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 smartphones 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° 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.