CCT-adaptive dual-branch pre-equalization for pc-LED based visible light communication

Phosphor-converted LEDs (pc-LEDs) are the dominant source for general illumination. However, their limited modulation bandwidth poses a significant challenge for Visible Light Communication (VLC). Existing research has proposed blue-yellow light shunt systems and frequency response models that incorporate Correlated Color Temperature (CCT) and phosphor delay. Nonetheless, they lack targeted equalization schemes. To address this, in this paper, a dual-branch pre-equalization scheme is proposed to match the physical characteristics of pc-LEDs. The frequency domain is divided into high and low segments bounded by a frequency-division point, and their frequency responses are reshaped to design an equalizer accordingly. The two branches compensate for the yellow light response dominated by low frequencies and the blue light response dominated by high frequencies, respectively. Moreover, a prediction formula is derived to intelligently determine the optimal frequency-division point based on CCT and phosphor delay. Simulation results verify the accuracy of the formula that yields a prediction error of less than 0.05 MHz. This scheme can effectively improve the communication performance of the system. In a 2.5-meter Line-of-Sight (LOS) link, the data rate reaches 130 Mbps at 3000 K, 120 Mbps and 115 Mbps at 4000 K and 5000 K respectively. Even with the consideration of phosphor delay, the data rate remains above 115 Mbps.