Abstract
The effective communications range for aerial acoustic communication in indoor environment is a critical challenge for applications on smartphones. An inaudible acoustic communication system on Android phones that breaks the range limit is proposed in this paper, owing to an innovative design of the receiver by considering the time–frequency features of the received signals, using a fractional Fourier transform and 2-D mask filter to denoise the signals, and a hard detection and a soft detection approach to detect the symbols so as to tackle the severe multipath and Doppler effects in large indoor environments. Onsite test results show that an error-free communication distance of 70 m can be achieved at 20 bps, and the estimated maximum communication range could reach at least 85 m.