The current work presents the first experimental demonstration of real-time Ethernet (ETH) trial services and 4K-Ultra High Definition (UHD) video application transmission over a 2λ Wavelength Division Multiplexing (WDM) analog Fiber-Wireless (FiWi) mmWave X-haul network, supporting dynamic flexible capacity allocation through an integrated silicon photonic Si ₃ N ₄ Reconfigurable Optical Add Drop Multiplexer (ROADM) and 60 GHz wireless transmission across a 7 m V-band link distance, while controlled by a Software Defined Network (SDN) controller based on Open Daylight. Analog X-haul transport of the radio signals is based on an Intermediate Frequency over Fiber (IFoF) scheme centered at 1.5 GHz using an Orthogonal Frequency Division Multiplexing (OFDM) radio-waveform with a bandwidth of 204 MHz, generated by a Field Programmable Gated Array (FPGA)-based RF System-on-Chip (SoC) processor that converts on-the-fly the real-time ETH downlink traffic to analog radio and vice-versa for the uplink. Dynamic allocation of the X-haul traffic capacity is handled through the use of the 802.1Q Virtual Local Area Network (VLAN) tag-mechanism, which controls the forwarding operation to the proper DAC and InP EML for optical modulation using Intensity Modulation/Direct Detection (IM/DD) schemes, while the wavelength routing operation is handled by the low-loss four-port Si ₃ N ₄ ROADM featuring only 2.5 dB fiber-to-fiber losses based on a cascaded MZI-interleaver design on the TriPleX platform, routing the real-time traffic to a second mmWave antenna site. Detailed measurements and traffic statistics indicate end-to-end latency of less than 260 μs and a packet loss less than 0.0054% across a dynamic range of at least 6.5 dB in the optical domain, while the high user bandwidth and signal quality are validated by an uninterrupted 4K-UHD video transmission across the FiWi X-haul mmWave transport network. The current work aims to shape a complete technology roadmap for Point-to-Multipoint FiWi transport network architectures with high spectral efficiency X-haul transport for dense areas and 5G/6G hotspots of future mmWave Centralized Radio Access Networks (C-RANs).

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 ( < 12.5 % ) requirements for 5G New Radio was demonstrated, with a 10.5% EVM for 16QAM-OFDM modulated with 400 MHz bandwidth.

In future mobile networks, the evolution of optical transport architectures enabling the flexible, scalable interconnection of Baseband Units (BBUs) and Radio Units (RUs) with heterogeneous interfaces is a significant issue. In this paper, we propose a multi-technology hybrid transport architecture that comprises both analog and digital-Radio over Fiber (RoF) mobile network segments relying on a dynamically reconfigurable optical switching node. As a step forward, the integration of the discussed network layout into an existing mobile infrastructure is demonstrated, enabling the support of real-world services through both standard digital and Analog–Intermediate- Frequency over Fiber (A-IFoF)-based converged fiber–wireless paths. Emphasis has been placed on the implementation of a real-time A-IFoF transceiver that is employed through a single embedded fully programmable gateway array (FPGA)-based platform that serves as an Ethernet to Intermediate Frequency (IF) bridge for the transmission of legacy traffic over the analog network segment. The experimental evaluation of the proposed concept was based on the dynamic optical routing of the legacy Common Public Radio Interface (CPRI), 1.5 GBaud analog-intermediate frequency-over-fiber (A-IFoF)/mmWave and 10 Gbps binary optical waveforms, showing acceptable error vector magnitude (EVM) values for the complex radio waveforms and error-free operation for binary optical streams, with Bit Error Rate (BER) values less than 10⁻⁹. Finally, the end-to-end proof-of-concept demonstration of the proposed solution was achieved through the delivery of 4K video streaming and Internet Protocol (IP) calls over a mobile core network.

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.

We present a novel technique for dispersion compensation by exploiting the filtering properties of a fully reconfigurable serially coupled microring resonator (MRR) structure in analog intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless 5G and beyond 5G(B5G)-oriented mobile fronthaul. To this extend, we demonstrate simulation and experimental results on analog photonic processing of 1 Gbaud Quadrature Phase Shift Keying (QPSK) modulated radio signal. By tuning filter's bandwidth in the range of 26 - 69 GHz, and resonance within a resonance free spectral range (FSR) range, dispersion induced power fading mitigation was achieved, for a set of widely adopted intermediate frequencies (IFs) and transmission distances. Analytical calculations carried out in MATLAB environment, highlighting significant improvement of transmission system output power, whereas are verified via transmission system simulations, resulting to error vector magnitude (EVM) improvement up to ~ 30%. Experimental results verified both analytical and transmission simulation results for a series of IFoF downlink transmission system configurations. For widely used wireless transmission configuration at 8.5 GHz IF, by tuning the filter to appropriate bandwidth of 14 GHz and resonance peak properly, successful fiber wireless transmission for over 25 km of fiber was demonstrated, achieving 16.9% EVM for QPSK, below the 3GPP (<17.5%) requirements for 5G NR.

We demonstrate a SOI ring-based, analog phase processing method to manage the dispersion induced power fading of DSB IFoF. Experimental results in an IFoF/V-band Fronthaul link, revealed improved EVM performance of 1 Gbaud QPSK signals.