Review: Mobile Sensor Networks

1
ReviewMobile 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.
  3644, 2004.
• Find out cut-vertices and move sensors around to
  make the network biconnected.

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. 529532.
• 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. 12931303.
• A sensor si 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 sj (is expressed
  by polar coordinate notation )

moving direction of S1
wA/wR measure of the attractive/repulsive
force dth a threshold distance
7
WSN deployment (2/3)

• Voronoi diagram
• G.Wang, G. Cao, and T. L. Porta,
  Movement-assisted sensor deployment, in IEEE
  INFOCOM, 2004, pp. 24692479.
• 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. 23022312.
• 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
  Intl Conf. on Network Protocols, 2003, pp.
  315324.
• 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. 3442, 2003.
• 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. 270-283.
• 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.
  93107.
• The evader will randomly move in the sensing
  field
• The pursuer can capture the evader by the
  information from the static WSN