Direct movement has long relocation time and overuses the redundant sensor

1. sensing range M M $ for 90% coverage $ for 98% coverage C C B B B B A A B B Become strategic area Initialization • Static sensor: • broadcast location • Mobile sensor • base price = 0 M M N N Movement-Assisted Sensor Deployment and Sensor Relocation Guiling Wang, Dr. Guohong Cao, and Dr. Tom La Porta (guiwang, gcao, tlp@cse.psu.edu) Motivation • New event or new interest • Sensor failure • Deploying more static sensors cannot solve the problem due to wind or obstacles • Coverage!! Coverage under random deployment Coverage under clustering Solution: utilizing Mobile Sensor! Sensor Deployment Sensor Relocation direct the movement of sensors to increase coverage General idea: detecting coverage hole  move to heal the hole Objectives: • Least affect to applications (topology) • Short relocation time • Energy efficient and load-balanced Coverage Hole Detection Coverage hole detection: Only check local Voronoi cell • Utilizing Voronoi diagram: • Composed by the bisectors of neighbor sensors • Each point in a Voronoi cell is closer to the sensor in this cell than any other sensors • If the sensor can not detect the events happened in its Voronoi cell , no other sensors can Solution: Discover redundant sensors  only move the redundant sensors and cascading (relay) sensors if needed Redundant Sensor Discovery • Organize sensors in one grid into a cluster • Cluster head detects redundant sensors and maintains the information All the sensors are mobile Supply quorum GridQuorum system Coverage hole exists? Calculate the target location (by VEC, VOR or Minimax) • demand quorum: grids in a column • supply quorum: grids in a row • need sensor: search demand quorum • have redundant sensor: notify supply quorum Move VEC VOR Minimax • Move towards the farthest Voronoi vertex • Avoid moving oscillation: stop for one round if move backwards Move to where the distance to the farthest voronoi vertex is minimized • Motivated by the attributes of electrical particles • Virtual force pushes sensors away from dense area Demand quorum Movement Arrangement Redundant sensor Why cascading movement? A mix of mobile and static sensors Direct movement has long relocation time and overuses the redundant sensor Why mixed: tradeoff between coverage and sensor cost Bidding Protocol Service advertisement Strategy: make a cascading schedule  move following the schedule (movement is more costly than communication!) • Mobile sensor: hole-healing server • Base price:the coverage hole generated by their leaving • Static sensor: bidder • Bids: estimated size of the detected coverage hole Mobile sensor: • Broadcast <base price,location> Redundant sensor Which cascading schedule? Good! Bidding Serving Static sensor: • Send <bid, target location> to the closest mobile sensor • Bid > base price Mobile sensor: • Choose the highest bid • Move • Base price= accepted bid Much more energy consumption • Goals: • satisfy the requirement of relocation delay • minimize the difference between total energyconsumption and minimum remaining energy • Approach: • distributed implementation of dynamic programming Base price increases monotonically and protocol stops naturallywhen no bidding message is flying Tradeoff between Sensor Cost and Coverage Money needed for certain Coverage (Static sensor: $1; Mobile sensor: $n) • Guiling Wang, Guohong Cao, and Tom La Porta, “Movement-Assisted Sensor Deployment”, IEEE INFOCOM’04, March 2004. • Guiling Wang, Guohong Cao, and Tom La Porta, “A Bidding Protocol for Sensor Deployment”, IEEE ICNP’03, Nov., 2003. • Guiling Wang, Guohong Cao, and Tom La Porta,“Sensor Relocation in Mobile Sensor Networks”, in submission. Sensor needed for certain Coverage Industry Day 2004 @ NET-CENTER.PSU