DSP-enhanced radio-over-fiber technologies for 5G-and-beyond wired-wireless convergence

Wired-wireless convergence is considered one of the most promising concepts for the access networks in the upcoming beyond-5G era, a notable example being the radio-over-fiber (RoF) technology that delivers broadband wireless data from/to the edge cloud to/from the antenna sites seamlessly. For future radio access, the capacity, latency, and fidelity requirements pose great challenges to the RoF schemes. With the advances of field-programmable gate arrays, application specific integrated circuits, and high-speed data converters, in recent years, digital signal processing (DSP) has been able to play an increasingly important role in RoF system/processing. Such an analog-digital coordinated scheme, namely, DSP-enhanced RoF, has merits in flexibility, parallelized processing capability, and robustness. This paper aims to provide comprehensive analysis of three major DSP-enhanced RoF techniques, namely, DSP-based intermediate-frequency over fiber, analog-to-digital compression RoF, and delta-sigma RoF. Besides performance, quantitative and qualitative analysis will be presented on latency, power consumption, and system complexity, attributes that are important in practice. In addition, we will discuss the challenges to and opportunities for future research.