A camera-based mobile data channel: capacity and analysis

In this paper we propose a novel application, color Video Code (V-Code) and analyze its data transmission capacity through camera-based mobile data channels. Users can use the camera on a mobile device (PDA or camera phone) as a passive and pervasive data channel to download data encoded as a sequence of color visual patterns. The color V-Code is animated on a display, acquired by the camera and decoded by the pre-embedded software in the mobile device. One interesting question is what is the data transmission capacity it can achieve, theoretically and practically. To answer this question we build a camera channel model to measure color degradation using information theory and show that the capacity of the camera channel can be improved with the optimized color selection through color calibration. After initialization color models are learned automatically as downloading proceeds. We address the problem of precise registration, and implemented a fast perspective correction method to accelerate the decoder in real-time on a resource constrained device. With the optimized color set and efficient implementation we achieve a transmission bit rate of 15.4kbps on a common iMate Jamin phone (200MHz CPU). This speed is faster than the average GPRS bit rate (12kbps).