# Laser-Based Mobile Visible Light Communication System
## 2 Experiment Setup
To facilitate communication measurements during mobility, we designed and customized a set of electric rails and a control system specifically for mobile VLC, as depicted in Figure 4.  
Figure 3: Optical power distribution of the light source after passing through a blue light filter at 1 m and 2 m.  
Figure 2: **(a)** Spectrum of the laser-based white light we employ in this work. **(b)** Chromaticity coordinates of the laser-based white light. The emission peak is located at 452 nm, the coordinates are x = 0.2969, y = 0.2888. The track was 1.2 m in length, with a safety margin of 0.2 m at each end, resulting in a general movement range of 0.8 m along the center of the track, corresponding to coordinates of 0-0.8 m. The rotation of the motor drove the moving platform to slide on the track via a synchronous belt. The pitch of the synchronous belt was 162 mm per revolution, meaning that when the speed was set to 1 S/r, the mobile platform moved forward 162 mm in one second. A control box was positioned on the left side of the track, enabling the movement of the platform at different predetermined speeds. The VLC experimental system, including the communication equipment, is depicted in Figure 5. In Figure 5a, the perspective is from the transmitting end at one meter. As our light source provided broad coverage, it can be observed from the figure that the entire track was within the coverage area of the light spot. Therefore, theoretically, the receiving end could transmit via the visible light link when moving along the track. The receiver, an SiPM, was placed on the moving platform to achieve signal transmission during motion, as illustrated in Figure 5b. The setup of the mobile VLC system is shown in Figure 5c. The system's transmitter was located on the left, mounted on a movable cart to change the distance between the transmitter and receiver, thereby allowing the study of mobile communication performance over varying distances. On the right side was the system's receiver, with the mobile communication track placed on a desktop with the receiving detector on it. The OOK signal was generated by an arbitrary waveform generator (Keysight M8190A, Santa Rosa, CA, USA), and its amplitude was adjusted through an amplifier (Mini-Circuits ZHL-5W-1+, New York, NY, USA) and an attenuator (Alf Communications Key-Press Attenuator kT2.5-30/1S-2S, Shenzhen, China). Subsequently, the signal was coupled with a direct current to drive the light source to emit light, using a bias tee (Mini-Circuits ZFBT-282-1.5A+, New York, NY, USA). After traversing the mobile-free space channel, the SiPM collected the optical signal and converted it into an electrical signal, which was then forwarded to an oscilloscope for sampling, demodulation, and BER calculation. It is noteworthy that we utilized a lens-free receiver, which possesses considerable advantages in practical applications. The absence of lenses in the design simplifies the optical architecture, reducing the complexity and potentially lowering the cost of the system. Furthermore, this configuration allows for a more compact and lightweight design, making it more suitable for integration into mobile devices and applications where space and weight are critical constraints. Figure 4: Mobile track and controlling equipment.