Distributed Localization Using a Moving Beacon in Wireless Sensor Networks IEEE Transactions on Parallel and Distributed System, Vol. 19, No. 5, May Bin Xiao, + Hekang Chen and *Shuigeng Zhou + Department of Computing, Hong Kong Polytechnic University, Hong Kong. * Department of Computer Science and Engineering, Fudan University.

Outline  Introduction  Distributed Localization using a Moving Beacon  Movement Patterns of the Beacon  Localization in the Real Environment  Performance Evaluation  Conclusions

Introduction  The techniques used to identify the position of each sensor node are central to such location-aware operations. where events take place tracking moving targets assisting traffic routing providing the network geographic coverage

Introduction  It is not infeasible to equip each node in a network with a Global Positioning System. Constraints of cost and power consumption  Sensor nodes may be used to identify the position of other nodes in a sensor network. Range-based Range-free

Introduction  In this paper, the authors propose distributed method to localization of sensor nodes low hardware cost use moving beacon feasible and accurate

Distributed Localization – using a Moving Beacon Static sensor Moving beacon

Distributed Localization – using a Moving Beacon Static sensor Moving beacon arrival position prearrival position departure position post departure position Arrival and Departure Overlap (ADO)

Distributed Localization – using a Moving Beacon Static sensor Moving beacon

Movement Patterns of the Beacon  Sparse-Straight-Line (SSL)  Dense-Straight-Line (DSL)  Random movement pattern

SSL Movement Patterns

Arrival and Departure Overlap (ADO) upper HADO lower HADO

Distributed Localization – using a Moving Beacon Static sensor Moving beacon upper HADO lower HADO

SSL Movement Patterns Moving beacon

B SSL Movement Patterns Line 1 Line 2 Line 3 B  Rule 1. If B is in the row immediately above the ( i -1)th line, the position of A is below the i th line. Moving beacon

 Rule 2. If HADO(B) cannot contact HADO upper (A), the position of A is below the i th line. SSL Movement Patterns Line 1 Line 2 Line 3 A A’ Moving beacon

SSL Movement Patterns Line 1 Line 2 Line 3 C  Rule 3. If HADO(C) can contact HADO upper (A), the position of A is below the i th line. A A’ Moving beacon

DSL Movement Patterns Moving beacon

Uncovered Space Moving beacon

Random movement pattern A Static sensor Moving beacon (previous position, current position, next position) (prearrival, arrival, departure, postdeparture)

Random movement pattern  The overlap of ADOs creates a single kernel overlap area ( KOA )  Suppose that the KOA consists of n vertices. Let the coordinates of those n vertices (from v 1 to v n ) be (x 1, y 1 ), (x 2, y 2 ),..., (x n, y n )

Random movement pattern  If node G can acquire the information of k ADOs k prearrival positions k arrival positions k departure positions k postdeparture positions  OutPoints as a set to encompass both the prearrival and postdeparture positions  InPoints as a set to encompass both the arrival and departure positions  Point set P contain all the intersection points of these 4k circles.

Random movement pattern  Given a point u in P, its initial degree is set to 0. If the distance between u and an InPoint is not more than r, its degree is increased by 1 If the distance between u and an OutPoint is not less than r, its degree is increased by 1

Localization in the Real Environment Out of range Arrival position In range

Performance Evaluation  300 nodes  500 m x 500 m  Transmission range r ： 30~50 m  Beacon interval s ： 1~9 m

Comparisons of the Three Movement Patterns SSLDSL Random

General Performance Comparison

Detailed Estimate Error Information s = 0.3 m s = 0.6 m

Percentage of accurately localized nodes

Communication overhead

Conclusions  The authors present a distributed range-free localization method use only one moving beacon feasible and accurate  The basic idea is to narrow down the possible location of a node use the arrival and departure constraint SSL pattern DSL pattern Random movement pattern

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