Relay-Assisted Technology in Optical Wireless Communications: A Survey

When the distance between the source and the target is long, the signal will be affected by atmospheric turbulence, weather conditions and obstacles, which cannot support the information transmission. One of the existing solutions is to use relay-assisted technology (RAT). It makes the communications between the source and the destination possible under better channel conditions by setting up relay between the source and the destination. There are few comprehensive articles about relay-assisted technology in OWC. To fill this gap, this paper introduces the RAT of indoor optical wireless communications (IOWC), outdoor optical wireless communications (OOWC) and underwater optical wireless communications (UOWC) in different application scenarios, which has a better effect than direct communication between source and destination. The relay protocols, channel models, modulation techniques under three relay modes are reviewed. Finally, challenges of RAT in OWC are put forward and potential solutions are also given.