Abstract
Both signal choice and signal processing for the time-of-flight identification are key factors for accuracy of measurement using an audio frequency region which is suitable for long distance acoustic paths. In this report, both factors have been studied on the view points of outdoor environment. At first, matched filter with pre-whitener and complex absolute detection has been derived for the optimal signal processor to be free from non-linear phase shift. Then, M-sequence Phase Reversal Keying has been concluded as the best strategy to cope with varying noise spectrum. Finally, comparison with the previous technique shall be introduced.
