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The continuous advancement of wireless mobile communication necessitates an increase in the allocated frequency bands for each generation. Consequently, higher frequency photodiodes are required in analog radio-over-fiber (ARoF) fronthaul solutions. However, the limited available bandwidth in the wireless domain poses challenges to efficiently utilize the capacity of these photodiodes. To overcome this obstacle, this paper explores the utilization of a single-photodiode base station configuration to enable hybrid digital radio-over-fiber (DRoF) and ARoF transmission. Furthermore, it proposes a straightforward signal processing approach to effectively separate the distinct analog and digital radio-over-fiber signals. To evaluate the feasibility of the proposed signal processing method, software simulations were conducted. The initial findings indicate that the combination of a single-photodiode base station configuration and the suggested signal processing approach holds promise for hybrid digital and analog radio-over-fiber systems. It demonstrates the potential to minimize the number of required photodiodes, thus improving efficiency in the context of limited available bandwidth.

We propose the concept and report the implementation of a Gbps hybrid full-duplex analog radio-over-fiber (A-RoF)/visible light communication (VLC) laser diode (LD)-based system for beyond the fifth generation (B5G) of mobile network applications. Such hybrid optical wireless architecture is composed of a 3-km single-mode fiber fronthaul based on the A-RoF technology, followed by a 1.3 m VLC-LD-based access network. The latter one employs two counter-propagating visible light beams by using dichroic cube filters (DCFs) at the transmitter and receiver side, enabling the full-duplex mode, and avoiding the use of individual optical filters. As a proof of concept, we experimentally demonstrate a successful deployment of 5G New Radio (NR) hybrid full-duplex A-RoF/VLC system. The system performance is evaluated in terms of root mean square error vector magnitude (EVM RMS), in accordance with the 3rd Generation Partnership Project (3GPP) requirements, and as a function of modulation order. The experimental results demonstrate a downlink throughput of 600 Mbit/s and an uplink throughput of 420 Mbit/s, aligning with the digital performance requirements set by 3GPP. • We have successfully demonstrated, for the first time in literature, a hybrid full-duplex architecture composed of single-mode fiber (SMF) fronthaul based on the analog radio over fiber (A-RoF) technology followed by a red and blue VLC-Laser-Diode-based access network. • To the best of our knowledge, we pioneerly report the use of a dichroic cube filters (DCFs) applied to a VLC system to enable full-duplex FiWi system implementation. In the VLC optical setup, DCFs were used at the transmitter and receiver sides, with the propose of directing and filtering visible beam lights for avoiding the use of discrete filters. • The proof of concept uses real 5G new radio (5G NR) signals to evaluate the system performance in terms of root mean square error vector magnitude (EVM RMS) in accordance to the 3rd Generation Partnership Project (3GPP), as a function the RF input power and modulation scheme. [ABSTRACT FROM AUTHOR]

A bidirectional wavelength division multiplexing (WDM) analog radio-over-fiber (A-RoF) mobile fronthaul (MFH) link is enhanced using photonic integrated devices. Two key photonic integrated devices are combined in the A-RoF link: an 8-channel InP directly modulated laser (DML) transmitter and a 32×100-GHz silicon array waveguide grating (AWG). The DML transmitter has 8 parallel monolithically integrated distributed feedback lasers, enabling cooperative and reconfigurable downlink analog transmission. Moreover, the 32×100-GHz AWG is featured by low insertion loss (

With the rise of 5G and beyond, the ever-increasing data-rates demanded by mobile access are severely challenging the capacity of optical fronthaul networks. Despite its high reliability and ease of deployment, legacy digital radio-over-fiber (RoF) technologies face an upcoming bandwidth bottleneck in the short term. This has motivated a renewed interest in the development of analog RoF alternatives, owing to their high spectral efficiency. However, unlike its digital counterpart, analog RoF transmission requires a highly linear transceiver to guarantee signal fidelity. Typical solutions exploited in recent research works tend to adopt the use of bulky benchtop components, such as directly modulated lasers (DML) and photodiodes. Although this provides a convenient and quick path for proof-of-concept demonstrations, there is still a considerable gap between lab developments and commercial deployment. Most importantly, a key question arises: can analog-RoF transceivers meet the 5G requirements while being competitive in terms of cost and footprint? Following this challenge, in this work we exploit the use of a low-cost commercial off-the-shelf (COTS) small form-factor pluggable (SFP) transceiver, originally designed for digital transmission at 1 Gbps, which is properly adapted towards analog RoF transmission. Bypassing the digital electronics circuitry of the SFP, while keeping the original transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we demonstrate that high-performance 5G-compatible transmission can be performed by reusing the key built-in components of current low-cost SFP-class transceivers. Particularly, we demonstrate error vector magnitude (EVM) performances compatible with 5G 64QAM transmission both at 100MHz and 400MHz. Furthermore, employing a memory polynomial model for digital pre-distortion of the transmitted signal, we achieve 256QAM-compatible performance at 100MHz bandwidth, after 20 km fronthaul transmission.

Towards enabling bandwidth-hungry 5G applications, a Fiber-Wireless (FiWi) mobile fronthaul architecture is experimentally presented supporting the co-existence of spectrally efficient analog transport formats with Digital Radio over Fiber transport schemes, combined with millimeter wave (mmWave) high-capacity wireless channels. Flexible transport network reconfiguration is proposed by means of a low-loss 1 × 4 Si3N4 Reconfigurable Optical Add/Drop Multiplexer (ROADM) on TriPleX platform, selectively dropping four FiWi mmWave fronthaul links to four different antenna location. Detailed investigations of the proposed system are reported, including frequency characterization, multi-stage EVM penalty study and analog/digital traffic coexistence PHY layer feasibility. Following, four 10 Gb/s multi-band 16-QAM WDM FiWi analog IFoF links are transmitted through 10km fiber and 1-m directional V-band antennas and flexibly reconfigured by a Si3N4 ROADM, achieving a record 40 Gb/s wavelength-routed fronthaul capacity for mmWave 5G, while simultaneously meeting multiple 5G Use Cases within 3GPP requirements. [ABSTRACT FROM AUTHOR]

Analog radio over fiber is attracting interest as a low-cost solution for high-frequency band distributed antenna systems (DAS). DAS demands the beamforming, TDD timing switching, and CLK synchronization of each distributed antenna section (or remote radio unit (RRU)), but as the number of optical carriers used for RRU control increases, the result is an undesirable increase in RRU complexity. In this paper, we propose and demonstrate a wireless system that can simultaneously transmit, via a single optical carrier, an analog main signal and a control signal (beamforming, TDD, and CLK signals) by subcarrier multiplexing (SCM). Simulations show that the signal quality degradation caused by nonlinearities in the optical modulator during SCM transmission can be avoided by properly designing the input power balance between the analog main signal and the control signal. We also conducted experiments on the downlink transmission of 256 QAM-modulated 5G NR signals by connecting a CS-RRU pair with a 20-km SMF. According to our OTA evaluation using a millimeter-wave band antenna, the EVM value was about 3.41%, which satisfies the 3GPP specification. In addition, control signals were found to be demodulated successfully. • We developed an analog radio-over-fiber system capable of analog main signal transmission and remote RRU control on a single wavelength. • The proposed system enables subcarrier multiplexing transmission of the analog main signal and control signal. • The input power balance is designed to avoiding intermodulation distortion. • We successfully transmitted a 256-QAM 5G NR signal and control signal using a system consisting of a 20-km RoF link and mmWave band antenna. [ABSTRACT FROM AUTHOR]

Abstract This article presents an experimental demonstration of a high-capacity millimeter-wave 5G NR signal transmission with analog radio-over-fiber (ARoF) fronthaul over multi-core fiber and full real-time processing. The demonstration validates the core of the blueSPACE fronthaul architecture which combines ARoF fronthaul with space division multiplexing in the optical distribution network to alleviate the fronthaul capacity bottleneck and maintain a centralized radio access network with fully centralized signal processing. The introduction of optical beamforming in the blueSPACE architecture brings true multi-beam transmission and enables full spatial control over the RF signal. The proposed ARoF architecture features a transmitter that generates the ARoF signal and an optical signal carrying a reference local oscillator employed for downconversion at the remote unit from a single RF reference at the central office. A space division multiplexing based radio access network with multi-core fibre allows parallel transport of the uplink ARoF signal and reference local oscillator at the same wavelength over separate cores. A complete description of the real-time signal processing and experimental setup is provided and system performance is evaluated. Transmission of an 800 MHz wide extended 5G NR fronthaul signal over a 7-core fibre is shown with full real-time signal processing, achieving 1.4 Gbit/s with a bit error rate $$

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 14–69 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. [ABSTRACT FROM AUTHOR]

This article presents an experimental demonstration of a high-capacity millimeter-wave 5G NR signal transmission with analog radio-over-fiber (ARoF) fronthaul over multi-core fiber and full real-time processing. The demonstration validates the core of the blueSPACE fronthaul architecture which combines ARoF fronthaul with space division multiplexing in the optical distribution network to alleviate the fronthaul capacity bottleneck and maintain a centralized radio access network with fully centralized signal processing. The introduction of optical beamforming in the blueSPACE architecture brings true multi-beam transmission and enables full spatial control over the RF signal. The proposed ARoF architecture features a transmitter that generates the ARoF signal and an optical signal carrying a reference local oscillator employed for downconversion at the remote unit from a single RF reference at the central office. A space division multiplexing based radio access network with multi-core fibre allows parallel transport of the uplink ARoF signal and reference local oscillator at the same wavelength over separate cores. A complete description of the real-time signal processing and experimental setup is provided and system performance is evaluated. Transmission of an 800 MHz wide extended 5G NR fronthaul signal over a 7-core fibre is shown with full real-time signal processing, achieving 1.4 Gbit/s with a bit error rate < 3.8 × 10 - 3 and thus below the limit for hard-decision forward error correction with 7% overhead. [ABSTRACT FROM AUTHOR]

Towards relieving the bandwidth limitations in 5G mobile fronthaul networks, a Fiber Wireless (FiWi) small cell architecture is presented, relying on spectrally efficient analog transport on intermediate frequency over fiber (IFoF) and a millimeter wave (mmWave) phased array antenna (PAA) interfaced with a low-loss optical add/drop multiplexer (OADM) on Si3N4/SiO2 TriPleX platform with 5 dB fiber-to-fiber losses. Specifically, four 1 Gb/s FiWi links, each carrying a 250 MBd 16-QAM signal on 5.8 GHz IFoF, are wavelength division multiplexed (WDM) and transported across a 10 km Single Mode Fiber (SMF), before being demultiplexed into the constituent channels in the OADM device and subsequently wirelessly transmitted by the PAA over a 1 m-long V-band link with 90° degree beamsteering capability. Featuring 4x 1Gb/s user rate with beamsteering to meet the respective 5G key performance indicator (KPI) for the peak user rate and an EVM within the acceptable 3GPP limit of 12.5%, the current work forms the first centralized FiWi point-to-multipoint small cell architecture with efficient transport scheme on IFoF and ubiquitous 360°-degree coverage for emerging 5G mmWave networks. [ABSTRACT FROM AUTHOR]

Towards the 5G millimeter Wave (mmWave) era, analog transport offers a spectrally efficient scheme for converged Fiber Wireless (FiWi) networks. Signal integrity is traditionally considered as a limiting factor due to various non-linearities attributed to the microwave photonic link, expected to be further exacerbated by the RF-chain of beamforming Phased Array Antennas (PAAs). The letter proposes the end-to-end evaluation of FiWi analog links as unified communication channels rather than separately for the radio or optical part, presenting a link with a 32-element 60 GHz PAA, 1 m V-band distance, 10 km fiber and 10 dB dynamic range. The measurements reveal a third order Intercept Point (IIP3) of 4.8 dBm, compared to 22.8 dBm exclusively for the optics, pinpointing the V-band radio as the main source of degradation rather than the microwave photonic link. Single user uplink is also benchmarked using 300 Mbd QPSK, 250 16-QAM and 100 Mbd 32-QAM, achieving data-rate up to 1 Gb/s and beamsteering of 120° degrees. [ABSTRACT FROM AUTHOR]

The introduction of millimeter wave (mm-wave) frequency bands for cellular communications with significantly larger bandwidths compared to their sub-6 GHz counterparts, the resulting densification of network deployments and the introduction of antenna arrays with beamforming result in major increases in fronthaul capacity required for 5G networks. As a result, a radical re-design of the radio access network is required since traditional fronthaul technologies are not scaleable. In this article the use of analog radio-over-fiber (ARoF) is proposed and demonstrated as a viable alternative which, combined with space division multiplexing in the optical distribution network as well as photonic integration of the required transceivers, shows a path to a scaleable fronthaul solution for 5G. The trade-off between digitized and analog fronthaul is discussed and the ARoF architecture proposed by blueSPACE is introduced. Two options for the generation of ARoF two-tone signals for mm-wave generation via optical heterodyning are discussed in detail, including designs for the implementation in photonic integrated circuits as well as measurements of their phase noise performance. The proposed photonic integrated circuit designs include the use of both InP and SiN platforms for ARoF signal generation and optical beamforming respectively, proposing a joint design that allows for true multi-beam transmission from a single antenna array. Phase noise measurements based on laboratory implementations of ARoF generation based on a Mach–Zehnder modulator with suppressed carrier and with an optical phase-locked loop are presented and the suitability of these transmitters is evaluated though phase noise simulations. Finally, the viability of the proposed ARoF fronthaul architecture for the transport of high-bandwidth mm-wave 5G signals is proven with the successful implementation of a real-time transmission link based on an ARoF baseband unit with full real-time processing of extended 5G new radio signals with 800 MHz bandwidth, achieving transmission over 10 km of 7-core single-mode multi-core fiber and 9 m mm-wave wireless at 25.5 GHz with bit error rates below the limit for a 7% overhead hard decision forward error correction. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a multi-user Fiber Wireless IFoF/mmWave uplink comprising a 32-element 60 GHz Phased Array Antenna (PAA) and 10 km of fiber for 5G fronthaul networks, supporting beamsteering within a 120° sector and 0.6 Gb/s uplink capacity within a 5 dB bandwidth of 2 GHz. The flexibility of the link is highlighted in two 3-user scenarios with 0.6 Gb/s uplink traffic: A Frequency Division Multiplexing (FDM) scheme with the PAA receiving isotropically at different frequencies and a Spatial Division Multiplexing (SDM) scheme where the same V-band frequency is re-used by all three users but are selectively received by the PAA using beamsteering. Error-free transmission with 100 Mbaud QPSK per user is demonstrated for both cases, forming the first comparison of FDM and SDM towards multi-user 5G mmWave/IFoF networks. [ABSTRACT FROM AUTHOR]

A Wavelength Division Multiplexing (WDM)-enabled analog mobile fronthaul architecture is presented supporting enhanced flexibility by exploiting the fine filtering properties of a fully reconfigurable, silicon photonics-based filtering element. Numerical studies are presented emphasizing on the flexibility, low-energy consumption, and the compatibility of our proposed chip-scale implementations with the analog Radio over Fiber (RoF)-based mobile transport. Proof-of-concept analog photonic processing of 1 Gbaud Quadrature Phase Shift Keying (QPSK)-modulated radio is successfully demonstrated through RoF transmission experiments. The integration of the analog mobile fronthauling segment in a WDM-enabled, Reconfigurable Optical Add/Drop Multiplexers (ROADM)-assisted fronthaul/midhaul infrastructure supporting low-latency edge computing is also discussed. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a multiband intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless mobile fronthaul link for gigabit capacity over the unlicensed V-band (57–64 GHz). Digital synthesis of the multiband radio waveforms is performed at the baseband unit using digital subcarrier multiplexing technique, whereas digital predistortion is exploited to cope with the analog IFoF channel impairments without any further baseband processing at the digital-free remote radio head. Commercial optoelectronic components and analog V-band radio and antenna equipment for 7-km fiber and 5-m wireless transmission are employed to successfully demonstrate both uplink and downlink connectivity. An aggregate capacity up to 24 Gb/s was demonstrated with a 6-band 1 Gbaud 16-QAM on a 7.2-GHz analog bandwidth over the combined fiber/wireless channel showing error vector magnitude (EVM) values below the 3GPP requirements (<12.5%) for 5G systems. Multiformat assignment on each subcarrier was also realized by using M-PSK and 16-QAM schemes to achieve 18-Gb/s connectivity for both uplink and downlink, while demonstrating flexible resource allocation capabilities. By replacing the stand-alone optical modulator with an InP-based externally modulated laser chip for the implementation of the IFoF transmitter, a 16-Gb/s aggregate capacity was showcased on a 7-km fiber link and 5-m wireless channel with a 4-band 16-QAM encoded at 1 Gbaud. Successful operation with robust EVM performance was demonstrated using also the 6-band scheme of 1 Gbaud QPSK bands. [ABSTRACT FROM AUTHOR]

WDM-PON has been considered a promising solution for future fronthaul links concerning new mobile networks applications. However, in order to avoid inventory problems and reduce operation costs, there is a need for colorless sources, where the same basic optical source can be used regardless of the desired wavelength. Also, the digital RoF scheme, which has been employed so far, might require a bandwidth that is prohibitive even for optical fiber links. In this paper, we propose and numerically investigate a bidirectional colorless WDM-PON fronthaul transporting analog RoF signals as an alternative to meet these demands. All simulations were performed using a framework calibrated with experimental data. For the downstream, we employ a double-cavity self-seeding technique, while the upstream is performed by a cascaded-RSOAs carrier-reuse approach. BER and EVM simulation analysis are presented for various data rates, modulations formats and RF bands ranging from 1 to 5 GHz, demonstrating the feasibility of our proposed topology as a novel fronthaul approach. [ABSTRACT FROM AUTHOR]

With the continuously increasing demand of cost effective, broadband wireless access, radio-over-fiber (RoF) starts to gain more and more momentum. Various techniques already exist, using analog (ARoF) or digitized (DRoF) radio signals over fiber; each with their own advantages and disadvantages. By transmitting a sigma delta modulated signal over fiber (SDoF), a similar immunity to impairments as DRoF can be obtained while maintaining the low complexity of ARoF. This letter describes a detailed experimental comparison between ARoF and SDoF that quantifies the improvement in linearity and error vector magnitude (EVM) of SDoF over ARoF. The experiments were carried out using a 16-QAM constellation with a baudrate from 20 to 125 MBd modulated on a central carrier frequency of 1 GHz. The sigma delta modulator runs at 8 or 13.5 Gbps. A high-speed vertical-cavity surface-emitting laser (VCSEL) operating at 850 nm is used to transmit the signal over 200-m multimode fiber. The receiver amplifies the electrical signals and subsequently filters to recover the original RF signal. Compared with ARoF, improvements exceeding 40 dB were measured on the third order intermodulation products when SDoF was employed, the EVM improves between 2.4 and 7.1 dB. [ABSTRACT FROM PUBLISHER]

• The paper proposes a new topology for a B5G WDM-PON fronthaul. • The topology employs tunable VCSELs as colorless sources for downstream transmission, as well as data erasure and wavelength reuse for upstream. • Radio-over-fiber transmission performance is evaluated for 1.25 Gbps at the RF carrier frequency of 3.5 GHz and 10 Gbps at 26 GHz, over a 20 km optical link. • The simulation setup is validated by direct comparison against available experimental data.The results comply to 3GPP requirements. The 5G/6G fronthaul link is one of the main drivers for the rising of new passive optical network (PON) standards. Among the possible technologies, wavelength division multiplexing (WDM) is likely the most suitable to meet the stringent performance requirements of fronthaul applications. However, to reduce the implementation and operation costs of WDM-PONs, one of the main issues is the availability of colorless optical sources, in which the same optical hardware can be used to generate any wavelength required by the network. In order to address these needs, in this paper, we propose and analyze a bidirectional colorless WDM-PON topology serving as an analog fronthaul for a 5G and Beyond scenario, comprising the use of recently demonstrated tunable VCSEL lasers for the downlink and the carrier reuse technique for the uplink. We numerically evaluated radio-over-fiber transmission performance when transmitting 1.25 Gbps at the RF carrier frequency of 3.5 GHz and 10 Gbps at the RF carrier frequency of 26 GHz, over a 20 km optical link. The simulation setup is validated by direct comparison against available experimental results, and the obtained results fall within the 3GPP requirements, demonstrating that the proposed topology is a suitable candidate for a future fronthaul configuration. [ABSTRACT FROM AUTHOR]

Radio-over-Fiber (RoF)-based cellular backhauling consitutes a promising solution to realize a cost-effective evolution of radio access networks towards higher radio-cells densification. In this paper, we recall the main characteristics of an innovative cellular backhauling all-optical network architecture called Generic Radio-over-Fiber Access Network (GeRoFAN) aiming to federate 4G system radio cells. However, the transport of multiple radio channels over an analog RoF link is subject to optical crosstalk and intermodulation distortions causing a decrease of the wireless system capacity. Supported by an analytical modeling of the relevant optical transmission limitations, we propose an impairment-aware radio cellular backhauling strategy for GeRoFAN able to maximize the radio cellular capacity while achieving an efficient use of optical resources. This optimization problem is solved through Pareto-based Genetic Optimization (PaGeO), a multi-objective meta-heuristic based on evolutionary algorithms and exploiting the concept of Pareto front. Numerical results indicate that PaGeO, applied to LTE cellular system, outperforms alternative backhauling strategies by achieving an excellent compromise between preserving the radio capacity of the system and the number of required optical channels. We also highlight how the optimal backhauling strategy calculated using PaGeO enables GeRoFAN to take full benefit from overlaying several radio channels per cell site. [ABSTRACT FROM AUTHOR]

Abstract WDM-PON has been considered a promising solution for future fronthaul links concerning new mobile networks applications. However, in order to avoid inventory problems and reduce operation costs, there is a need for colorless sources, where the same basic optical source can be used regardless of the desired wavelength. Also, the digital RoF scheme, which has been employed so far, might require a bandwidth that is prohibitive even for optical fiber links. In this paper, we propose and numerically investigate a bidirectional colorless WDM-PON fronthaul transporting analog RoF signals as an alternative to meet these demands. All simulations were performed using a framework calibrated with experimental data. For the downstream, we employ a double-cavity self-seeding technique, while the upstream is performed by a cascaded-RSOAs carrier-reuse approach. BER and EVM simulation analysis are presented for various data rates, modulations formats and RF bands ranging from 1 to 5 GHz, demonstrating the feasibility of our proposed topology as a novel fronthaul approach.