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SmartMoveX on a Graph - An Inexpensive Active Badge Tracker

  • John Krumm
  • Lyndsay Williams
  • Greg Smith
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 2498)

Abstract

Measuring the locations of people in a building is an important part of ubiquitous computing. We present new hardware and software for this purpose. The hardware, called SmartMoveX, is an active badge system in which a small radio transmitter is attached to the person being tracked. Receivers placed in the building’s existing offices, connected to existing PCs, transmit signal strength readings to a central PC using the building’s existing computer network. Combined with the low cost of the hardware, using the existing network makes this active badge system much less expensive than many others. To compute locations based on signal strength, we gathered signal strength readings from predefined location nodes in the building. We defined a graph on these nodes, which allowed us to enforce constraints on computed movements between nodes (e.g. cannot pass through walls) and to probabilistically enforce our expectations on transitions between connected nodes. Modeling the data with a hidden Markov model, we used the Viterbi algorithm to compute optimal paths based on signal strengths over the node graph. The average location error was 3.05 meters, which compared favorably to a simple nearest neighbor algorithm’s average location error of 4.57 meters.

Keywords

Hide Markov Model Signal Strength Ubiquitous Computing Viterbi Algorithm Neighbor Algorithm 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    Hightower, J., G. Borriello, and R. Want, SpotOn: An Indoor 3D Location Sensing Technology Based on RF Signal Strength, UW-CSE 2000-02-02, University of Washington, 2000.Google Scholar
  2. 2.
    Hightower, J., et al., Design and Calibration of the SpotOn Ad-Hoc Location Sensing System, http://www.cs.washington.edu/homes/jeffro/pubs/hightower2001design/hightower2001design.pdf
  3. 3.
    Seidel, S.Y. and T.S. Rapport, 914 MHz Path Loss Prediction Model for Indoor Wireless Communications in Multifloored Buildings. IEEE Transactions on Antennas and Propagation, 1992. 40(2): p. 207–217.CrossRefGoogle Scholar
  4. 4.
    Bahl, P. and V.N. Padmanabhan. RADAR: An In-Building RF-Based Location and Tracking System in IEEE INFOCOM 2000. 2000. Tel-Aviv, Israel.Google Scholar
  5. 5.
    Rabiner, L.R., A Tutorial on Hidden Markov Models and Selected Applications in Speech Recognition. Proceedings of the IEEE, 1989. 77(2): p. 257–285.CrossRefGoogle Scholar
  6. 6.
    Want, R., et al., The Active Badge Location System. ACM Transactions on Information Systems, 1992. 10(1): p. 91–102.CrossRefGoogle Scholar
  7. 7.
    Hightower, J. and G. Borriello, Location Systems for Ubiquitous Computing. Computer, 2001. 34(8): p. 57–66.CrossRefGoogle Scholar
  8. 8.
    Proximity Acitivated Identification, http://www.pcprox.com/Support/AIRID/airid.html.
  9. 9.
    Spratt, M., An Overview of Positioning by Diffusion, HPL-2001-207, HP Laboratories Bristol, 2001.Google Scholar
  10. 10.
    Priyantha, N.B., A. Chakraborty, and H. Balakrishnan. The Cricket Location-Support System. in 6th ACM International Conference on Mobile Computing and Networking. 2000. Boston: ACM Press.Google Scholar
  11. 11.
    Randell, C. and H. Muller. Low Cost Indoor Positioning System. in Ubicomp 2001. 2001. Atlanta, GA, USA: Springer.Google Scholar
  12. 12.
    Harter, A., et al. The Anatomy of a Context-Aware Application. in 5th Annual ACM/IEEE International Conference on Mobile Computing and Networking. 1999. Seattle, WA: ACM Press.Google Scholar
  13. 13.
    Castro, P., et al. A Probabilistic Room Location Service for Wireless Networked Environments, in Ubicomp 2001. 2001. Atlanta, GA, USA: Springer.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2002

Authors and Affiliations

  • John Krumm
    • 1
  • Lyndsay Williams
    • 2
  • Greg Smith
    • 1
  1. 1.Microsoft ResearchRedmondUSA
  2. 2.Microsoft ResearchCambridgeUK

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