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Details of the Real Time Linux Foundation Working Group Project

OSADL Project: Real Time Linux Workshops

Real Time Linux Foundation Workshops since 1999

Real Time Linux Workshops

1999 - 2000 - 2001 - 2002 - 2003 - 2004 - 2005 - 2006 - 2007 - 2008 - 2009 - 2010

Eighth Real-Time Linux Workshop on October 12 to 15, 2006, in Lanzhou, Gansu, P.R.China

GNU/Linux Based TDOA Localization Using COTS Hardware

Georg Schiesser
OpenTech EDV-Research GmbH OPENTECH
Lichtenstein Str 31, 2130 Mistelbach, AUSTRIA
e0307201ªstudent.tuwien.ac.at

The goal of this project is to determine the position of a sound source using an array of four microphones, a good quality audio card and a GNU/Linux based PC. The microphones are located at exactly known positions somewhere in the room. Time-Difference-Of-Arrival (TDOA) localization is based on the fact that the sound signal is received at the microphones with relative time-differences, depending on the distance between microphone and sound source and the speed of sound in air (c $\approx$ 343 m/s). At present either a frequency generator or a test-signal are used as the sound source. Later it will be possible to use other sound sources like clapping hands but recent measurements showed that this is difficult because of nonlinear recording effects like echo and distortion. Up to now the audio signals are recorded using ALSA. In general every tool can be used to record audio. One of the project's goals is to use the real-time audio toolkit RAT in a later version to guarantee minimal latencies in the recording interface. The calculation of the TDOA values between the four audio streams is based on an iterative cross-correlation algorithm optimized for low latencies. Every channel is compared with every other channel at different time lags ranging from -WINDOW to +WINDOW. The maximum value indicates the time difference at which two channels are correlated. Traditional algorithms are based on FFT or other transformations, but these techniques cannot be used if the TDOA values must be updated after every sample to keep the latencies at the minimum. In general TDOA localization can be thought of calculating the intersection of multiple hyperboloids. The equation system is too complex to be solved exactly. So the position of the sound source is approximated using Newton's method of multidimensional-root-finding. The algorithm is based on the GNU Scientific Library (GSL).

 

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