Visible Light Communications

Visible light communication (VLC) is an optical wireless communication technology that uses low-power light-emitting diodes (LEDs) to not only provide light, but also broadcast data [1–3]. LEDs are extremely energy-efficient and are expected to become widespread in general lighting applications. Because LEDs are solid-state lighting devices, they can be modulated at high speed compared to other lighting sources. VLC uses LEDs to send data by flashing light at speeds that are undetectable to the human eye. The widespread use of LEDs in traffic applications and the growing interest in intelligent transport systems (ITS) presents a number of opportunities for VLC applications. Data transmission using LED traffic lights and LED brake lights is a typical application [3, 4]. While previous studies have documented the effectiveness of vehicle-to-infrastructure (V2I) and vehicle-tovehicle (V2V) communication using radio technology in terms of improving automotive safety [5, 6], in the present article, we introduce the concepts of V2I-VLC and V2V-VLC. In V2I and V2V systems, VLC offers several advantages. Since VLC links are visible, installation of roadside equipment is much easier. Additionally, previously installed facilities, such as LED traffic lights or LED sign boards, can be used. Furthermore, since the transmitters, or LED light sources, are designed for lighting purposes (and thus generally have high radiation power), the signal-to-noise ratio (SNR) is high for VLC, while eye safety is maintained for dualuse lighting, defined here as VLC incorporated with LED illumination. The visible light spectrum is not regulated globally, and its bandwidth extends from 400 up to 790 THz. The large (390 THz) available bandwidth provides attractive opportunities for ITS applications. Furthermore, V2I and V2V communications using radio technology can be used simultaneously with VLC, with each using a different spectrum. VLC provides an additional feature if the receiver incorporates an image sensor or a camera. Specifically, by using image or video processing to detect and recognize moving vehicles, safety applications can be integrated. For example, as methods of enhancing driving safety, adaptive cruise control, collision warning, pedestrian detection, and providing range estimations for nearby vehicles are potential candidates for incorporation into VLC systems. In this article, we introduce VLC application to ITS while focusing on an image sensor as a reception device. After starting with an overview of an image sensor as a VLC reception device, ABSTRACT