# Spatial Multiplexing Holography for Multi-User Visible Light Communication
## 5 Experimental Results
### Experimental Results for Power Coverage  
In the power coverage experiment, the diameters for the power coverage areas of the users were set at 2 mm, 4 mm, and 6 mm, respectively, corresponding to their spatial locations. We assessed the variation in power as each receiver moved along the x-axis and y-axis. Due to the circular nature of the light spots, we averaged the values from the negative and positive axes for both x and y, yielding a comprehensive measure of the X or Y (abbreviated as X/Y) plane's offset values, as depicted in Figure 9a-c. In Figure 9a, we observe that within User 1's coverage area, the optical power loss experienced under the SMH method is only 0.81 dB. In contrast, under the MF method, this loss significantly increases to 10.21 dB. Consequently, the improvement from MF to SMH at the edge of the target coverage area is notable, registering at 8.4 dB. Similarly, Figure 9b reveals that within User 2's designated coverage area, the optical power loss under SMH is minimized to 1.14 dB, compared to a much larger loss of 15.66 dB under the MF method. This results in an enhancement from MF to SMH at the boundary of the coverage area by 11.6 dB. Lastly, Figure 9c shows that for User 3's coverage area, the power loss under SMH is recorded at 1.34 dB, significantly less than the 12.39 dB loss under the MF method. The improvement from MF to SMH at the coverage area's edge is, therefore, 8.9 dB. In Figure 9d, we define the power coverage area as the region where the power loss is less than 1 dB compared to the central power. For User 1, the power coverage achieved under the SMH method was 113.6% of the target region, significantly surpassing the mere 9.8% achieved under the MF method. Similarly, User 2 experienced an 84.8% coverage with SMH compared to only 3.6% with MF. Meanwhile, User 3's coverage area was 69.3% under SMH, which is substantially higher than the 6.98% provided by MF. These results clearly demonstrate that the SMH method significantly outperforms the MF method in terms of maintaining adequate power coverage. This indicates the superior performance of SMH in ensuring extensive and uniform power distribution across different users within the targeted regions.  
Figure 9: Experimental results for power coverage. (**a**) User 1’s ROP trend with XoY offset; (**b**) User 2’s ROP trend with XoY offset; (**c**) User 3’s ROP trend with XoY offset; (**d**) Coverage area diameter of 3 users under MF and SMH; (**e**) Data rate trend with XoY offset of three users; (**f**) CCD recording at User 1’s plate under different methods; (**g**) CCD recording at User 2’s plate under different methods; (**h**) CCD recording at User 3’s plate under different methods; (**i**) MSE and SSIM of recordings under different methods.  
Figure 9e displays the variations in data rate relative to the central data rate as a function of the X/Y offset. This trend mirrors the pattern observed for ROP in relation to the X/Y displacement. Under the MF method, all users exhibit a pronounced decline in data rate immediately beyond the central area. In contrast, for users under the SMH method, the rate of data loss aligns more closely with the predefined coverage area, indicating a more uniform distribution of data rates within the targeted region. Figure 9f,g feature images captured by a CCD at the users' respective plates. The size of the light spot closely matches the intended target size under SMH, whereas the light spot is much smaller than the target size under MF methods. Specifically, using Mean Square Error (MSE) and Structural Similarity (SSIM) to evaluate the imaging results, SMH demonstrates better stability in both metrics, while MF exhibits significant fluctuations. These images further illustrate that the smaller the spot, the greater its brightness, indicative of the ROP's intensity.