The designing of an indoor acoustic ranging system using the audible spread spectrum LFM (chirp) signal

This paper presents an audible spread spectrum (SS) acoustic ranging system for indoor applications. RF synchronization along with using wideband audible signal results in significant reduction in error and reduces the cost and complexity of the ranging hardware and removes the need for high sampling rates. The SS signal, which in this case, is a linear frequency modulated (LFM) pulse (chirp), emanates from a speaker and is received by a microphone. It is then correlated with a delayed copy of the same signal through a matched filter. Important issues of acoustic propagation, along with the impact of indoor reverberation on time of arrival (TOA) estimation are taken into account to use an appropriate LFM pulse. It is found that, an LFM pulse with 3 kHz bandwidth, center frequency of 2 kHz, and chirp rate of 60 Hz/ms would have good performance in range accuracy