## 3 Adaptive Field-of-View Visible Light Communication: Concept and Prototype Development
### Experimental Results  
#### 4.2.1 Experimental Results for the Optical Noise Localization Component  
As previously mentioned, the experimental investigation was carried out for an entire day. The test setup is presented in Figure 4, showing the static experimental configuration as well as the sun's exact trajectory during the tests. In order to avoid shadowing, we chose to place the receivers and the transmitter at the top level of two buildings located 50 m apart. As one can see, the 50 m distance made the VLC transmitter difficult to perceive.  
The purpose of the first test was to determine if the custom-made light-detection sensor was able to determine the sun's position relative to the VLC receiver. This aspect is very important to the next phase of the experiments, as these results will influence the adaptation of the VLC receiver's FoV. Figure 5 shows a satellite view of the university campus where the tests were carried out. This figure shows the position of the VLC transmitter and VLC receivers, as well as the sun's trajectory during these tests. In this case, the exact sun trajectory was established based on [48]. As one can see, in the first part of the day, the VLC receiver was not exposed to direct sunlight, but rather was only exposed to diffuse light. Later on, after 12:30 p.m., the sun began to enter the FoV of the VLC receivers. Around 4 p.m., the sun was right above the VLC transmitter, pointing directly toward the VLC receivers. After 4 p.m., the sun moved from this orientation as it approached sunset, and after 5 p.m., the sun's influence was blocked due to a large tree (Figure 4). Additionally, the experimental tests were affected by cloudy weather from around 10:50 a.m. to 12:45 p.m.  
Figure 3: Illustration of the envisioned testing scenario: two VLC receivers, one without an adaptive FoV and one with an adaptive FoV, were monitored for an entire day. As the position of the sun varied throughout the day, it changed the impact on a 50 m VLC link between an LED-based traffic light VLC transmitter and two VLC receivers.  
Figure 4: Experimental testing setup, showing the VLC transmitter, the VLC receivers, and the sun’s trajectory during the tests.  
Figure 5: Satellite view showing the location of the VLC transmitter and VLC receivers together with the sun’s angles during the day.  
In accordance with this setup, Table 1 summarizes the results of the experiments, which confirmed the multi-angle light sensor's ability to estimate the sun's relative location within a 10\({}^{\circ}\) limit for both axes. This was possible due to a mediation algorithm that limits the effects of certain estimation errors, and that made an assessment concerning the sun's location based on the average of several light-intensity measurements. Additionally, it has been previously observed that the response of certain photodiodes is not in line with the response of other ones, a fact that was attributed to imprecise 3D printing and photodiode positioning within the multi-angle light sensor. Consequently, the effect of certain sensitivity discrepancies among photodiodes was optimized and calibrated with specific software algorithms. Additionally, to reduce the effects of isolated light intensity measurement errors, the decision concerning the sun's location was made based on an averaging algorithm that considered multiple photodiode readings. It should also be mentioned that, when the multi-angle did not detect a significantly higher intensity at a certain angle, the sensor established that it was exposed to diffuse light. Under such conditions, the FoV was adapted based on the light intensity measurement, disregarding the sun's location. Again, as the photodiodes only work with the sun's IR component, a calibration of the light intensity measurement was required.