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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.

This paper presents an experimental demonstration of analog radio-over-fiber (ARoF) fronthaul for high-bandwidth, high-capacity millimeter wave (mm-wave) extended fifth generation mobile network (5G) new radio (NR) signals over an optical distribution network with optical space division multiplexing (SDM). ARoF is shown to alleviate fronthaul capacity bottlenecks, transporting an 800 MHz wide extended 5G NR signal and allowing to maintain full centralization in a centralized radio access network (C-RAN). The proposed ARoF fronthaul architecture features a transmitter that generates the ARoF signal and an optical signal carrying a reference local oscillator (LO) employed for downconversion at the remote unit (RU) from a single radio frequency (RF) reference at the central office (CO). An SDM based RAN with 7-core multi-core fiber (MCF) allows parallel transport of the uplink ARoF signal and reference LO at the same wavelength over separate cores. Transmission of an 800 MHz wide extended 5G NR fronthaul signal over 7-core MCF is shown with full real-time processing, achieving 1.4 Gbit/s with BER

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.