NECAS: Near field communication system for smartphones based on visible light

A novel near field communication system for s-martphones based on visible light (NECAS) is presented in this paper. NECAS encodes information using combinations of different colors (red, green and blue) and their intensity levels of a smartphone screen, while the receiver captures the light signal via color sensors. In our scheme, a smartphone screen is segmented into four sub-blocks, and each of them can be used to encode information independently. NECAS can be used in a range of Near Field Communication applications such as contactless payments, electronic ticket checking and device paring. We design the color encoding scheme by experimentally profiling the interference of three color channels and the refresh rate of smartphones. We implement a joint decoding algorithm to deal with the significant interference among color channels. With a feedback channel, the retransmission scheme is adopted to improve communication reliability, and the system can dynamically adjust the number of combinations of different colors and intensity levels to fit the communication environment. Our design is validated via extensive experiments using a hardware implementation on Android smartphones and an Arduino platform.