Interference Cancellation Method For Visible Light Communication System

With the rapid development of LED(Light Emitting Diode) technology and the increasing demand of high-speed wireless communication, visible light communication technology gradually develops. As a new type of wireless communication means, it obtains the wide attention of the domestic and foreign research institutions and scholars, providing a flexible solution for wireless broadband access and effectively alleviating the increasingly crowed spectrum resources issues in wireless communication. Visible light communication technology is also applied in intelligent transportation system. With LEDs as traffic light, visible light communication system provides a new solution for ITS to solve communication.The paper is based on visible light communication for road and vehicle with LED array. The light signal emitted by LED array is intensity modulated, the receiver captures the transmitting LED images by high-speed camera and demodulates original information, completing the visible light communication. Drawback particular to the system is inter-pixel interference(IPI). Due to diffusion of LED and finite pixel size of image sensor, the LED affects not only the actual corresponding pixel but also its surrounding pixels. We call this phenomenon as “inter-pixel interference(IPI)” and it causes degradation in error rate performance. In this paper, we study mainly methods to eliminate the effect of IPI.1. The paper proposes two frequency domain equalization algorithms to eliminate IPI: zero-forcing frequency domain equalization and minimum mean square error frequency domain equalization. And the bit error rate(BER) performance in white Gaussian noise channel is simulated. It can be seen that these two frequency domain equalization algorithms can both improve the BER performance in a serious IPI. And by comparing these two algorithms, it can be seen that at low SNR, MMSE equalization is worse than zero-forcing equalization in performance and at high SNR, MMSE equalization is better than zero-forcing equalization in performance.2. The paper proposes selecting equalization algorithm. No equalization is better than equalization in performance in a little IPI. For this situation, the paper presents a selecting equalization algorithm. Selecting equalization can choose whether or not to equalize. BER performance is simulated in the absence and presence of the background light. We come to the conclusion that equalization can improve the BER performance, resisting background light noise to a certain degree.By simulation and experiment, it can be verified that equalization algorithm can reduce inter-pixel interference and improve the BER performance of the system.