Analog RoF Research Articles

Optical continuous pulse position modulation-based analog RoF via frequency-domain position estimation.

Analog radio-over-fiber (A-RoF) solutions for mobile fronthaul are regaining wide attention due to their high spectral efficiency and low complexity. However, the performance of A-RoF is usually limited by the fiber link fidelity. In this Letter, we propose and experimentally demonstrate an optical continuous pulse position modulation-based analog radio-over-fiber (OCPPM-RoF) scheme, in which the amplitudes of wireless waveforms are mapped to the time-domain positions of optical pulses to decouple the additive noise. The de-modulation of OCPPM-RoF signals is performed by a frequency-domain continuous position estimation (FD-CPE) algorithm including cross-power spectrum calculation and weighted least square for accurate delay estimation. In the experiment, by adopting appropriate pulse width factors, the recovered signal-to-noise ratio (SNR) can be flexibly adjusted within a wide range from 31.8 to 54.0 dB, supporting the transmission of various formats from 256-QAM to 65536-QAM. The results indicate that OCPPM-RoF can be a promising candidate for future fronthaul.

Experimental results of multiplexing transmission of 256-QAM 5G NR signal with control signal by SCM over 20-km analog RoF link

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.

Power Over Fiber and Analog Radio Over Fiber Simultaneous Transmission Over Long Distance in Single Mode, Multicore, and Hollow Core Fibers

AbstractIn this work, a novel study of the feasibility of shared Power over Fiber (PoF) and Fifth‐Generation (5G) New Radio (NR) Analog Radio over Fiber (ARoF) over long distance Hollow‐core Fibers (HCF) is presented. Comparative measurements between similar lengths of HCFs, Multicore (MCF) and Single Mode Fibers (SMF) are performed. A complete analysis on the Stimulated Raman Scattering (SRS)‐induced noise transfer from PoF to ARoF is tackled. Relative Intensity Noise (RIN) of ARoF signals is measured for all the optical fibers tested, observing no degradation in HCFs, neither on MCFs and significant deterioration in SMFs. A combination of PoF and 5G NR ARoF link in a single fiber is implemented, and 5G NR signals with different modulation formats are successfully transmitted through HCFs and MCFs without degradation, while SRS‐induced noise transfer in SMFs massively deteriorate them. PoF transmission efficiencies are also analyzed, achieving up to 9.9 % System Energy Efficiency (SEE) for a 3.1 km HCF, 0.9 % for a 11.1 km HCF and 1.5 %, 13.5 %, and 20.4 % in a 10 km MCF, a 9.8 km SMF and a 3.3 km SMF, respectively. The PoF signal is used to supply a Bluetooth Low‐Energy (BLE) load with a power consumption of 20 mW.

Transmission of 10 Gbps C-band-signal-based Radio Over Fiber for Next Generation Communication Systems

Rapid development of 5G networks encourages researchers to improve the radio-over-fiber (RoF) technique in order to reach 10 Gbps data transmission rates, to increase bandwidth and range, while reducing latency and implementation cost. This paper evaluates an analog radio-over-fiber (ARoF) technique that is compatible with long-distance communication systems. We demonstrate a long distance transmission of a 28 GHz 64 QAM signal via a single mode fiber (SMF) after modulating it with the use of two parallel Mach-Zehnder modulators, without any optical amplifiers. The results show that our prototype solution is capable of transferring data over distances of up to 140 km, via SMF, with a 10 Gbps data rate. The error vector magnitude (EVM) was found to be 7.709%. The proposed system offers exceptional capabilities in terms of supporting high bitrates, while ensuring that EVM remains within the 3GPP limits. Compared to other works, the proposed solution proves to be superior in terms of performance, making it an ideal choice for next generation long-haul communication systems.

An overview of recent studies on the limitations of semiconductor lasers under direct modulation for use in analog RoF systems

An overview of recent studies on the limitations of semiconductor lasers under direct modulation for use in analog RoF systems

A Novel A-RoF and VLC-based Full-Duplex FiWi System for B5G Applications

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 (EVMRMS), 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.

Beam Control Method for Analog RoF Systems Based on Pre-Beamforming with a Few Antenna Elements

Beam Control Method for Analog RoF Systems Based on Pre-Beamforming with a Few Antenna Elements

SNR improved digital-cascaded-pulse-code-modulation radio-over-fiber scheme supporting 16,777,216 QAM for mobile fronthaul

We propose a digital-cascaded-pulse-code-modulation radio-over-fiber (DCP-RoF) scheme and verify it experimentally in a coherent transmission system. The 50-Gbaud 2-order 6-bit DCP-RoF signal with a common public radio interface equivalent data rate of 279Gb/s/λ is successfully transmitted in a 10-km standard single-mode fiber link. Results show that the 2-order 6-bit DCP-RoF scheme achieves a maximum recovered signal-to-noise ratio (SNR) of 83.43 dB, which meets the requirements for 16,777,216-quadrature-amplitude-modulation (16,777,216-QAM) transmission. The DCP-RoF scheme has advantages over analog RoF and digital–analog RoF in terms of SNR improvement, as well as advantages over digital RoF (D-RoF) in spectral efficiency. Furthermore, an average SNR enhancement of 13.48 dB for each linearly increased bandwidth is achieved in the DCP-RoF scheme. Our work suggests many optimistic possibilities for the future radio access networks and mobile fronthaul.

40-GHz Band Photodiode-Integrated Phased Array Antenna Module for Analog-Radio over Fiber toward Beyond 5G

In 5th generation (5G) and Beyond 5G mobile communication systems, it is expected that numerous antennas will be densely deployed to realize ultra-broadband communication and uniform coverage. However, as the number of antennas increases, total power consumption of all antennas will also increase, which leads to a negative impact on the environment and operating costs of telecommunication operators. Thus, it is necessary to simplify an antenna structure to suppress the power consumption of each antenna. On the other hand, as a way to realize ultra-broadband communication, millimeter waves will be utilized because they can transmit signals with a broader bandwidth than lower frequencies. However, since millimeter waves have a large propagation loss, a propagation distance is shorter than that of low frequencies. Therefore, in order to extend the propagation distance, it is necessary to increase an equivalent isotropic radiated power by beamforming with phased array antenna. In this paper, a phased antenna array module in combined with analog radio over fiber (A-RoF) technology for 40-GHz millimeter wave is developed and evaluated for the first time. An 8×8 phased array antenna for 40-GHz millimeter wave with integrated photodiodes and RF chains has been developed, and end-to-end transmission experiment including 20 km A-RoF transmission and 3-m over-the-air transmission from the developed phased array antenna has been conducted. The results showed that the 40-GHz RF signal after the end-to-end transmission satisfied the criteria of 3GPP signal quality requirements within ±50 degrees of main beam direction.

SNR Improved Digital-PCM Radio-Over-Fiber Scheme Supporting 65536 QAM for Mobile Fronthaul

We propose a digital pulse-code-modulation radio-over-fiber (DP-RoF) scheme and verify it experimentally in a 10-km standard single-mode fiber (SSMF) coherent system. The 20-Gbaud DP-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 112 Gb/s is successfully transmitted in the system with excellent performance. The recovered signal-to-noise ratio (SNR) of wireless signal in DP-RoF scheme is 50.14 dB, which is 26.62, 20.01 and 13.28 dB higher than that of analog radio-over-fiber (A-RoF), digital-analog radio-over-fiber (DA-RoF) and digital radio-over-fiber (D-RoF), respectively. The DP-RoF scheme meets the error vector magnitude (EVM) requirement of 65536 quadrature amplitude modulation (QAM), while A-RoF and DA-RoF schemes cannot reach the EVM threshold of 1024 QAM. With improved SNR, the proposed DP-RoF system is a promising scheme for ultra-high-order QAM transmission in future 6G fronthaul.

Low Noise Ultra-Flexible SiP Switching Platform for mmWave OCDM & Multi-Band OFDM ARoF Fronthaul

A highly flexible wavelength and space switched analog radio-over-fiber (ARoF) fronthaul transmission of a millimeter-wave (mmWave) emerging 6G waveform over a centralized/ cloud radio access network (C-RAN) is experimentally demonstrated in this work. A spread spectrum multiplexing technique — orthogonal chirp division multiplexing (OCDM) — which is highly resilient to inter-channel interference and enables enhanced channel estimation is utilized in the fronthaul transmission demonstration. The flexible properties of a low noise silicon photonic (SiP) microring resonator (MRR) based tunable laser and a low cross-talk 4×4 SiP optical wavelength/space switch are combined to form a reconfigurable 10 km fronthaul system enabling 64-QAM OCDM transmission at 24 GHz with consistent performances ~5% EVM across all test wavelengths/ports. A signal constituting Wi-Fi and 5G NR standard compatible 64-QAM orthogonal frequency division multiplexing (OFDM) bands, at 10 GHz and 24 GHz respectively, are also transmitted and evaluated in the proposed system with EVM performances below 64-QAM EVM limit (8%) achieved, thus demonstrating the system’s potential in a future converged multi-service environment.

Multi-frequency 5G NR millimeter-wave signal generation over analog RoF link using optical frequency combs

Optical heterodyne analog radio-over-fiber (A-RoF) links can provide a cost-effective and spectrally efficient solution for the generation and distribution of millimeter-wave/Terahertz (mm-wave/THz) carriers for the next-generation wireless systems. The use of an optical frequency comb (OFC) source in such a system can facilitate carrier generation free from frequency fluctuation. However, decorrelation between tones, due to path length difference, can lead to phase noise on the generated mm-wave carrier — limiting the performance of low subcarrier spacing multi-carrier signals specified in the 5G standard. In this work, we analyze the effect of comb tones decorrelation due to path length difference on the performance of 5G compatible 244 kHz subcarrier spacing 59 GHz OFDM signal over an optical heterodyne A-RoF link using a gain switched laser (GSL) OFC source. Furthermore, we demonstrate the ability of the OFC-based A-RoF optical/mm-wave system to support flexible and interoperable mm-wave functionality through signal generation at 27 GHz, 43 GHz and 59 GHz using different pairs of GSL OFC tones for remote heterodyning. The capability of multi-frequency 5G NR compatible mm-wave signal generation and potential for photonic integration make the demonstrated GSL OFC based optical heterodyne A-RoF system a suitable candidate for deployment in the next generation wireless systems.

Towards optimization of 5G NR transport over fiber links performance in 5G Multi-band Networks: An OMSA model approach

The application of analog radio over fiber (A-RoF) systems for 5G new radio (NR) multiband waveforms presents challenges, including nonlinearity introduced by the Mach Zehnder Modulator and the dispersion and attenuation of the optical signal over long fiber lengths. To address these challenges, this paper proposes a new version of the magnitude-selective affine (MSA) model, named the optimized magnitude-selective affine (OMSA) model, which incorporates a power-reliant weighting function to improve performance while reducing complexity via Digital Predistortion (DPD). The OMSA model is tested using 5G NR signals at 10 GHz with 50 MHz and flexible-waveform signals at 2.14 GHz with a 20 MHz bandwidth, transmitted over a 10 km fiber length using a Mach Zehnder Modulator and a 1550 nm optical carrier. The performance of the OMSA model is compared to the MSA and generalized memory polynomial (GMP) models in terms of adjacent channel power ratio, error vector magnitude, and complexity. The results show that the OMSA model outperforms the MSA and GMP models in terms of performance reducing the error vector magnitude to 1.9% as compared to 4% and 3% in case of GMP and MSA respectively. Additionally, in terms of complexity measured via coefficients, OMSA is 168 times more efficient as compared to GMP and offers 1.93 times higher efficiency as compared to MSA while maintaining lower complexity. The experimental demonstration of 5G NR multiband waveforms over A-RoF links using the OMSA model represents a significant step towards the practical implementation of high-performance, low-complexity 5G NR systems over fiber-optic links and provides a promising solution to the challenges associated with DPD linearization for A-RoF systems.

Demonstration of High Capacity Bidirectional A-RoF System Using Wavelength Reuse and Frequency Multiplexing

We demonstrate a practical wavelength reuse bidirectional analog radio-over-fiber (A-RoF) system served by a single distributed feedback (DFB) laser. Frequency interleaving of downlink and uplink signals is proposed to ameliorate the spectral efficiency and mitigate the interference raised by the bidirectional transmission. Pre-emphasis is exploited to counteract the performance impairment brought about by the interaction between laser chirp and fiber chromatic dispersion. Through employing 64-QAM modulated 16 bands and 16-QAM modulated 12 bands filtered orthogonal frequency division multiplexing (f-OFDM) signals with 200 MHz bandwidth, asymmetric transmission with superior flexibility over 25 km fiber is attained, with an aggregate capacity of 20 Gb/s for downlink and 10 Gb/s for uplink. The mutual interference between the downlink and uplink is explored by overlapping the downlink and uplink signal spectra to varying degrees. Using the optimum frequency configuration, system performance is evaluated in terms of EVM and phase noise. To further investigate the effects caused by the Rayleigh backscattering and the stimulated Brillouin scattering (SBS), simulations are conducted on the proposed architecture, validating the conclusion from the experiment that the bidirectional transmission is primarily limited by the Rayleigh backscattering than the stimulated Brillouin scattering.

TL-ANN Based Nonlinear Equalization for Multi-Users Radio Over Fiber System

To mitigate nonlinear distortions in multi-user analog radio over fiber (A-RoF) system, a nonlinear equalizer (NLE) which combines transfer learning (TL) and waveform regression-based artificial neural network (ANN) is proposed and validated experimentally in this research. Unlike traditional ANNs, waveform regression ANNs can be regarded as waveform training ANNs and avoid complex-value training. In this paper, we first analyze the modulation distortions that appear in multi-user RoF systems and then propose a waveform regression ANN-based nonlinear equalizer (ANN-NLE). Subsequently, we use TL to reduce training costs and increase the compatibility of the ANN-NLE. Finally, an A-RoF system with multicore fiber is adopted to verify the proposed approach. According to the simulation and experimental results, the bit error ratio (BER) of a multi-user signal is decreased to the threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , and the improved optical receiver sensitivity is greater than 1.5 dB. This proposed method could realize nonlinear equalization and display good compatibility with different systems.

Demonstration of a hybrid A-RoF/VLC system for beyond 5G applications.

This work reports the implementation of a fiber-optics and visible light communication (VLC)-based flexible optical distribution network for beyond the fifth generation of mobile networks (B5G) applications. The proposed hybrid architecture is composed of a 12.5-km single-mode fiber fronthaul based on the analog radio-over-fiber (A-RoF) technology, followed by a red, green, and blue (RGB)-based VLC link of 1.2 m. As a proof of concept, we experimentally demonstrate a successful deployment of a 5G hybrid A-RoF/VLC system without using pre-/post-equalization, digital pre-distortion, or individual filters for each color, by means of using a dichroic cube filter at the receiver side. The system performance is evaluated in terms of the root mean square error vector magnitude (E V M R M S ), in accordance with the 3rd Generation Partnership Project requirements, and as a function of the light-emitting diodes' injected electrical power and signal bandwidth.

A new full-duplex analog RoF transmission system for 5G/5G+ broadband mobile communication

Abstract A new cost-effective mobile fronthaul architecture has been proposed by designing promising analog radio over fiber (ARoF) transmission system compliant with the next generation ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON). It is conceived for standalone 5G/5G+ mobile communication systems driven by broadband multi-input multi-output (MIMO) millimeter wave data signals using two high spectral efficient modulations. The feasibility of the proposed system was firstly proven in terms of spectral tracing supported by theoretical analysis that disclosed good agreement. Furthermore, the obtained simulation results regarding the system performance evaluation after 22 km bidirectional optical fiber links were revealed high reliable characteristics including error-free transmissions at low receiver sensitivities, and measured power penalties less than 1 dB. In addition, the recovered eye diagrams maintained wide openings with high-quality patterns.

Experimental demonstration of transport over fiber using 5G NR with performance enhancement using DPD

The article proposes an experimental implementation with a performance comparison of 5G new radio (NR) multiband waveforms utilizing analog radio over fiber (A-RoF) link equipped with performance enhancement via digital predistortion (DPD) methods. An unprecedented convolutional neural network (CNN) is compared with our earlier proposed robust methods such as deep neural network (DNN), magnitude-selective affine (MSA) and generalized memory polynomial (GMP) methods. In circumstances when deep learning is not practicable due to high complexity, we have presented an integrative lightweight convolutional neural network (ILWCNN) approach which is stable over time without the need for DPD coefficient updates. The experimental bench consists of a multiband 5G NR standard at a carrier frequency of 20 GHz with a bandwidth of 50 MHz and a flexible-waveform signal at 3 GHz with a bandwidth of 20 MHz. A 10 km of single-mode fiber is used to transport the signals modulated by a dual-drive Mach Zehnder Modulator. The paper discusses the selection of reduced complexity and robust performance of the ILWCNN-based DPD that eventually outperforms the conventional methods. The proposed ILWCNN reduces the error vector magnitude (EVM) to 1.65% as compared to 4.1%, 3.1%, 1.9% and 7.4% of EVM for GMP, MSA, DNN and non-compensated cases respectively. Similarly, the adjacent channel leakage ratio (ACLR) of −28 dBc uncompensated link is reduced with GMP, MSA and ILWCNN to −40 dBc, −45 dBc and −47 dBc respectively. The suggested ILWCNN approach outperforms the compared methods in terms of ACLR and EVM attaining the 3GPP Release 17 requirements.

Bidirectional WDM Multi-Nodes Analog Radio-Over-Fiber Mobile Fronthaul Link Enhanced by Photonic Integrated Devices

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 (<4.5-dB) and low crosstalk (<−20.4-dB), to achieve a high-density WDM system. In the distributed field experiments, we have successfully demonstrated a bidirectional A-RoF MFH over 10-km standard single mode fiber, providing an 8×5-Gbit/s 4-quadrature amplitude modulation (QAM) orthogonal frequency division modulation (OFDM) downlink transmission and a 3×12-Gbit/s 16-QAM uplink transmission.

Power-Over-Fiber Impact and Chromatic-Induced Power Fading on 5G NR Signals in Analog RoF

In this work, we investigate the feasibility of optical powering in coexistence with radio transmission using baseband signals with 5G New Radio (5G NR) numerology with different bandwidths (BW) on Analog Radio over Fiber (ARoF) systems with single mode fibers (SMF). We focus on the impact of chromatic dispersion (CD), non-linear effects, High Power Laser (HPL) instabilities and their interactions, performing simulations and experiments. First, without Power over Fiber (PoF), we verify that increasing the BW of the 5G NR baseband signal reduces the CD-induced power fading at the critical RF frequency with the highest extinction and the error-vector magnitude (EVM) of the received 5G NR signal worsens. The CD-induced power fading is 10 dB smaller for 100 MHz versus 10 MHz baseband signal BWs. Then, we experimentally demonstrate the influence of a PoF signal, generated by a Raman HPL, on the transmission of 5G NR signals in a shared scenario with co-transmission of both PoF and data signals. The CD-induced power fading at the critical RF frequency with the highest extinction is 27 dB smaller for 5G NR signal BWs of 10 MHz and 100 MHz respectively when the HPL is set to +33 dBm. This PoF signal enhances the EVM of the received 5G NR signal to values in compliance with the standard while providing an On/Off Raman gain of 12.7 dB at 1552.8 nm data signal in a 14.43 km SMF link. For a 5G NR signal BW of 10 MHz and a RF carrier frequency of 17 GHz, the EVM improves from 31.3% to 11.6% for a HPL power of +33 dBm. For shorter distances such as 100 m, HPL noise transfer does not affect the EVM of data signal.