Radio Over Fiber Technique Research Articles

High-speed reach-extended IM-DD system with low-complexity DSP for 6G fronthaul [Invited

With the rising traffic demand from the metaverse, holographic communications, and so on, in beyond-5G (B5G)/6G cloud radio access networks (C-RANs), fronthaul (FH) networks that transport radio information between antennas and distributed/central units will become increasingly demanding. Optical technologies are indispensable in supporting 6G FH deployment, which needs to be high-speed and power/cost-effective simultaneously; low latency is also crucial. This work is extended from our invited paper at OFC2023. While the conference version focused on the wired-wireless conversion/converging side [e.g., using digital signal processing (DSP)-enhanced radio-over-fiber (RoF) techniques] of FH, this work contributes to the complementary side, i.e., optical transmission techniques. Considering 6G capacity and cost requirements, beyond-200-Gb/s/λ optics based on intensity-modulation direct-detection (IM-DD) PAM4 and low-complexity DSP are targeted, which transparently support digital RoF techniques like analog-to-digital-compression (ADX)-RoF (split Option 8) or Delta-sigma RoF, and other functional split options. On the other hand, while the reach of 5G FH may be around 10 km, in 6G FH routing and/or rural connectivity cases, distance can be extended to 20 km or even 40 km. In these scenarios, fiber dispersion in the C-band and even edge wavelengths of the O-band pose a significant challenge for the reach extension of 200G IM-DD systems. We validate through extensive experiments the efficient FH reach extension and dispersion mitigation based on a low-complexity optoelectronic feedforward equalization (OE-FFE) technique. We experimentally verify 224 Gb/s single-wavelength and dense WDM transmissions over up to 41 km distances in the challenging C-band with lean digital equalizers and hard-decision forward error correction (HD-FEC), which are among the first demonstrations to our knowledge. Even with split Option 8 and extended reach, the FH systems support up to a 10 Tb/s Common Public Radio Interface (CPRI)-equivalent rate and >300Gb/s peak wireless data rate. The presented systems can be useful for high-capacity, reach-extended FH scenarios toward 6G.

DSP-enhanced radio-over-fiber technologies for 5G-and-beyond wired-wireless convergence

Wired-wireless convergence is considered one of the most promising concepts for the access networks in the upcoming beyond-5G era, a notable example being the radio-over-fiber (RoF) technology that delivers broadband wireless data from/to the edge cloud to/from the antenna sites seamlessly. For future radio access, the capacity, latency, and fidelity requirements pose great challenges to the RoF schemes. With the advances of field-programmable gate arrays, application specific integrated circuits, and high-speed data converters, in recent years, digital signal processing (DSP) has been able to play an increasingly important role in RoF system/processing. Such an analog-digital coordinated scheme, namely, DSP-enhanced RoF, has merits in flexibility, parallelized processing capability, and robustness. This paper aims to provide comprehensive analysis of three major DSP-enhanced RoF techniques, namely, DSP-based intermediate-frequency over fiber, analog-to-digital compression RoF, and delta-sigma RoF. Besides performance, quantitative and qualitative analysis will be presented on latency, power consumption, and system complexity, attributes that are important in practice. In addition, we will discuss the challenges to and opportunities for future research.

Total Cost of Ownership of Digital vs. Analog Radio-Over-Fiber Architectures for 5G Fronthauling

The article analyzes the total cost of ownership (TCO) of 5G fronthauling solutions based on analog and digital radio-over-fiber (RoF) architectures in cloud radio access networks (C-RANs). The capital and operational expenditures (CAPEX, OPEX) are assessed, for a 10-year period, considering three different RoF techniques: intermediate frequency analog RoF (IF-A-RoF), digital signal processing (DSP) assisted analog RoF (DSP-A-RoF), and digital RoF (D-RoF) based on the common public radio interface (CPRI) specifications. The greenfield deployment scenario under exam includes both fiber trenching (FT) and fiber leasing (FL) options. The TCO is assessed while varying (i) the number of aggregated subcarriers, (ii) the number of three-sector antennas located at the base station, and (iii) the mean fiber-hop length. The comparison highlights the significance that subcarrier aggregation has on the cost efficiency of the analog RoF solutions. In addition, the analysis details the contribution of each cost category to the overall CAPEX and OPEX values. The obtained results indicate that subcarrier aggregation via DSP results in high cost efficiency for a mobile fronthaul network, while a CPRI-based architecture together with FL brings the highest OPEX value.

64-GHz millimeter-wave photonic generation with a feasible radio over fiber system

A full-duplex radio over fiber (RoF) link with the generation of a 64-GHz millimeter wave (mm-wave) is investigated. This system is proposed as a solution to cope with the demands of a multi-Gb/s data transmission in the fifth generation (5G) and beyond for small cell networks. Cost reduction and performance improvement are achieved by simplifying the mm-wave generation method with an RoF technique. High-frequency radio signals are considered challenging in the electrical generation domain; therefore, our photonic generation method is introduced and examined. RoF design is proposed for mm-wave generation using both phase modulation and the effect of stimulated Brillouin scattering in the optical fiber for the first time. RoF system with transmission rates of 5 Gb/s is successfully achieved. In our scheme, one laser source is utilized and a fiber Bragg grating is used for wavelength reuse for the uplink connection. Stable mm-wave RoF link is successfully achieved in up to a 100-km fiber link length with high quality carrier. Simulation results show a reduction in fiber nonlinearity effects and the mm-wave signal has low noise equal to −75 dBm. This study ensures a practical mm-wave RoF link, and it could be appropriate for small cell 5G networks by reducing the installation cost.

Performance Improvement and Cost Reduction Techniques for Radio Over Fiber Communications

Advanced cost reduction and performance improvement techniques conceived for Radio Over Fiber (ROF) communications are considered. ROF techniques are expected to form the backbone of the future fifth generation of wireless networks. The achievable link performance and the associated deployment cost constitute the most salient metrics of an ROF architecture. In this paper, we commence by providing a rudimentary overview of the ROF architecture, and then we elaborate on ROF techniques designed for improving the attainable system performance. We conclude by describing the ROF techniques conceived for reducing the ROF system installation costs.

Real-time dual-band wireless videos in millimeter-wave radio-over-fiber system

A dual-band converged radio-over-fiber (RoF) access system at 60-GHz and 100-GHz millimeter-wave (mm-wave) is proposed. Real-time end-to-end delivery of two channels of independent high-definition (HD) video services simultaneously carried on 60-GHz and 100-GHz radios is demonstrated for the first time. PRBS data transmission with equivalent data rate and format is also tested to characterize the system performance. The analysis of the spectrum from the beating signal indicates the entire 60-GHz band and the W-band can be retrieved without interference. The real-time HD video display and error-free (BER<10–9) data transmission demonstrate the feasibility of the proposed wireless access system using converged fiber-optic and mm-wave RoF techniques.

Stable radio frequency phase delivery by rapid and endless post error cancellation

We propose and demonstrate a phase stabilization method for transfer and downconvert radio frequency (RF) signal from remote antenna to center station via a radio-over-fiber (ROF) link. Different from previous phase-locking-loop-based schemes, we post-correct any phase fluctuation by mixing during the downconversion process at the center station. A rapid and endless operation is predicted. The ROF technique transfers the received RF signal directly, which will reduce the electronic complexity at the antenna end. The proposed scheme is experimentally demonstrated, with a phase fluctuation compression factor of about 200. The theory and performance are also discussed.

Digitized RF-over-fiber as a cost-effective and energy-efficient backhaul option for wireless communications

Digitized RF-over-fiber technique based on bandpass sampling theory is studied as an alternative of analog radio-over-fiber to deliver wireless signals, taking advantage of digital optical link and realizing simpler base station architecture. In this paper, we present an overview of our recent research on digitized radio-over-fiber (RoF) technique, including discussions on the designing issues and possible solutions, proof-of-concept demonstrations and experimental results. Then, we examine the energy efficiency of the digitized RoF technique using a generic base station (BS) power model and compare with conventional BS designs. Based on the estimated energy consumption per square meter, digitized RoF technique has advantage for larger cell size.

Challenges to radio over fiber (RoF) technology and its mitigation schemes – A review

For realization of future high performance integrated networks, broadband distribution and access networks and to meet the increasing demand of multimedia services with a guaranteed quality of service, RoF technology comes out as the most promising technology that combines the capacity of optical networks with the flexibility and mobility of wireless networks. Reduction in complexity at the antenna site, reduction in installation cost of access networks, possibility of dynamically allocation of radio carriers to different antenna sites, transparency and scalability are the few advantages of radio-over-fiber (RoF) technology. In this paper, we review the different challenges that limit the probable capabilities of RoF communication networks and different mitigation techniques to combat with these challenges to realize high-performance RoF links.