Toward 6G Optical Fronthaul: A Survey on Enabling Technologies and Research Perspectives

The anticipated launch of the Sixth Generation (6G) of mobile technology by 2030 will mark a significant milestone in the evolution of wireless communication, ushering in a new era with advancements in technology and applications. 6G is expected to deliver ultra-high data rates and almost instantaneous communications, with three-dimensional coverage for everything, everywhere, and at any time. In the 6G Radio Access Networks (RANs) architecture, the Fronthaul connects geographically distributed Remote Units (RUs) to Distributed/Digital Units (DUs) pool. Among all possible solutions for implementing 6G fronthaul, optical technologies will remain crucial in supporting the 6G fronthaul, as they offer high-speed, low-latency, and reliable transmission capabilities to meet the 6G strict requirements. This survey provides an explanation of the 5G and future 6G optical fronthaul concept and presents a comprehensive overview of the current state of the art and future research directions in 6G optical fronthaul, highlighting the key technologies and research perspectives fundamental in designing fronthaul networks for 5G and future 6G. Additionally, it examines the benefits and drawbacks of each optical technology and its potential applications in 6G fronthaul networks. This paper aims to serve as a comprehensive resource for researchers and industry professionals about the current state and future prospects of 6G optical fronthaul technologies, facilitating the development of robust and efficient wireless networks of the future.

I. Introduction

Recently, particularly in the aftermath of the COVID-19 pandemic, communication networks have become increasingly important in all aspects of our lives (i.e., healthcare, smart manufacturing, distance learning, smart cities, etc). For that, the number of devices connected to the Internet is expected to grow significantly each year, leading to a substantial increase in traffic volumes served by mobile networks. By 2030, it is projected that these networks will handle at least 5000 Exabytes of data per month, while global data traffic is forecasted to exceed 3 Zetabytes. Additionally, the user mobile data usage will rise from 5 GB in 2020 to more than 250 GB per month in 2030 as shown in Fig. 1 [1]. Fig. 1.

Estimated global mobile traffic and user data traffic from 2020 to 2030 based on ITU-R Report M.2370-0 [1].