Messages Behind The Sound: Real-Time Hidden Acoustic Signal Capture With Smartphones

With the ever-increasing use of smart devices, recent research endeavors have led to unobtrusive screen-camera communication channel designs, which allow simultaneous screen viewing and hidden screen-camera communication. Such practices, albeit innovative and effective, require well controlled alignment of camera and screen and obstacle-free access.In this paper, we develop Dolphin, a novel form of real-time acoustics-based dual-channel communication, which uses a speaker and the microphones on off-the-shelf smart phones to achieve concurrent audible and hidden communication. By leveraging masking effects of the human auditory system and readily available audio signals in our daily lives, Dolphin ensures real-time unobtrusive speaker microphone data communication without affecting the primary audio-hearing experience for human users, while, at the same time, it overcomes the main limitations of existing screen-camera links. Our Dolphin prototype, built using off-the-shelf smartphones, realizes real-time hidden communication, supports up to 8-meter signal capture distance and +/- 90 degrees listening angle and achieves decoding rate above 80% without error correction. Further, it achieves average data rates of up to 500bps while keeping the decoding rate above 95% within a distance of 1m.