Cooperative visible light communications: An overview and outlook

The evolution of data-intensive services and applications continues to drive the need for higher data rates in wireless communication systems, consequently depleting the radio frequency (RF) spectrum. Due to the unlicensed and enormous bandwidth available in the visible light (VL) spectrum, the emergence of visible light communication (VLC) has been considered a potential solution to alleviate the constraints associated with RF spectrum scarcity. However, the line-of-sight requirement and the inability of VL to penetrate opaque obstacles remain a daunting challenge in realizing a wider coverage area. The incorporation of cooperative communication in VLC systems serves as one of the primary solutions to address this challenge. Though various investigations are currently being conducted in this domain, a holistic report of various advances, solution approaches, and design challenges has not been captured in the open literature. Therefore, in this paper, our main goal is to present a review of the state-of-the-art research on cooperative VLC systems. Firstly, we provide a background discussion to establish the relationship between various components of cooperative VLC systems from a theoretical and analytical perspective. Secondly, we categorize various contributions in this direction under media access control (MAC), hybrid VLC-RF, power line communication-VLC (PLC-VLC), and VLC with energy harvesting. Based on the established categories, we identify various system design and evaluation methods, optimization problems, solution approaches adopted to tackle the problems, and their limitations. Thirdly, we identify various insights obtained from the presented papers that could serve as guidelines for practical system design. Finally, various design challenges and open areas for future research are identified.