Cooperative Location-Sensing for Wireless Networks Charalampos Fretzagias and Maria Papadopouli Department of Computer Science University of North Carolina at Chapel Hill PerCom 2004 IEEE International Conference on Pervasive Computing and Communications, March 2004 Bao-Hua Yang

Outline  Introduction  Cooperative Location-Sensing  Performance analysis  Conclusion

Introduction  To support location-dependent services, a device needs to estimate its position  How to estimate the position of devices? GPS  Breaks down near obstacles (trees, buildings)  Does not work indoors  Not cost-effective  Not suitable for small and energy-constrained devices  e.g.: PDA, sensor … Other algorithms

Introduction 1 a b c Positioning by triangulation

Introduction 1 Positioning by triangulation a b c Measuring distance by RF signal strength

Introduction 1 a b c 1 a b c Ideal situation real situation Positioning by triangulation

Introduction --- Assumption  Radio propagation Convert a signal strength value to a distance interval (d-e, d+e), where e is range error 1 d a

Introduction --- Assumption  Assume that all host are stationary during CLS run  Node are randomly placed  Landmark know its position  Hosts don ’ t know position

Introduction  The following design characteristics shape the vision for cooperative location-sensing Robust Computationally inexpensive Suitable for indoor and outdoor environment Scalable and easily deployable

Cooperative Location-Sensing

Communication protocol Voting process

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4

L1L1 L2L2 L3L3 L4L4 CLS beacon: 1.Namely 2.Position 3.Voting weight 4.Max. transmission range 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 CLS beacon: 1.L 4 2.Position of L 4 3.Voting weight: 2 4.Max. transmission range 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Cooperative Location-Sensing  Two threshold ST:  The number of votes in each cell of the potential solution must be above a threshold LECT:  The number of cells with maximal value must be below a threshold

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Cooperative Location-Sensing L1L1 L2L2 L3L3 L4L4 Host 4 CLS table: 1

Performance analysis  Simulation testbed 100*100 square units in size Node randomly placed The default number of nodes is 100  Compare with[18] Robust Positioning Algorithms for Distributed Ad-Hoc Wireless Sensor Networks, In Proc. of Usenix Annual Technical Conference, June 2002  Hop-Terrain  Hop-Terrain and with refinement

Performance analysis 10% hosts are landmarks

Performance analysis

Percentage of Landmarks

Conclusion  Devices running CLS can cooperate and share positioning information to improve their position estimations  CLS can work in both indoor and outdoor environments