I. Introduction
Optical wireless communications (OWCs) not only can improve the inconvenience of both architecting and using the existing wired optical fiber network caused by the limitations for the environment and optical fiber cables, but also can solve the traditional infrared (IR) system [1], which has disadvantage of short transmission distance and low transmission rate. Moreover, OWCs also can provide advantages of having high data transmission security and confidentiality, without electromagnetic wave problems caused by the traditional radio communication propagation and satisfying the lighting needs of the human beings in daily life at the same time [2], [3]. Therefore, OWCs have gradually attracted much attention in the recent years, and many new OWC architectures which focused on various research issues and solutions, such as system performance, transmission data rate, peak-to-average power ratio (PAPR) performance, system spectrum efficiency, and so on, were proposed successively [3]–[5].