## 1 Introduction
The above-mentioned descriptions are summarized as shown in Table 1. For your information, international standardization groups and European projects related to Li-Fi systems and flicker noise are as follows: Flicker mitigation solutions of PHYs in IEEE802.15.7 [18], Commercial Solutions for Classified (CSfC) for Li-Fi [19], and Enhance Lighting for the Internet of Things [20]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Technique** & & **Advantages and Weakness** & **Location** \\ \hline \multirow{4}{*}{\(\bullet\)} & & \(\bullet\) & Flicker noise elimination & \\  & & \(\bullet\) & Transmission rate reduction & \\  & Modulation format to avoid flicker noise & \(\bullet\) & High hardware complexity & \\  & & \(\bullet\) & A circuit or algorithm that recovers a specific modulated formatted signal & \\ \hline \multirow{2}{*}{\(\bullet\)} & LED driver circuit for flicker noise & \(\bullet\) & Flicker noise reduction & \\  & reduction & \(\bullet\) & High implementation cost & \\ \hline \multirow{4}{*}{\(\bullet\)} & & \(\bullet\) & Flicker noise reduction regardless of & \\  & & digital modulation format & \\ \cline{1-1}  & & DSP (digital signal processing) & \\ \cline{1-1}  & & implementation & \\ \cline{1-1}  & & Signals and noise with different & \\ \cline{1-1}  & & waveforms & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between the existing techniques and the proposed technique. In this paper, we propose a technique to reduce the imperceptible flicker noises generated in the LED driving circuit and in the process of digital modulation such as non-return-to-zero-on-off-keying (NRZ-OOK) in a Li-Fi system based on white LED. In the Li-Fi transmission system, two types of imperceptible flicker occur at a frequency of 120 Hz. First, when the LED driver circuit is being operated, the flicker noise of 120 Hz, which is twice the AC voltage frequency, is generated. Second, when the NRZ-OOK signal is modulated, the flicker may occur as the baseband signal components, including the 120 Hz frequency, are modulated. Furthermore, the light from the white LED is directly modulated at the same time by the flicker noise generated in the LED driver circuit and the NRZ-OOK signal. The imperceptible flicker noise corresponding to a frequency of 120 Hz shows the waveform of a sinusoidal signal. We propose the following two techniques to reduce the imperceptible flicker noise. Firstly, since the change in the derivative value between adjacent sampling points of the flicker noise signal with an analog waveform is much larger than that of the NRZ-OOK signal having a digital waveform, the sampling points value corresponding to the derivative value over the preset threshold value are extracted to reduce the flicker noise signal. However, in the VLC transmission link, various optical noises other than flicker noise are also generated during wireless optical transmission. In addition, since these noises also represent a random analog waveform, various optical noises, and the flicker noise can be reduced together. In this case, since sampling points corresponding to various optical noises are extracted, the flicker noise reduction effect may be lowered. Therefore, a sinusoidal weight function with a frequency of 120 Hz and a random Gaussian phase is proposed additionally in order to maximize the reduction of the flicker noise. We named the proposed technique pseudo-flicker weight functionalized derivative equalization. In our previous work, a technique to reduce the interference noises and shot noises, which are produced in other illuminations existing around the Li-Fi link, was proposed and then the experimental results were presented [21]. My previous work was focused on reducing the interference noise and shot noise produced by the electric circuits that generate various lights (fluorescent lamps, halogen lamps, etc.). In the proposed technique, we focused on reducing the flicker noise generated in the wireless Li-Fi transmitter including the electric circuit that drives white LED.