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)


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.


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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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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