# Spatial Multiplexing Holography for Multi-User Visible Light Communication
## 5 Experimental Results  
### Experimental Results for Power Allocation  
Within VLC systems, we consider three distinct types of users: VR glasses users, PC users, and smartphone users, each with unique video quality requirements. VR glasses users typically engage in viewing 4K virtual reality movies, necessitating the highest data rate. Conversely, PC users generally require sufficient bandwidth to watch 1080p videos, while smartphone users often consume content at lower resolutions, such as 720p shorts, which demands a comparatively lower data rate. To quantify these requirements, we calculated the necessary data rates for each video resolution category. To examine the impact of received optical power (ROP) on these data rates, we employed neutral-density filters (NDs) to systematically vary the ROP. The resulting relationship between data rate and ROP is illustrated in Figure 8a. This analysis aids in determining the optimal power allocation strategy, facilitating the creation of SMH tailored to the diverse needs of VR glasses, PC, and smartphone users. As depicted in Figure 8a, distinct user requirements necessitate varying data rates for satisfactory video quality. For VR glasses users aiming to watch 4K videos at 40 FPS, a minimum data rate of 2.47 Gbps is required, with a corresponding ROP of 2 mW. In contrast, PC users viewing 1080p videos at 75 FPS with 10 bit real color require a lower data rate of 1.45 Gbps, associated with an ROP of 0.7 mW. Meanwhile, smartphone users,  
Figure 8: Experimental results for power allocation. (**a**) Data rate curve with ROP; (**b**) One frame of 4K video received under MPH and SMH; (**c**) BER of each row in the first frame; (**d**) Mean BER of each second of the video; (**e**) Working point test for User 1; (**f**) Working point test for User 2; (**g**) Working point test for User 3.  
typically watching 720p shorts at 60 FPS, necessitate an even more modest data rate of 0.41 Gbps, with a corresponding ROP of 0.3 mW. From these specifications, we established the target power allocation ratio as 0.15, 0.35, and 1 for smartphone, PC, and VR glasses users, respectively. In our experimental setup, we employed ND to adjust the optical power received by the user positioned at 0.8 m--specifically, the VR glasses user--to meet the required ROP. Subsequently, we conducted experiments to adjust the power for the other two user types, aligning with their respective data rate requirements. Figure 8b illustrates a single frame of a 4K video as received by the VR glasses user, comparing the results under MPH and SMH methodologies. Notably, the MPH lacks effective power allocation capabilities. Consequently, VR glasses users, positioned at the most distant plates in the forward transmission space, typically receive the least power. This insufficiency hinders their ability to achieve the required data rate for streaming 4K video, leading to a high BER and, subsequently, a diminished viewing experience. In contrast, the SMH method significantly enhances the ROP for the VR glasses user by strategically reducing the ROP allocated to the other two user types. This optimization allows the VR glasses user to view 4K videos seamlessly, without any bit errors after post-FEC. Figure 8c demonstrates the BER of each row when reconstructing the first frame of the video. It is evident that MPH has a high BER, which remains above the threshold even after post-FEC correction. In contrast, SMH consistently maintains the BER below the threshold. Figure 8d depicts the mean BER of each second of the video, showing significant fluctuations in BER with MPH methods. Conversely, SMH remains stable and consistently below the threshold. Figure 8e-g present the data rate curves for different users as a function of the waveform voltage (peak-to-peak voltage, Vpp) of the signals. All users achieved their highest data rates at a Vpp of 200 mV.