This is a report of the team work we achieved during this evening.

The project “Localisation Indoors” is about localising a terminal (may it be a specific receptor or a cell phone) using ultrasonics and triangulation methods.

First we considered the datas we needed in order to apply a triangulation method. With knowing its distance to the different position-fixed terminal, a given item should be able to work out its exact position.

In order to avoid as many interferences as possible we figured out it would be easier to have the position-fixed terminals transmitting the ultrasonics and the user devices receiving those waves. To be able to work out the distance between a device and the transmitters, they all need a common clock. The NTP protocol (on ethernet for instance)  can synchronize the clocks with a precision of 1ms, which, concerning the speed of sound would result in a maximum of 30cm loss of precision (which remains acceptable).


We thought that existing terminals such of cell phones could be good receivers. In order to confirm our first thoughts, we send a 20kHz signal from a tablet and recorded on a PC. Thanks to the software Audacity, which provides filtering and specter analysis functions, we were able to detect a nice 20kHz peak.

Our next steps are :

  • finding the PSCC, to be able to organize our work
  • think more the architecture of the tranceivers
  • check we can apply a triangulation method in simple conditions
  • think about the propagation problem ultrasonics may encounter


Please feel free to leave any comment concerning our choices, any suggestions are welcomed as well !

Jean-Baptiste Lescher

2 comments to D-73

  • nitruk

    I’m not sure I understand you well : you think cell phones could be good receivers, and your experience testifies that the given tablet is a good emitter ?

  • jb

    Well, you are right, there is a twist here.
    First of all it was just a primary experiment and we were glad to see the technology could work under very specific conditions.

    The goal of the experiment should have been named : “can microphones used in common devices (such as computers or cell phones) record a 20kHz sound”. The microphone tested was on Alexis computer for conveniency. Indeed a computer thanks to Audacity, provided the basic tools for a good overview of the recording and specter analysis.

    Experiences testing the reception quality of a cell phone should come soon.
    A positive result would be very handy, otherwise we shall think of building our own receiver.

    Please feel free to comment !
    Has this answered your question ?