60 GHz 5G Radio-Over-Fiber Using UF-OFDM With Optical Heterodyning

Abstract

Abstract-A 5G millimeter-wave radio over fibre optical fronthaul system based on optical heterodyning, utilising an externally injected gain switched distributed feedback laser, is successfully demonstrated. Five bands of UF-OFDM are transmitted over 25 km of fibre and a 28 GHz Vivaldi Antenna wireless link. Transmission performance below the 7% FEC limit is achieved with an aggregate total data rate of 4.56 Gb/s.

Gain-Switched Optical Frequency Combs for Future Mobile Radio-Over-Fiber Millimeter-Wave Systems

“…A tunable optical delay line is inserted in the unmodulated tone's path. This is to allow the phase offset between the two optical paths (due to path length difference including the dispersive effect of the SSMF) to be pre-compensated for optimum performance [7], [11], and swept to observe system limitations.…”

“…Li et al [5] employed two freerunning external cavity lasers (ECL) to achieve 60 Gb/s RoF transmission of 64-quadrature amplitude modulation (QAM) data, while Alavi et al [6] presents the use of an extremely low linewidth dual wavelength fibre laser to demonstrate multicarrier RoF transmission suitable for 5G applications. However, the complexities associated with these methods [7] have contributed to the sustained interest in the use of OFCs as an economic and effective optical source enabling mm-wave RoF communications [8]- [11].…”

“…MLLs suffer from large linewidth (MHz range) and mode partition noise which can be imparted to the heterodyne mm-wave signal [14], and, unlike combs generated through gain-switching, they exhibit a fixed free spectral range (FSR) which limits flexibility in the generated mm-wave carrier. Our recent work, [7], has experimentally demonstrated the use of an OFC generated through gain-switching for mm-wave RoF transmission appropriate for 5G applications. It has highlighted the heightened importance of coherence between optical carriers given the relatively low baud rates associated with mobile transmission.…”

“…The work presented in this paper expands on [7] to provide an analysis, in terms of optimum operating conditions and system limitations, on the use of OFCs generated by gain-switching for mobile RoF mm-wave distribution. Our numerical simulations and experimental testbed results encompass key factors associated with optical heterodyning, namely; the impact of optical linewidth, effective path difference and relative intensity noise (RIN).…”

Coverage Extension of Indoor 5G Network Using RoF-Based Distributed Antenna System

“…However, it requires extra circuitries to stabilize the frequency and phase of the generated mmWave signal (at RAU) to the reference clock in the MHU. Although the optical frequency comb could be alternatively employed to generate the frequency-stabilized mmWave at RAU, its phase is still unlocked, and more importantly, it increases the system complexity, making it difficult to manage the system on a long-term basis [15]. In the IFoF, on the other hand, the mobile signal is downconverted to IF-band (e.g., 2 GHz) prior to the fiber-optic transmission.…”