1. On Mobile Sink Node for Target Tracking in Wireless Sensor Networks Thanh Hai Trinh and Hee Yong Youn Pervasive Computing and Communications Workshops(PerComW'07)

2. Outline Introduction The Related Work The Proposed Scheme Performance Evaluation Conclusion

3. Introduction As the sensed data are forwarded to the sink node in the WSN The sensor nodes close to the sink (moles) have to relay a large amount of data received from other nodes mole

4. The Related Work A mobile robot can be used as a sink to collect information in target tracking applications [1] Scalable Energy-efficient Asynchronous Dissemination protocol (SEAD) [2] is given to establish and manage a data dissemination tree from source to mobile sink The two-tier scheme was proposed to provide scalable and efficient data delivery to mobile sinks [3] Wang et al. [4] have used a linear programming approach to determine the optimal movement of the sink

5. The Two-Tier Scheme Unicast (Geographic Forwarding) Minimum Spanning Tree mole Two-Tier Data Dissemination  Dense sensor network

6. The problem The moles consume their batteries much faster than other nodes and limit the lifetime of the entire network One solution for this problem is to let the sink move

7. The Proposed Scheme A cluster of sensors Formed around the target Collect the information in multi-hop communication Using the target information the sink moves toward the target Reducing the communication cost Saving the energy of moles

8. Assumptions Tracking a single target Multi-hop data transmission between the source and sink A single sink with unlimited battery power If the distance between two nodes exceeds h (the hop length), they cannot be neighbors

9. Initialize :exchange the information of the neighbor nodes every node broadcasts a message to inform its identity 5 1 3 4 S2 6 7

10. Initialize :exchange the information of the neighbor nodes When a node receives a packet from its neighbor node, it stores the ID and location of it in a table 5 1 3 4 S2 6 7

11. Form hop-count table The sink broadcasts an ANNOUNCEMENT message containing the Hop-Count (HC) field. This field is used to denote the hop distance to the sink. 5 1 3 4 S2 6 7 ANNOUNCEMENT

12. Form hop-count table When a sensor node receives the message originated from the sink, it increments the Hop-Count by 1 and forwards the message to its neighbor nodes. 5 1 3 4 S2 6 7 HC=1

13. Form hop-count table This process continues until all the nodes decide the shortest path to the sink in terms of Hop-Count 5 1 3 4 S2 6 7 HC=1 HC=2 HC=3

14. Form hop-count table Then, they notify the sink of their information through the path and turn back to hibernation mode to save the energy. 5 1 3 4 S2 6 7 HC=1 HC=2 HC=3

15. Form hop-count table Finally, the sink stores the locations and IDs of entire sensor nodes in its table. 5 1 3 4 S2 6 7 HC=1 HC=2 HC=3 idHC 11 21 32 42 52 63 73

16. Determine A Cluster: the nodes detecting a target Assume that the nodes detecting a target form a cluster, A s E i (t) ： The power of target signal at node-i E thres,i ： The detection threshold of node-i L i denotes the location coordinates L t (t) denote the location coordinates of the target R is the parameter representing the signal range of the target

17. The power of target signal at node-i E i (t), is estimated in the following equations where

18. The detection threshold of node-i E thres,i can be acquired by where

19. The cluster head election process Initially, node-i find adjacent sensor nodes in the cluster Then, node-i sends a message to the nodes belonging to A t Hop-Count Remaining energy After a random time interval, if it does not receive any message from node-k {k| k Є At, E k <Ei}, it sends a message declaring itself as the cluster head of the cluster A t.

20. The cluster head election process 6 5 1 m 4 2 3 s m m HC=4, E=130 HC=5, E=150 HC=6, E=120 HC=4, E=15 HC=5, E=135 HC=6, E=123 7

21. The cluster head election process 6 5 1 m 4 2 3 s m m HC=4, E=130 HC=5, E=150 HC=6, E=120 HC=4, E=15 HC=5, E=135 HC=6, E=123 7

22. Target Information: The Average Error N t =|A t | sensor nodes Locations L i = (x i, y i ), i = 1,…N t. Location of the target at time t L e (t)=(x e (t),y e (t)) The average of the N t positions For the time T spent by a target in the area of interest, the average error Q, is given by

23. The Sink Movement After the sink estimates the location of the target, it moves toward it during T track. At the new location, if the sink lost the connection with the current mole Broadcasts the FIND_NEAR_MOLE message to search for another mole nearby All nodes receiving the message send a reply message containing the remaining energy. Then, the sink updates the table using the process mentioned above

24. Example Sink Mole Cluster head

25. Example Sink Mole Cluster head

26. Performance Evaluation Developed a simulator : C++ 1000 nodes deployed randomly in the 200 x 200m monitoring area velocity of target: 20m/s velocity of sink: 10m/s T track = 5s, R = 10m, and h = 7m Energy of sensor: 1000 units The cost of sending or receiving a packet: 1 unit

27. The total energy consumption

28. The number of remaining sensor nodes

29. Conclusion A mobile sink for target tracking applications to prolong the network lifetime Relocating the sink toward the target to minimize the communication cost Computer simulation reveals that the proposed scheme ensures a much longer network life time than the approach with fixed, circular, and random moving sink node

30. Future work Considers more complex circumstances such as multiple targets and sink nodes.

31. Thank you