1 Review: Mobile Sensor Networks An Overview prepared by Y.C. Wang and Y.C. Tseng

2 Introduction As sensors become widely deployed, some sensors may be enhanced with mobility. Such mobile sensors may be more powerful and can re-charge themselves automatically. An important application is in the robot area. Why need mobile sensors? Resilient to failures Reactive to events Support disparate missions

3 Research Directions on Mobile Sensor Networks Improve network topology WSN deployment WSN fault diagnosis Enhance sensing in WSN Enhance routing in WSN Applications

4 Improve Network Topology (1/2) Make a stronger network P. Basu and J. Redi, Movement control algorithms for realization of fault-tolerant ad hoc robot networks, IEEE Network, vol. 18, no. 4, pp. 36 – 44, Find out cut-vertices and move sensors around to make the network biconnected. cutvertex

5 Improve Network Topology (2/2) Enhancing an existing WSN S. Zhou, M. Y. Wu, and W. Shu, Finding optimal placements for mobile sensors: wireless sensor network topology adjustment, in IEEE Circuits and Systems Symposium on Emerging Technologies: Frontiers of Mobile and Wireless Communication, 2004, pp. 529 – 532. Randomly drop sensors may not guarantee a connected network Add mobile sensors to connect separated components Static sensors

6 WSN deployment (1/3) Virtual force Y. Zou and K. Chakrabarty, Sensor deployment and target localization based on virtual forces, in IEEE INFOCOM, 2003, pp – A sensor s i will be exerted by three kinds of forces An attractive force by the deployed area A repulsive force by all obstacles A force by another sensor s j (is expressed by polar coordinate notation ) w A /w R : measure of the attractive/repulsive force d th : a threshold distance moving direction of S1

7 WSN deployment (2/3) Voronoi diagram G.Wang, G. Cao, and T. L. Porta, Movement-assisted sensor deployment, in IEEE INFOCOM, 2004, pp – Use Voronoi diagram to find potential coverage holes and move sensors to cover these holes Voronoi diagram Node v is farthest to the vertex u, so it moves in that direction.

8 WSN deployment (3/3) Grid structure G. Wang, G. Cao, T. L. Porta, and W. Zhang, Sensor relocation in mobile sensor networks, in IEEE INFOCOM, 2005, pp – Grid-quorum A high-density grid sends Advertisements along its row A low-density grid sends Requests along its column Cascaded movement A direct (long) movement can be decomposed into multiple (short) movements. This can achieve better fairness.

9 WSN Diagnosis Bidding Protocol G. Wang, G. Cao, and T. L. Porta, A Bidding Protocol for Deploying Mobile Sensors, in IEEE Int l Conf. on Network Protocols, 2003, pp. 315 – 324. Static sensors estimate coverage holes, and then use hole sizes to compete for mobile sensors to move in.

10 Enhance Sensity of WSN Event-based motion Z. Butler and D. Rus, Event-based motion control for mobile-sensor networks, IEEE Pervasive Computing, vol. 2, no. 4, pp. 34 – 42, Move more sensors closer to the event locations while still maintaining complete coverage of the field (1) Initial topology of the network (2) Determine event locations (3) Move sensors around so that event areas have higher sensor density. Complete coverage is maintained.

11 Enhance routing in WSN Mobile relay W. Wang, V. Srinivasan, and K. C. Chua, Using Mobile Relays to Prolong the Lifetime of Wireless Sensor Networks, in Mobicom, 2005, pp Use mobile relay to extend the lifetime for the bottleneck nodes. Example: sensors A and B are rotated in routing packets.

12 Applications Pursuer-evader problem C. Sharp, S. Schaffert, A. Woo, N. Sastry, C. Karlof, S. Sastry, and D. Culler, Design and implementation of a sensor network system for vehicle tracking and autonomous interception, in European Workshop on Sensor Networks, 2005, pp. 93 – 107. The evader will randomly move in the sensing field The pursuer can capture the evader by the information from the static WSN static sensor evader pursuer