Capturing the Shifting Shapes

Abstract

With the increasing availability of LCD displays and phone cameras in today's environment, screen-camera communication using dynamic barcode has emerged as a convenient infrastructure-free form to establish impromptu communication channel among mobile devices. Due to the short wavelengths and narrow beams of visible light, screen-camera communication is highly directional, low-interference and secure, which envisions a wide range of application scenarios. Conventional screen-camera communication systems encode data bits with color in dynamic barcodes, which suffers from the frame mixture problem caused by the rolling shutter effect of CMOS camera in high capturing rate. In this paper, we propose a novel design of dynamic barcode called ShiftCode that encodes data bits with shifting shape patterns, which provide a new way to expand the barcode capacity for screen-camera communications. ShiftCode adopts a pattern-based layout design to embed multiple data bits in a symbol representation. With such layout, it exploits a decoding mechanism to solve the frame mixture problem and achieves high frame capturing rate. It further intruduces a two-level reliability technique for intra-frame error correction and inter-frame redundancy, which reduces the overhead and delay of retransmission. The proposed ShiftCode is implemented on the Android platform, and extensive experiments show that it achieves at least two-fold improvement on goodput compared with the conventional screen-camera communication systems.