Near-ultrasound communication for TV's 2nd screen services

초록

In this paper, we propose a near-ultrasound chirp signal- based communication for the TV's 2nd screen services. While near-ultrasound (with under 20 kHz frequency) communi- cation has been developed for various applications recently, none of the previous work provides a perfect solution for 2nd screen services between TVs and smart devices. This is due mainly to the following real world challenges. The embed- ded signal in TV contents should be successfully received in a typical TV-watching environment by (i) delivering informa- tion at least at 15 bps with significantly low volume to avoid human perception, (ii) despite the presence of ambient noise, e.g., a tick, a snap, or a knock. To fulfill (i), we design chirp quaternary orthogonal keying (QOK) symbols. Especially, we aim to minimize inter-symbol interference (ISI) effects by symbol design in order to completely eliminate guard inter- vals. To resolve (ii), we propose the novel J-shape detection algorithms for both frame synchronization and carrier sens- ing. The proposed modem achieves almost zero frame error rate on a smartphone 2.7 m away from the TV even with minimal receive sound pressure level of 35 dBSPL, i.e., the noise level in a very quiet room. Moreover, throughout ex- periments and log analysis of 2nd screen service deployed in a nation-wide TV broadcasting system, J-shape detection al- gorithms are proven to achieve highly resilient performance for both frame synchronization and carrier sensing compared to previous schemes.