Ultrasound Communication Using the Nonlinearity Effect of Microphone Circuits in Smart Devices

Acoustic communication has become a research focus without requiring extra hardware and facilitates numerous near-field applications such as mobile payment. To communicate, existing researchers either use audible frequency band or inaudible one. The former gains a high throughput but endures being audible, which can be annoying to users. The latter, although inaudible, falls short in throughput due to the available (near) ultrasonic bandwidth. In this paper, we achieve both high speed and inaudibility for acoustic communication by utilizing the nonlinearity effect on microphones. We theoretically prove the maximum throughput of inaudible acoustic communication by modulating audible signal onto ultrasonic band. Then, we design and implement UltraComm, which utilizes a specially-designed OFDM scheme. The scheme takes into account the characteristics of the nonlinear speaker-to-microphone channel, aiming to mitigate the effects of signal distortion. We evaluate UltraComm on different mobile devices and achieve throughput as high as 16.24 kbps.