Abstract
In this paper, we numerically and experimentally present the bandwidth constraints of a cost-effective 5G mobile fronthaul based on a directly-modulated laser for data modulation and a Mach-Zehnder modulator-based optical double sideband with carrier suppression scheme for optical millimeter wave (mmW) signal generation. The effect of chirp, fiber dispersion and a combination of both on different bandwidth M-Quadrature Amplitude Modulation (M-QAM) signals, i.e. M = 4, 16 and 64, at 40 GHz has also been investigated. Simulation results are first carried out to evaluate the impact of higher chirp of the directly-modulated laser on the link performance as a function of modulation format and signal bandwidth. We then experimentally demonstrate the same scheme transmitting M-QAM signals with bandwidths ranging from 50 to 1000 MHz over a 10 km long single mode fiber. Both experimental and simulation results show that larger signal bandwidths lead to higher optical power penalties due to the combined effect with the error vector magnitudes (EVMs), however still satisfying the required limits of 3GPP standard for all QAM signals. Experimental measurements also show the feasibility of including free space optics links in the optical distribution network with no further significant penalties. Finally, a multiband signal (three-band) transmission is demonstrated leading to an increase of the total bitrate with the measured EVMs are well below the EVM requirement.
Highlights
Nowadays, broadband mobile services, such as cloud access, 4K/8K high definition video, augmented virtual reality, online gaming or social networking require the deployment of the 5th generation (5G) mobile communications providing high bandwidth and low latency connectivity [1].Centralized cloud-radio access network (C-RAN) [2] is the preferred architecture for 5G networks due to the centralization of the baseband units (BBU) in a central pool which is connected to the remote radio heads (RRH) by the mobile fronthaul network (MFH)
error vector magnitudes (EVMs) measurements were done after transmission along a hybrid link composed of a 10 km standard single-mode fiber (SSMF) and 1.5 m free space optics (FSO) link showing no significant penalties introduced by the hybrid link (Fig. 11(c))
Insets (a.3), (b.3) and (c.3), correspond to larger bandwidth and show larger degradation, EVM values are kept below the standard EVM limit for all signals having a received optical power at least of 2 dBm
Summary
Centralized cloud-radio access network (C-RAN) [2] is the preferred architecture for 5G networks due to the centralization of the baseband units (BBU) in a central pool which is connected to the remote radio heads (RRH) by the mobile fronthaul network (MFH). Since the BBU pool includes most of the signal processing and the RRH mainly performs RF/baseband conversion, such architecture offers reduced operational and capital expenditure. Analog radio-over-fiber (RoF) approach combined with optical distribution network (ODN) technology offers a scalable and flexible solution with increased spectral efficiency and transmission capacity by using transceivers with a bandwidth of a few Gb/s [5, 6]. The spectral congestion of lower microwave spectral region is the motivation for exploiting higher frequency bands (25-170 GHz) [7, 8, 9, 10], i.e. millimeter wave (mmW) frequencies, which suffer from the VOLUME XX, 2017
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