Abstract
With the rise of 5G and beyond, the ever-increasing data-rates demanded by mobile access are severely challenging the capacity of optical fronthaul networks. Despite its high reliability and ease of deployment, legacy digital radio-over-fiber (RoF) technologies face an upcoming bandwidth bottleneck in the short term. This has motivated a renewed interest in the development of analog RoF alternatives, owing to their high spectral efficiency. However, unlike its digital counterpart, analog RoF transmission requires a highly linear transceiver to guarantee signal fidelity. Typical solutions exploited in recent research works tend to adopt the use of bulky benchtop components, such as directly modulated lasers (DML) and photodiodes. Although this provides a convenient and quick path for proof-of-concept demonstrations, there is still a considerable gap between lab developments and commercial deployment. Most importantly, a key question arises: can analog-RoF transceivers meet the 5G requirements while being competitive in terms of cost and footprint? Following this challenge, in this work we exploit the use of a low-cost commercial off-the-shelf (COTS) small form-factor pluggable (SFP) transceiver, originally designed for digital transmission at 1 Gbps, which is properly adapted towards analog RoF transmission. Bypassing the digital electronics circuitry of the SFP, while keeping the original transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we demonstrate that high-performance 5G-compatible transmission can be performed by reusing the key built-in components of current low-cost SFP-class transceivers. Particularly, we demonstrate error vector magnitude (EVM) performances compatible with 5G 64QAM transmission both at 100MHz and 400MHz. Furthermore, employing a memory polynomial model for digital pre-distortion of the transmitted signal, we achieve 256QAM-compatible performance at 100MHz bandwidth, after 20 km fronthaul transmission.
Highlights
T HE imminent rise of 5G and beyond radio communications, together with the progressive adoption of the centralized radio-access network (C-RAN) architecture [1], is bringing new challenges for optical transceivers
Due to the widespread dissemination of digital communications, the main efforts from the industry rely on developing low-cost packaged digital transceivers, while most analog solutions remain based on costly discrete components, which require further driving/adaptation so that they can be used for research purposes. We address this scarcity of analog RoF solutions, exploiting a workaround to obtain low-cost analog transceivers through the adaptation of a commercial digital small form-factor pluggable (SFP) transceiver to support the analog transmission of 5G signals
We demonstrate that transmission over 20 km single-mode fiber (SMF) does not impose any major impairment on the signal quality, but nonlinear compensation is required to enable reception of a 256QAM signal with error vector magnitude (EVM) below the 3.5% established limit [12]
Summary
T HE imminent rise of 5G and beyond radio communications, together with the progressive adoption of the centralized radio-access network (C-RAN) architecture [1], is bringing new challenges for optical transceivers. A similar calculation for more than 100 antenna modules, a 4-sector device supporting 400 MHz baseband channels would roughly require 10 Tbps, which is equivalent to about 400 optical OOK-DSB-50GHzgrid channels [16] These high-capacity examples clearly expose the critical upscaling issues that are associated with digital fronthauling, which is driving a renewed interest on the development of A-RoF solutions for 5G and beyond. In Figure 3.a, we can identify three key parts of the digital SFP transceiver: i) the transmitter optical sub-assembly (TOSA), which performs electrical-to-optical (E/O) conversion using a directly-modulated laser, ii) the receiver optical sub-assembly (ROSA), which performs optical-to-electrical (O/E) conversion through an amplified photodiode, and iii) the printed circuit board (PCB) that is responsible for electrically driving the TOSA and ROSA components Since these transceivers are designed for digital fiber communications, a set of necessary adaptations are required to enable the transmission of analog optical signals.
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