RoF for Mobile Fronthaul

Use cases and requirements for sixth generation (6G) mobile communication systems have been discussed in some organizations. The peak data rate, minimum latency, and maximum connectivity are expected to be hundreds of Gbit/s, 100 μs, and tens of millions of devices/km2, respectively. Analog radio-over-fiber (A-RoF) technologies including intermediate frequency-over-fiber (IFoF) technologies have been studied for mobile fronthaul (MFH) links in the fifth generation (5G) and 6G mobile systems. This is mainly because, in the A-RoF/IFoF transmission systems, large-capacity and highly-spectral-efficiency optical transmission can be achieved by simple analog intensity modulation and direct detection (IMDD) scheme, and configuration of optical and mobile equipment in antenna sites can be simplified. In the future, these features will gain more importance as they can effectively reduce optical transmission costs and rapidly expand service areas. In this chapter, the overview of mobile communication systems is firstly explained. Radio access network (RAN) architecture, requirements for 6G mobile services, and key wireless communication technologies for 5G and 6G are included. Next, A-RoF and IFoF transmission systems for MFH application are explained as the main part of this chapter. Technical issues in such transmission systems and some of the solutions are introduced. Point-to-multipoint (PtMP) IFoF transmission systems for efficiently accommodating many antennas are also shown. Additionally, various frequency conversion technologies for IFoF systems, and analog beamforming technologies by controlling optical signals, especially for A-RoF systems are described.