Field Trial of a SDN-Controlled, Hybrid FiWi FSO/mmWave X-Haul With Zero-Touch Handovers and Record-High Data Rate for 6G

In the emerging era of 5G+/6G, flexibility and autonomous operation of Radio Access Networks (RANs) without strict bandwidth limitations or energy-waste trade-offs are actively being pursued to satisfy the immense capacity demands and time-varying nature of mobile networks. The current work reports the first field trial of a fully automated, Software Defined Network (SDN) controlled hybrid Fiber Wireless (FiWi) Free Space Optics (FSO)/millimeter-wave (mmWave) X-haul link with a record-high data-rate up to 100 Gb/s using real-time traffic. Specifically, the hybrid FiWi X-haul link relies on wavelength-tunable transmissions across an O-band FSO link or a C-band FiWi mmWave channel, being dynamically allocated and wavelength-routed by means of an all-passive O-band/C-band diplexer. A complete SDN algorithmic workflow that periodically polls the status of the wireless channel, triggering a fully automated handover to the optimum functional channel upon adverse weather conditions or channel outages is developed, relying exclusively on open-source and inter-operable SDN agent and network controller solutions. The hybrid link is initially evaluated at a cascaded transmission across a 1 km fiber and a 25 m-indoor wireless stages, achieving a periodic time-slotted operation with 25 $\mu$s beam-switching time, O/C-band crosstalk less than −30 dB and wide open eye diagrams with 6.8 dB Extinction Ratio (ER). Finally, the hybrid link is benchmarked in a 24-hour long, automated, zero-touch, outdoor setup with 1km fiber and 50 m wireless distance, providing robust rooftop-to-rooftop communication across two neighboring buildings with up to 100 Gb/s capacity, transporting real-time services and 4K-UHD video streaming with uninterrupted operation under both daylight and nighttime turbulent conditions with 5 Beaufort wind speed. The proposed real-time, automated hybrid FiWi FSO/mmWave link is the first to break the 10 Gb/s barrier of conventional edge networks, shaping a promising hardware-software X-haul solution towards survivable 5G+/6G RANs.