## 4 Experimental Results
Another important point is that when the bias voltage is 4V, about 1.5-dB SNR gain can be obtained using the proposed technique based on the 1 st general forward error correction (GFEC) BER threshold. In other words, it is possible to transmit the NRZ-OOK signal if its SNR is 17 dB in the case of using the proposed technique. However, the SNR of 18.5 dB or more is required to transmit the NRZ-OOK signal when the proposed technique is not utilized. Additionally, as mentioned in Figure 3, the SNR corresponding to 10% flicker modulation at 4 V biased voltage was 20 dB. In this case, the BER without using the proposed method was 3.5 \(\times\) 10\({}^{-5}\) as shown in Figure 4. Therefore, the BER (3.5 \(\times\) 10\({}^{-5}\)) corresponding to 10% flicker modulation is obtained using the proposed technique even when the SNR of the input NRZ-OOK signal is set to 18 dB, not 20 dB. This result tells us that optical wireless transmission is possible even in an illuminance environment where the flicker modulation is reduced from 10% to 7%. It is necessary to verify the effect of the pseudo-flicker weight function mentioned in Equation (6) in order to remove the flicker noise. So, we compared the performance between the conventional total variation (TV) technique and the proposed technique. The technique proposed by [PERSON] was employed as the conventional TV [24]. Figure 5 shows the measured BERs for the proposed technique and the conventional TV, respectively. The inserted eye patterns in Figure 5 show the one in the case of not using the proposed technique, the one in the case of using the conventional TV, and the one in the case of using the proposed technique from the top in order. The signal waveform located on the right side of Figure 5 shows the NRZ-OOK signal waveforms in the case of using  
Figure 4: BER of NRZ-OOK signal vs. input SNR. the general TV technique and the proposed technique. In the case of using the general TV, the high-frequency noises were reduced (refer to the enlarged waveform near 6 ms). However, it was found that the 120 Hz flicker noise was maintained because the overall signal waveform was tilted. In the case of using the proposed technique, it could be seen that the NRZ-OOK signal waveform was uniformly recovered without inclination due to the pseudo-flicker weight function. In addition, as shown in Figure 5, an SNR gain of about 1.5 dB was obtained using the proposed technique compared to the conventional TV at the 1 st GFEC BER threshold. Figure 6 shows the measured BERs while increasing the received optical power from 200 Lux to 700 Lux. At this time, the biased voltage was set to 4 V and the input SNR was set to 20 dB. Filled squares show the BER when the proposed technique is not applied, and filled red circles show the BER when the proposed technique is applied. As shown in Figure 6, it was found that the BER corresponding to the first-generation GFEC threshold can be obtained even if the received light intensity is reduced by 50 Lux using the proposed technique. Reducing the received light intensity means less likely to create an illuminating environment with flicker noise. The BER floor was also observed when the received light intensity exceeded 500 Lux. This is because the signal-to-noise ratio of the recovered NRZ-OOK signal does not increase any more even when the received light intensity increases. Figure 5: BER comparison between the proposed technique and conventional TV. Figure 6: BER of NRZ–OOK signal vs. received light intensity.