the sensor network C. Bettstetter, “On the Minimum Node Degree and Connectivity of a Wireless Multihop Network,” in Proc. ACM MobiHoc, 2002. n is the total number of sensor nodes A is the sensing area SR TR

22. 22 The min residual energy in A 1 k is the neighbor of S 1 A1A1

23. 23 The min residual energy in A 1 k is the neighbor of S 1 A1A1

24. 24 A1A1 The min distance between neighbor k and sink in A 1

25. 25 A1A1

26. Number of mobile node30 Sensing Area50*50 m 2 Transmission Range20 m Sensing Range6 m Packet size512 Bytes Energy consumption of transmit0.221 J Energy consumption of receive0.205 J Energy consumption of move 1 m27.96 J Initial energy of all sensors900~1000 J Total simulation time5000 sec 26

27. 27 EVFA W A =0.005, W R =0.0538.01% W A =0.005, W R =0.0236.72% W A =0.002, W R =0.05107.98%

28. 28

29. 29

30.  We proposed a mobile sensor relocation scheme to prolong the lifetime of WSNs by reducing unnecessary movement of sensors.  EVFA makes sensors with less energy or closer to a sink take charge of smaller sensing area. 30

31. 31 Thank You

32. 32 C. Bettstetter, “On the Minimum Node Degree and Connectivity of a Wireless Multihop Network,” in Proc. ACM MobiHoc, 2002. The sensing range of all nodes is r 0 The total number of nodes p is the density in the sensor network