## 3 Adaptive Field-of-View Visible Light Communication: Concept and Prototype Development
### Presentation of the VLC Transmitter Used for the Experiments  
The prototype used for the experimental testing consisted of a 20 cm diameter traffic-light VLC transmitter and a PIN photodiode-based VLC receiver. From a hardware point of view, the VLC transmitter comprised LED light sources (in this case, an LED traffic light), a digital switching driver, and a 600 MHz ARM Cortex M7 processor-based microcontroller. The traffic light served as the optical source for transmitting encoded data. For this experiment, in order to demonstrate that the concept is suitable for real-life situations, a commercial traffic light was used. It is important to emphasize that the lighting characteristics of the LED traffic light were not modified, neither by increasing the optical output nor by modifying the light distribution pattern. The traffic light LEDs were controlled by a digital switching driver, which used OOK modulation to send the data stream generated by the microcontroller. In turn, the microcontroller served as the central processing unit of the VLC transmitter, being responsible for generating and encoding the data stream, and also for building/encapsulating the data frame. The microcontroller's software comprised algorithms for Manchester encoding, which involved converting each data bit into a pair of consecutive OOK symbols and generating frames at various data rates between 11 and 250 kb/s. The VLC transmitter used an asynchronous communication mode, meaning that the VLC transmitter and receiver were not synchronized. Asynchronous communication enabled data packets of variable lengths and flexible timing, which is suitable for applications with unpredictable data rates, variable transmission requirements, and decentralized networks. Therefore, this is an adequate option for vehicular applications. In terms of optical specifications, the LED-based traffic light had an optical irradiance of 130 \(\mu\)W/cm\({}^{2}\) (measured at a 1 m distance), and a transmitter's half-angle of \(\pm\)15\({}^{\circ}\). Overall, the VLC transmitter complied with standard optical power levels and used off-the-shelf components to ensure its cost-effectiveness, ease of implementation, and comparable results with real-life situations. Figure 1 presents the schematic block of the VLC transmitter. Discussions on the VLC Receiver Architecture, Emphasizing the Structure and Importance of the Adaptive FoV Unit  
The VLC receiver is the most important component in a VLC system, being responsible for detecting, processing, and extracting the information from the modulated light signals [47]. From a purpose point of view, the VLC receiver's structure can be divided into three major blocks: the front-end optical collecting system, the signal-processing component, and the data-processing block. Figure 1 presents the architecture of the proposed concept. The front-end optical collecting system is developed around the photosensitive element, which is responsible for the transformation of incident light power into a proportional electrical current. As in most cases, a PIN photodiode is used, due to its low response times and high sensitivity. The PIN photodiode is connected in a transimpedance circuit, providing a fair tradeoff between the bandwidth, noise, sensitivity, and dynamic range. As the output signal is dependent on the incident light power, a 2-inch optical lens is used to increase the collecting area. The optical lens focuses the incident light on the photodiode's surface. As a result, the optical lens restricts the FoV to \(\pm 22^{\circ}\). In order to enhance the SNR, a 40 nm red optical filter is used to reject the upper spectrum of ambient noise. In this work, the elements of novelty were introduced at the level of the front-end optical collecting system. Different from other solutions, this newly developed prototype integrated an optical-noise-sensor module coupled with the optical collecting system.