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Localization and Exploration for Intelligent Systems (LOPSI)

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Ultrasonic-based LPS

The LOPSI group uses ultrasonic technology for high accuracy positioning in small indoor areas. By measuring the time-of-flight (TOF) of ultrasonic signals propagating from several static beacons to a mobile node, its position can be computed by multilateration techniques, usually with an accuracy around 1 cm.

3D-Locus is an ultrasound-based LPS designed and built by the LOPSI group and used to accurately locate archaelogical finds and transmit their position to a computer. A thorough description of the system is found here. We use this prototype system as a platform in which we develop new transducers, signal processing techniques, and positioning algorithms.

3DLocus node
(Left) Concept design of the 3D-Locus system for archaelogical provenance sites: the workers carry a light pole equipped with ultrasonic emitters, and the set of beacon nodes is placed above their heads. (Right) An ultrasonic emitting/receiving node designed and built by LOPSI for the 3D-Locus system.

3DLocus prototype
Operative prototype of the 3D-Locus system in the LOPSI laboratory, showing the beacon network in the top part of the picture, and a robotic arm for system evaluation and calibration (click on the image for a larger picture).

These are some of the research topics on the LOPSI group in the field of ultrasound-based positioning systems
  • Development of new ultrasonic transducers based on flexible ferroelectret materials (EMFi), in order to improve the system's bandwidth and control the transducer's directivity.

   EMFi microphotography  EMFi transducer
(Left) Photography of the cross section of an EMFi film obtained with an electronic microscope at the CSIC. (Right) A hemi-spherical ultrasonic transducer built with EMFi film.

  • Modulation and codification of ultrasonic signals with Code Division Multiple Access processing (CDMA) techniques, for simultaneous operation with multiple transducers and precise ranging; in essence, replicating with ultrasonic technology the main features of the GPS positioning system.

   CDMA modulation  CDMA correlation
(Left) Ultrasonic signals are modulated in phase (BPSK) with digital orthogonal codes, and the correlation operator (right) is used to identify the signals coming from different transducers operating simultaneously.

  • Robust multilateration positioning in the presence of outliers in the time-of-flight measurements
  • Autocalibration methods to determine the position of the network of beacons

Last update: January 31st, 2011