Design and deployment of optical x-haul for 5G, 6G, and beyond: progress and challenges [Invited]

Review article, 2023

Sixth generation (6G) wireless technology, which is the next giant leap in the evolution of wireless communication, has been gaining great interest from academia, industry, and the general public due to its capabilities and the applications that are expected to be supported. Optical x-haul is becoming increasingly important as a key element of the 6G ecosystem due to the increasing demand for high data rates and low latency with the emergence of new 6G applications and use cases. The ability of optical x-haul to support high data rates and low latency along with its scalability and high-reliability performance makes it an essential transport technology for future wireless networks of 6G and beyond. However, optical and wireless technologies operate in different domains and with different standards. Therefore, integration of optical x-haul and 6G needs careful consideration with emphasis on bringing network intelligence softwarization. This is particularly important in supporting the quality of service requirements of emerging applications in the most cost-effective and sustainable manner. To this end, this paper reviews the research that has been carried out in the investigation of the optical x-haul network in a hybrid fiber-wireless system to cater to the next generation of wireless networks. Especially, we review the research carried out in open radio access network architecture, coordination functionalities in radio-over-fiber networks, optimization frameworks that can be used to jointly optimize wireless and optical network deployments, and reconfigurable optical x-haul. We conclude the paper by providing insights into research challenges that we need to overcome in integrating optical x-haul in the 6G ecosystem to support emerging applications.