As the emergence of various high-bandwidth services
and the requirementsto support 5G/Wi-Fi 6 wireless networks, the
next generation fixed networks, i.e. F5G, are expected to be
realized in the 5G era. F5G is endowed with new characteristics,
including ultra-high bandwidth, all-optical connections and
optimal service experience. In terms of signal transmission,
intensity modulation direct-detection (IM-DD) is favorable due to
its simple architecture. The fundamental challenge associated with
direct-detection is the disappearance of the transmitted signal’s
phase. Along with the IMDD’s nonlinear effects, limited
bandwidth and power fading degrade the system transmission
performance. Advanced modulation and coherent detection are
also attractive to support large capacity access, however, the
complexity and low power consumption need to be solved
properly. In terms of access, the flexibility and low latency are the
two key factors affecting service experience. In this article, we
review the evolution of PONs and the challenges of current PONs
in detail. We analyze key enabling digital signal processing (DSP)
techniques, including detection linearization for direct-detection
and coherent detection, adaptive equalizers, digital filer enabled
flexible access and low-latency inter-OUN communications.
Finally, we discuss the developing trends of future fixed access
networks.