A New LED Response Model and its Application to Pre-Equalization in VLC Systems

With the growing interest in visible light communication (VLC), it is desired to transmit data at very high rates despite the LED's bandwidth becoming a bottleneck. The bandwidth of a white LED usually ranges between hundreds of kHz and a couple of MHz, limiting transmission rates dramatically in a VLC system. Successful design of an efficient equalizer for VLC systems heavily depends on the realistic modeling of LED's frequency response. In this letter, we first propose a new LED response model taking the parasitic effects appearing at higher frequencies into account. The proposed model provides better match with measurements of commercially available LEDs over a wide frequency range as compared to the existing models in the literature. Then, we design a digital equalizer in line with the proposed model and implement it as an offline digital system in Matlab. The designed equalizer yields an overall flat system response over a wide frequency range. As a demonstration, we present the measured eye diagrams and bit error rate performance results of the equalized VLC system with on-off keying modulation and demonstrate improvements in data rate in comparison to the LED bandwidth.