## 3 Experimental Setup  
### Li-Fi Transmission Link Testbed Based on Sparse Coded Mask Model  
Figure 2 illustrates the optical wireless Li-Fi transmission link implemented for the experimental verification of the proposed technique. The dotted box represents the offline processing conducted using MATLAB(r) 2023a interfaced with Python 3.13.2. As shown in the dotted box on the left, the DMT signal encoded by QPSK symbols is designed to have 512 subcarriers, allocated from DC up to 10 MHz. To eliminate spike noise occurring near DC, zero-padding was applied to the first 20 subcarriers. A cyclic prefix (CP) of length 16 was added to maintain orthogonality during the optical wireless transmission and then the parallel-processed DMT signal was converted to serial form. Each DMT symbol consists of 528 samples, and a total of four DMT symbols were transmitted, resulting in 2112 samples. To ensure clear separation between consecutive DMT symbols, 40 zero-padding samples were inserted four times, leading to a total of 160 zero-padding samples. Consequently, the final DMT signal length is 2272 samples, which is not an integer multiple of 528 due to the addition of zero-padding. This design was chosen in order to enhance symbol boundary clarity and effectively minimize inter-symbol interference. Waveforms measured from (A) to (D) point are shown at the bottom of Figure 2. Here, the masking ratio was 75%, which means that 75% of the entire DMT signal waveform was removed, and only 25% was retained for transmission. This DMT signal is evenly divided into 16 patches, with each patch having a length of 142 samples (=2272/16). These 16 patches are then treated as 16-DMT waveform images and processed through a 1-dimensional convolutional filter (embedding dimension: 1024, kernel size: 16, stride: 16) to perform patch embedding. As a result, 142-embedded patches, each with a dimension of 1 \(\times\) 1024, are obtained. Next, random masking is applied to compress the DMT signal. In case of 75% random masking, the total length of unmasked patches is 568 (=142 \(\times\) 16 \(\times\) 0.25). Here, its batch size is set to 32. We set the learning rate to 0.00025. The remaining unmasked patches, together with the positional encoding patches, were combined to generate the latent representation of the DMT signal. It was loaded into an arbitrary waveform generator (AWG) sampled at 40 MS/s. The signal output from the AWG was amplified by a low-noise amplifier (LNA) and then biased with a DC power supply using a bias-tee. The optical signal emitted from the white LED was directly modulated by the biased AWG output signal and transmitted over a 1-m free-space optical link to an avalanche photodiode (APD). The light intensity measured at the APD was 300 lux. After optical detection at the APD, the received signal waveform corresponding to the latent representation of DMT signal was captured and then stored by a real-time oscilloscope (MSO 71604C, Tektronix, Beaverton, OR, USA) sampled at 120 MS/s. Since the captured signal consisted of transmitted DMT patches and positional encoding patches, the positions of the transmitted patches were determined using the positional encoding patches to reconstruct the masked patches. Subsequently, the masked patches are reconstructed through an MAE-based decoding process, which is performed in reverse order of the encoding process, extracting the feature points. Using the reconstructed ones with the transmitted patches, the DMT signal wave  
Figure 2: Experimental setup for Li-Fi-based optical wireless transmission. Top: Photographs of the physical experiment showing the transmitter (AWG, LED, LNA), receiver (APD, oscilloscope), and optical alignment. Insets include close-up views of the LED and APD modules. Bottom: Measured time-domain waveforms at key stages (**A**–**D**), with zoomed-in views (**A**-**1,**D**-**1**) highlighting temporal characteristics before and after reconstruction. form was recovered and then the CP was removed.