Multi-User 6G Radio Access Networks: THz Fiber Wireless X-Haul of a Multi-Beam Millimeter Wave Antenna

The rise of the 6G era promotes massive broadband wireless connectivity in dense multi-user networks, equipped with flexible X-haul transport schemes. This work presents the first experimental demonstration of the end-to-end signal flow of a flexible THz Fiber Wireless (FiWi) X-haul that aggregates and simultaneously transports the multiple Intermediate Frequency over Fiber (IFoF) streams of a mmWave Multiple Input Multiple Output (MIMO) antenna on a single wavelength in the analog domain. Specifically, the FiWi X-haul transmission relies on a pair of 150 GHz antennas with 256 radiating elements placed after a 7 km-long fiber spool, acting as a THz wireless bridge that provides flexible, seamless last mile connectivity. In turn, mmWave access in the Radio Access Network (RAN) segment is provided by means of a cascaded MIMO Phased Array Antenna (PAA) hosting three analog Intermediate Frequency (IF) input ports with microwave filtering and RF beamsteering. The proposed THz FiWi multi-IFoF X-haul link transports three different V-band user beams, each supporting a 250Mbd QPSK signal with individual analog RF beamsteering anywhere within a 90^o sector, mapping each beam at a different transport IF. The proposed system distributes a 1.5 Gb/s data rate in three steerable beams anywhere in the 90° field of view of the MIMO antenna or to unleash a peak aggregate rate of >10 Gb/s at a single beam-direction, forming a flexible THz multi-IFoF X-haul of a multi-beam mmWave antenna on a single-wavelength and a promising roadmap for future multi-user 6G RANs.