Short range, >100Kbits/s, visible light communication protocol design for high-gamma smartphones

High gamma smartphones based on Android operating system support the development of third-party applications. This kind of devices include subsystems such as sensors and actuators which can be used for diverse purposes. One example is the implementation of short range visible light communication (VLC) channels where the built-in light-emitting diode (LED) is the transmitter, and the complementary metal-oxide semiconductor (CMOS) camera works as the receiver. A major challenge for this communication channel is the modulation bandwidth of the light source which is limited to a few MHz, and the availability of a line-of-sight. The camera shutter is limited to a few frames per second (30 or 60 fps) for a few bits per second transmission, but the Rolling Shutter effect could allow the enhancement of the bit rate. In this work, we propose a VLC protocol design for the use of the built-in camera and the flash LED in order to implement a short range VLC channel, for high gamma mobile-to-mobile devices based on Android. The design is based on On-Off Keying (OOK) modulation for initially transmitting a few bits. Based on the rolling shutter effect in the CMOS image sensor, bright and dark fringes can be observed within each received frame, and the data can then be retrieved. Furthermore, two thresholding schemes for high fluctuation and large extinction ratio (ER) variations in each frame, are explored. Full protocol design and short range (5 cm), >100 kbits/s, VLC demonstration and image processing results will be included in the presentation.