Location Tracking in a Wireless Sensor Network by Mobile Agents and Its Data Fusion Strategies Yu-Chee Tseng, Sheng-Po Kuo, Hung-Wei Lee and Chi-Fu Huang The Computer Journal 2004 Special Focus-Mobile and pervasive computing Volume 47, Issue 4, July 2004: pp Bao-Hua Yang

Outline Introduction Network Model and Problem Statement The Location Tracking Protocol Fusion and Delivery of Tracking Results Prototyping Experiences and Simulation Results Conclusion

Introduction Many issues remain to be resolved for success of sensor network  Scalability Sensor network comprises a large number of nodes How to manage resources and information is not easy  Stability Be installed in outdoor or hostile environments Protocols should be stable and fault-tolerant  Power-saving Energy conservation should be kept in mind in all cases

Introduction Goal  Location tracking: to monitor the roaming path of a moving object An object is detected  A mobile agent will be initiated to track the roaming path The agent will choose the sensor closest to the object to stay

Network Model and Problem Statement

Network Model and Problem Statement--- Assumption In order to track objects’ location, the sensor should know:  Aware of its physical location  Aware of the neighbor physical location  The capability of compute and communication  Sensing scope: R = the side length of the triangles Object  Assume that sensors can distinguish one object from another

Network Model and Problem Statement Working area: A 0 Backup area: A 1,A 2,A 3

The Location Tracking Protocol --- Basic idea Master Slave2Slave1

The Location Tracking Protocol --- Basic idea Master Slave2 Slave1

The Location Tracking Protocol --- Basic idea Master Slave2 Slave1

The Location Tracking Protocol --- Basic idea Master Slave2 Slave1

The Location Tracking Protocol --- Protocol detail Status: Idle Bid_master (ID,sig)

The Location Tracking Protocol --- Protocol detail

S0S0 S2S2 S1S1

(1):Master will revoke all slaves and invite two new one (2):Master revoke slave S 1 and invite a new one (3):Master migrate itself to a sensor with strongest receive signals and revoke all slaves slave Master (4) (5) (6)

The Location Tracking Protocol --- Protocol detail

S0S0 S2S2 S1S1

S0S0 S2S2 S1S1

The Location Tracking Protocol --- Extension to irregular network topologies The election process does not need to be changes  Sensors can still bid for serving as a master/slave based on their signal strengths Only the rules to migrate masters/slaves need to be modified

The Location Tracking Protocol --- Extension to irregular network topologies Using Voronoi graphs to find the master and slaves (b)The Voronoi graphs after removing the master (c)The Voronoi graphs after removing the master and the first slave (a)The Voronoi graphs of all vertics

The Location Tracking Protocol --- Extension to irregular network topologies Working and backup areas Backup area Working area

Fusion and Delivery of Tracking Results Non-Agent-Based (NAB) strategy  Each sensor works independently and forward its sensing results back to the gateway Threshold-Based (TB) strategy SiSi S i+1 G (1)The amount of result < Threshold  carry (2)The amount of result > Threshold  forward 1 1 2

Fusion and Delivery of Tracking Results Distance-Based (DB) strategy  The distance from the agent’s current and next sensors to the gateway are considered

Fusion and Delivery of Tracking Results G iff C1 < C2 : the master agent will carry the results with it Otherwise: the results will be sent back to the gateway SiSi S i+1 Si decides to carry the tracking result with it: Si decides to deliver its current tracking result to the gateway: Ni=

Prototyping Experiences and Simulation Results Simulation environment  Sensing field: 10000m*10000m  Distance between two neighboring sensors:80m  Gateway is located at the center of the network  Object moves at a constant speed: 1~3m  Control packet, location information, packet header: 2 bytes

Prototyping Experiences and Simulation Results Experimental environment: (a)Triangular sensor network (b)Square sensor network

Prototyping Experiences and Simulation Results

Conclusion Proposed a location-tracking protocol for regular and irregular sensor network  Reducing communication and sensing overhead

The Location Tracking Protocol --- Protocol detail

Fusion and Delivery of Tracking Results

Prototyping Experiences and Simulation Results