Optical wireless communication (OWC) is an excellent complementary solution to its radio frequency (RF) counterpart. OWC technologies have been demonstrated to be able to support high traffic generated by massive connectivity of the Internet of Things (IoT) and upcoming 5th generation (5G) wireless communication systems. As the characteristics of OWC and RF are complementary, a combined application is regarded as a promising approach to support 5G and beyond communication systems. Hybrid RF/optical and optical/optical wireless systems offer an excellent solution for recovering the limitations of individual systems as well as for providing positive features of each of the technologies. An RF/optical wireless hybrid system consists both RF and optical-based wireless technologies, whereas an optical/optical wireless hybrid system consists two or more types of OWC technologies. The co-deployment of wireless systems can improve system performance in terms of throughput, reliability, and energy efficiency of individual networks. This study surveys the state of the art and key research directions regarding optical wireless hybrid networks, being the first extensive survey dedicated to this topic. We provide a technology overview of existing literature on optical wireless hybrid networks, such as RF/optical and optical/optical systems. We consider the RF-based macrocell, small cell, wireless fidelity, and Bluetooth, as well as optical-based visible light communication, light fidelity, optical camera communication, and free-space optical communication technologies for different combinations of hybrid systems. Moreover, we consider underwater acoustic communication for hybrid acoustic/optical systems. The opportunities brought by hybrid systems are presented in detail. We outline important challenges that need to be addressed for successful deployment of optical wireless hybrid network systems for 5G and IoT paradigms.

中文翻译：

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光无线混合网络：趋势、机遇、挑战和研究方向

光无线通信 (OWC) 是其射频 (RF) 对应物的绝佳补充解决方案。OWC 技术已被证明能够支持由物联网 (IoT) 和即将推出的第 5 代 (5G) 无线通信系统的大规模连接产生的高流量。由于 OWC 和 RF 的特性是互补的，因此组合应用被认为是支持 5G 及以后通信系统的有前途的方法。混合射频/光和光/光无线系统为恢复单个系统的局限性以及提供每种技术的积极特性提供了极好的解决方案。射频/光无线混合系统由射频和基于光的无线技术组成，而光/光无线混合系统包含两种或更多类型的 OWC 技术。无线系统的共同部署可以在单个网络的吞吐量、可靠性和能效方面提高系统性能。本研究调查了有关光无线混合网络的最新技术和关键研究方向，是第一个专门针对该主题的广泛调查。我们提供了有关光无线混合网络（例如射频/光和光/光系统）的现有文献的技术概述。我们考虑了基于射频的宏蜂窝、小蜂窝、无线保真和蓝牙，以及基于光的可见光通信、光保真、光学相机通信和自由空间光通信技术，用于混合系统的不同组合。而且，我们考虑混合声/光系统的水声通信。详细介绍了混合系统带来的机遇。我们概述了成功部署用于 5G 和物联网范式的光无线混合网络系统需要解决的重要挑战。