Thresholding Scheme Based on Boundary Pixels of Stripes for Visible Light Communication With Mobile-Phone Camera

In mobile-phone camera-based visible light communication (VLC) system, column matrix selection and threshold setting are very important steps for signal demodulation. As the blooming effect of complementary metal-oxide-semiconductor camera fluctuates grayscale values of pixels, thus causing a decrease in the accuracy of distinguishing data logic 0 and 1. Facing grayscale value fluctuation, using traditional polynomial fitting as the threshold to distinguish data logic 0 and 1, the achievable system performance is not very good. This limits applications of the VLC system. Therefore, advanced thresholding schemes are needed to increase the accuracy of distinguishing data logic 0 and 1, thereby improving the system performance. In this paper, we propose and experimentally demonstrate for the first time a thresholding scheme based on boundary pixels of stripes for improving the VLC system performance. First, we describe the process of boundary pixel position acquisition for the thresholding scheme in detail. Then, we analyze and discuss the selection of the optimum column matrix for signal demodulation. Finally, we demonstrate experiments to verify the feasibility of our proposed thresholding scheme. Experimental results show that our proposed thresholding scheme can achieve a good performance even when grayscale values fluctuate greatly. Compared with the conventional third-order polynomial fitting scheme, our proposed thresholding scheme has advantages in both of transmission distance and data rate. With aid of the optimum selected column matrix and our proposed thresholding scheme, a data rate of 4.5 Kb/s (2.5 Kb/s) is successfully achieved with the transmission distance of 50 cm (175 cm) under the 7% forward error correction limit (bit-error-rate = 3.8\times 10^{-3} ) for the VLC system with mobile-phone camera.