# Vehicular Visible Light Communication for Intersection Management +
## 3 V-VLC Vehicular Communication  
### V2X Communication System  
Vehicular communication is one of the key enabling technologies for future Intelligent Transportation Systems (ITSs) [20, 21, 22]. The V-VLC system makes use of outdoor light sources (street lamps and traffic lights) as the access points, which can serve for both lighting and communication purposes, providing drivers with outdoor wireless communications. The system is composed of two modules: the transmitter and the receiver located at the infrastructures and at the driving cars. The block diagram and the transmitter and receiver relative positions of the V-VLC system are presented in Figure 1. Both communication modules (transmitter and receiver) are software defined, where modulation/demodulation can be programed. To realize both the communication and the street illumination, white light tetra-chromatic sources are used, providing a different data channel for each chip. Each luminaire is composed of four white LEDs framed at the corners of a square (see Figure 1a). At each node, only one chip of the LED is modulated for data transmission, the Red (R: 626 nm), the Green (G: 530 nm), the Blue (B: 470 nm) or the Violet (V: 390 nm), while the others provide a constant current for white perception. The luminous intensity of each emitter is regulated by the driving current for white perception by the human eye and the divergence angle is approximately 120\({}^{\circ}\). Data are encoded, modulated and converted into light signals emitted by the transmitters. Modulation and digital-to-analog conversion of the information bits are performed using signal processing techniques. This way, information is modulated onto the intensity of the light that is emitted by the transmitter and is transferred to receivers installed in the vehicles or infrastructures. The signal propagating through the optical channel and a VLC receiver, at the reception end of the communication link, is responsible for extracting the data from the modulated light beam. It transforms the light signal into an electrical signal that is subsequently decoded to extract the transmitted information. Figure 1: (**a**) Block diagram and transmitters and receivers and 3D relative positions of the VLC system. (**b**) Illustration of the coverage map in the unit cell: footprint regions (#1–#9) and steering angle codes (2–9). The core element of the receiver is a photodetector that converts the optical power into an electrical current. The VLC photosensitive receiver is a double pin/pin photodetector based on a tandem heterostructure, p-i\({}^{\prime}\)-n/p-i-n, sandwiched between two conductive transparent contacts. The front, thin pi\({}^{\prime}\)n structure made of a-SiC:H exhibits high absorption to short wavelengths (violet and blue light) and high transparency to the long wavelength (red light). In opposition, the back, thicker pin structure based on a-Si:H absorbs long wavelengths (red light), and the green light is absorbed in both structures. The device selectivity is tuned externally using reverse bias (\(-8\) V) and optical steady-state illumination of short wavelength (\(400\) nm). Due to its tandem structure, the device is an optical controlled filter able to identify the wavelengths and intensities of the impinging optical signals [23; 24; 25]. It offers high sensitivity and linear response, under irradiation. Its fast response enables high-speed communications. The generated photocurrent is processed using a transimpedance circuit, giving rise to a proportional voltage that is processed, by using signal conditioning techniques (adaptive bandpass filtering and amplification, triggering and demultiplexing). Finally, the data signal is reconstructed at the data processing unit (digital conversion, decoding and decision) [26; 27].