Abstract
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.
Highlights
Go back to history, human beings have been using optical communication technology for a long time
The results show that the performance of the two-way multi-hop system is improved obviously compared with the one-way multi-hop system and the two-way dual-hop system
In this survey, the basic knowledge of Optical wireless communications (OWC) under relay technologies are discussed, including indoor optical wireless communications (IOWC), outdoor optical wireless communications (OOWC) and underwater optical wireless communications (UOWC). For these three relay systems, OOWC link is subject to the Gamma-Gamma distribution, and the RF hop is influenced by the Nakagami-M distribution
Summary
Human beings have been using optical communication technology for a long time. RELAY FORMS IN OUTDOOR OPTICAL WIRELESS COMMUNICATIONS OOWC is that modulated laser beams transmit optical signals through free space in wireless way [41] It has multiple advantages, such as no electromagnetic interference, larger band-width, unlimited spectrum, high transmission rate, good anti-interference and anti-interception. In the process of the wireless network transmission, when unable to direct communications between source and destination, multi-hop technique is introduced Under these communications, relay nodes are responsible for forward information. A dual-hop relay network is considered in [140], which is sufficient to reliably transmit underwater data over long distances without expensive and complex networking infrastructure Under this scenario, multiple sensors transmit the data to relay in DF protocol by using UOWC link. C. DESTINATION TERMINAL IN OPTICAL WIRELESS COMMUNICATIONS The relay receives the transmitted signal and sends it to the destination via the RF link.
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