Fine-grained acoustic positioning

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.

An ultrasonic emitting/receiving node designed and built by LOPSI for the 3D-Locus system.
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.
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.
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.
Ultrasonic signals are modulated in phase (BPSK) with digital orthogonal codes
  • 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