The sixth generation (6G) mobile systems will create new markets, services, and industries making possible a plethora of new opportunities and solutions. Commercially successful rollouts will involve scaling enabling technologies, such as cloud radio access networks, virtualization, and artificial intelligence. This paper addresses the principal technologies in the transition towards next generation mobile networks. The convergence of 6G key-performance indicators along with evaluation methodologies and use cases are also addressed. Free-space optics, Terahertz systems, photonic integrated circuits, softwarization, massive multiple-input multiple-output signaling, and multi-core fibers, are among the technologies identified and discussed. Finally, some of these technologies are showcased in an experimental demonstration of a mobile fronthaul system based on millimeter 5G NR OFDM signaling compliant with 3GPP Rel. 15. The signals are generated by a bespoke 5G baseband unit and transmitted through both a 10 km prototype multi-core fiber and 4 m wireless V-band link using a pair of directional 60 GHz antennas with 10° beamwidth. Results shown that the 5G and beyond fronthaul system can successfully transmit signals with both wide bandwidth (up to 800 MHz) and fully centralized signal processing. As a result, this system can support large capacity and accommodate several simultaneous users as a key candidate for next generation mobile networks. Thus, these technologies will be needed for fully integrated, heterogeneous solutions to benefit from hardware commoditization and softwarization. They will ensure the ultimate user experience, while also anticipating the quality-of-service demands that future applications and services will put on 6G networks.

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We present a fixed mobile convergence topology for analog intermediate frequency over fiber (A-IFoF)/millimeter-wave (mmWave) transmission, benefiting from the reuse of the deployed passive optical network (PON) infrastructure, towards future mobile fronthaul architectures. Powerful fully programmable gate array boards located inside the access nodes convert the Ethernet-based traffic to orthogonal frequency-division multiplexing (OFDM)-modulated intermediate frequency (IF) waveforms, supporting the A-IFoF propagation through the optical legacy infrastructure. Coexistence of the 5G traffic with the residential legacy traffic for the field propagation is achieved through utilization of unused C-band channels and wavelength-division multiplexing. To this extent, we experimentally demonstrate the downlink operation of a converged A-IFoF/mmWave link, over Telecom Italia’s legacy infrastructure located at Turin. Four-quadrature amplitude modulation (QAM)-OFDM and 16QAM-OFDM IF signals with ∼ 200 M H z and 400 MHz bandwidth [considered within the 3rd Generation Partnership Project (3GPP) New Radio specifications] were generated through a radio frequency system-on-chip platform and optically multiplexed with the legacy fiber-to-the-home services. After propagation to the field, the A-IFoF stream was directly fed to a directional wireless link operating at 60 GHz. Successful PON/over-the-air transmission with error vector magnitude (EVM) values well below the 3GPP ( < Privacy Policy and Terms of Service apply.