Visible light communication is one of the key technologies for intelligent transport systems (ITS). However, current visible light communication systems require high-cost devices, such as high-speed image sensors, to support their high transmission rates. In this paper, we designed a communication system with combination of a low-speed commercial image sensor and a polygon mirror — namely, a fast-blinking light signal is scanned by the polygon mirror and captured as a residual image on the low-speed image sensor — to achieve visible light communication on existing mobile devices with high transmission rates. We also analyzed some required conditions, such as the relationship between the exposure time of the image sensor and the optimal resolution, and conducted experiments for performance evaluation. As a result, we found that the proposed system could achieve a data rate of 120bps, 10 times faster than that of the existing scheme when we compare them using the same image sensor. We also found that the proposed system can achieve a practical bit error rate in a low-noise environment.

In this paper, we propose a secure near-field communication (NFC) for smartphones by combining acoustic and vibrational communication. In our hybrid system, a transmitter transmits an encrypted message and encryption key from a loudspeaker and vibration motor, respectively. While the sound emitted from the loudspeaker propagates through the air, the vibration emitted by the vibration motor propagates through the body of smartphones. Hence, only receivers touching the transmitter can receive both the encrypted message and the key, resulting in secure communication. We designed a software modulator and demodulator suitable for the vibrational communication by using return-to-zero (RZ) code. Then we established a hybrid communication system by combining acoustic and vibrational communication modems, and evaluated its performance in experiments. The results indicate that our hybrid system achieved a secure (among physically contacted devices) and fast (800kbps) NFC for smartphones.