## 3 Adaptive Field-of-View Visible Light Communication: Concept and Prototype Development
### Presentation of the Experimental Testing Procedure  
This section presents the method of experimental testing, with the aim of determining the benefits of the proposed concepts by comparison with a similar prototype whose adaptive FoV characteristic was disabled. The testing procedure involved the VLC transmitter described in Section 3.1, placed at approximately 50 m from the two VLC receivers, whose basic characteristics are detailed in Section 3.2. It should be clarified that the two VLC receivers had the same hardware and software structures, and were calibrated to have the same settings (i.e., optical components, gain, filtering options, etc.), with the only difference being the adaptive FoV characteristics of one of the two VLC receivers. Additionally, it should be emphasized that a relatively long communication range was envisioned by these tests in order to take the link close to its limit. In this way, the impact of the adaptive FoV was more obvious. Otherwise, at shorter communication ranges, the higher SNR could be enough to keep the link active or to be less influenced by the sunlight.  
The experimental tests were conducted over an entire day, from sunrise to sunset, in order to evaluate the variable sun's impact on the vehicular VLC during the day. From this perspective, early in the morning and late in the afternoon, the sun's intensity is less powerful, but the light incidence angle is lower, which has a more negative impact on the VLC receiver's performance when it is receiving direct light exposure. In such circumstances when the VLC receiver is facing the sun, a narrow FoV could be more suitable. On the other hand, during midday, the sun's intensity is significantly higher, reaching values that can rise up to 100,000 \(\mu\)W/cm\({}^{2}\). Additionally, the clouds can significantly influence the sun's impact on the VLC receiver. As the sun's impact on the VLC receiver depends on so many aspects, it is obvious that a fixed FoV receiver is less adequate for vehicular applications.  
The schematic of the experimental testing setup is illustrated in Figure 3, exemplifying the envisioned testing scenario and the equipment layout. The projected setup assumed a vehicle approaching a traffic light. Nevertheless, depending on the moment of the day, the sun's intensity and location, and the weather conditions (e.g., absence of clouds), the VLC receiver could experience variable optical interference levels and a variable SNR. Under certain conditions, the optical interference could be so strong that the communication link could be interrupted due to VLC receiver saturation or due to a low SNR. In such situations, a VLC receiver's ability to adapt to the specific environment and to the specific context can be extremely important.  
In summary, the aims of the following tests are provided below:  
1. To investigate the system's ability to estimate the location of the sun relative to a VLC receiver based on the IR optical power received by a custom-made multi-angle light sensor;
2. To adjust the VLC receiver's FoV in accordance with the incident light and the incidence angle;
3. To experimentally determine the benefits associated with the use of the adaptive FoV VLC receiver.