###### Abstract  
Vehicle-to-vehicle communication based on visible light communication has gained much attention. This work proposes a smart license plate receiver incorporated with a fluorescent concentrator, enabling a fast vehicle-to-vehicle communication with a large field of view and high optical gain. Communication performance is experimentally analyzed using off-the-shelf light-emitting diode-based headlamps for low-latency direct line of sight channel. Additionally, a blue laser diode-based beam-steering and tracking system, through image processing of taillights with a steerable mirror, is investigated. Data rates of 54 Mbps from the headlamps and 532 Mbps from the beam-steering channel with \(\pm 25^{\circ}\) are demonstrated. In addition, real-time video streaming through the beam-steering channel is presented. Li-Fi; visible light communication; VLC; optical wireless communication; OWC; vehicle-to-vehicle communication; V2V +
Footnote †: journal: Sensors  
00222222485 and red LED with multiple Tx/Rx system was implemented to minimize the detrimental impact in Refs. [7; 8]. To mitigate the effect of sunlight, a method of moving transmitter (Tx) and receiver (Rx) adaptively to the ambient light was introduced [9]. However, there are still unresolved challenges left for the development of V2V-VLC technology. Among them are the narrow field of view (FoV), LOS blockage, and misalignment. Typical VLC receivers require optics such as lenses or concentrators, leading to the limited FoV. Even within the FoV, the V2V channel between two vehicles is susceptible to another vehicle intervening in-between and by a vibrational and angular motion of the end device. A fluorescent concentrator (FC) is a promising solution for enhancing the FoV of V2V-VLC system. FC is a non-imaging optic that accepts the incident photons from wide angles, converts them into longer wavelength photons, and guides them to a narrow edge through the total internal reflection [10]. Hence, a large FoV and high optical gain beyond the Etendue limit is provided, with the gain of ~4 compared to the conventional concentrators [11]. Additionally, with a short fluorescent lifetime, FC can accommodate a high bandwidth signal, overall improving the signal-to-noise ratio (SNR) in a wide frequency range. For the link disconnection by the LOS blockage and the misalignment, a promising solution is to construct a beam-steering network with the surrounding vehicles equipped with a stable tracking method. To show the feasibility of the beam-steering technique in V2V-VLC, an onboard sensors architecture and cooperative data sharing between vehicles to estimate the pointing directions were studied in Ref. [12]. Additionally, a cost-effective beam-steering system based on a fluorescent reflector and image processing was introduced for device-to-device (D2D) V2V [13]. In this research, FC-coupled license plate with a beam-steering-technique-based V2V-VLC system is proposed. The unique features of FC (high gain and wide FoV) are tested under various practical cases. Off-the-shelf white LED (WLED) headlamps to construct a direct communication link and a narrow-beam blue laser diode (LD) channel to the FC-coupled license plate is evaluated. The position information obtained by two cameras beside the LD beam-steering module is utilized for the beam steering. With DC biased OFDM (DCO-OFDM) scheme, the communication performances of the onboard WLED channel and the beam-steered blue LD channel are investigated. The rest of this work is organized as follows. Section 2 presents a description of the proposed V2V-VLC architecture, including headlamps, taillights, cameras, and a license plate incorporated with FC, followed by an image detection and beam-steering mechanism. In Section 3, to show the feasibility of the proposed system, a series of experimental analyses is presented, including the characterization of the FC-coupled license plate, investigation on the range of beam steering and tracking, and analysis on the communication performances.