Free Space Optical Communications for Intelligent Transportation Systems: Potentials and Challenges

As one of the key technologies of the intelligent transportation system (ITS), vehicle-to-everything (V2X) communications have received increasing attention. Because of the broad and unlicensed spectrum, free space optical (FSO) communications have become a potential technology for V2X communications. In this article, the implementation of FSO communications is introduced first. Afterward, for the three advantages of FSO communications in ITS, the concrete principle and implementation approaches are illustrated in detail. First, based on the adaptive illumination schemes, the communication range is expanded without visual interference caused by illumination. Second, with the help of mode division multiplexing (MDM) and wavelength division multiplexing (WDM), the communication rate is further increased. Third, integrating sensing and communication enables vehicles to effectively obtain information and improve traffic efficiency and safety. In addition, applications of FSO communications in various communication scenarios in ITS are described. To satisfy the complex requirements of communication, illumination, and sensing in traffic scenarios, a deep learning-enabled heterogeneous system of FSO and radio frequency is proposed. Furthermore, future applications and open issues are provided for further investigation.