LED nonlinearity impact on Frequency Modulation signals over Visible Light Communication systems

In optical wireless communication systems using LED transmitters, the performance will be degraded due to the nonlinearity of LEDs. In this paper, analog Frequency Modulation over Visible Light Communication (FM-VLC) systems considering the influence of LED nonlinearity is investigated. The nonlinearity impact to carrier-to-noise ratio (CNR) and signal-to-noise ratio (SNR) is numerically analyzed and simulated. Moreover, an experiment that transmission of FM signal over VLC is setup with the results are given. For FM-VLC system based on nonlinear LED model, SNR is 5dB lower than that based on linear LED model, when modulation index n=1 which is the worst nonlinearity condition. Meanwhile, FM index is an important parameter that influence on the system performance. CNR changed little but SNR has a great improvement with FM index increasing. When FM index mf <; 0.5, transmission of Narrow-Band FM (NBFM) signals, SNR demodulated is lower than CNR. While FM index mf > 1, transmission of Wide-Band FM (WBFM) signals, SNR is higher than CNR, and low CNR can adopt high SNR. It is more suitable for transmission of WBFM signals than NBFM signals over VLC system.