Abstract
Two experimental configurations of a hybrid K-band (25 GHz) microwave photonic link (MPL) are investigated for seamless broadband wireless access networks. Experimental configurations consist of optical fiber, free-space optics (FSO) and radio frequency (RF) wireless channels. We analyze in detail the effects of channel impairments, namely fiber chromatic dispersion, atmospheric turbulence and multipath-induced fading on the transmission performance. In the first configuration, transmission of the 64-quadrature amplitude modulation (QAM) signal with 5, 20 and 50 MHz bandwidths over 5 km standard single-mode fiber (SSMF), 2 m turbulent FSO and 3 m RF wireless channels is investigated. We show that, for QAM with a high bandwidth, the link performance is being affected more by atmospheric turbulence. In the second configuration, the 20 MHz 4/16/64-QAM signals over a 50 km SSMF and 40 m FSO/RF wireless links are successfully transmitted with the measured error vector magnitude (EVM) values of 12, 9 and 7.9%, respectively. It is shown that, for all transmitted microwave vector signals, the bit error rate is lower than the hard-decision forward-error-correction limit of 3.8×10-3. Moreover, an extended FSO link span of 500 m for 25 GHz hybrid MPL with 16-QAM at 10 Gb/s under the weak and strong turbulence regimes is evaluated via simulation analysis to mimic a practical outdoor system.
Highlights
The low-frequency range (< 6 GHz) in the radio frequency (RF) spectrum adopted for broadband wireless access (BWA) networks is overloaded due to the growing use of wireless technologies in recent years [1,2,3]
Recent literature reports a number of microwave photonic link (MPL) schemes with an extended fiber-reach, e.g., 4- and 16-quadrature amplitude modulated (QAM) signals at 2.5 GHz were successfully transmitted over a 25 km of standard single-mode fiber (SSMF) using a coherent receiver and advanced digital signal processing for phase noise cancellation [1]
In configuration A, we focus on the effect of atmospheric turbulence-induced fading on 64-QAM with a variable bandwidth transmitted over the proposed hybrid MPL consisting of 5 km SSMF, 2 m turbulent free-space optics (FSO) and 3 m RF wireless channels
Summary
The low-frequency range (< 6 GHz) in the radio frequency (RF) spectrum adopted for broadband wireless access (BWA) networks is overloaded due to the growing use of wireless technologies in recent years [1,2,3]. In order to increase the network capacity and efficiency as well as offer the users certain unique benefits, the next-generation BWA networks should operate at higher-carrier frequencies i.e., millimeter-wave (MMW) bands. The radio-over-fiber (RoF) or microwave photonic link (MPL) technology operating at the MMW band has recently been investigated as a viable solution for high-capacity networks (i.e., up to 24 Gb/s per lambda) [4,5,6,7] In centralized architectures, these systems use optical fibers (OFs) as the transmission medium to transfer data from the central office to the base stations, where the MMW signal is wirelessly transmitted to the end users. In 2018, we demonstrated 100 MHz 64-QAM transmission at different carrier frequencies of 24–26 GHz using a low-cost directly modulated laser over 2 m turbulent FSO and 3.6 m RF wireless links with the lowest measured EVM of 4.7% [13]. In configuration A, we focus on the effect of atmospheric turbulence-induced fading on 64-QAM with a variable bandwidth transmitted over the proposed hybrid MPL consisting of 5 km SSMF, 2 m turbulent FSO and 3 m RF wireless channels.
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