The explosive growth of mobile applications, e.g., ultra-high definition video streaming, virtual reality/augmented reality (VR/AR) wearables, incurs lots of changes in 5G network of its reliability, coverage, transmission throughput and received quality of service (QoS). Therefore, to make 5G a reality, Fiber-Wireless Integration and Networking (FiWIN) is the key architecture in serving such diverse user scenarios, which provides a comprehensive network design for signal delivery. In this paper, some of the great challenges in 5G mobile fronthaul and the possible solutions will be discussed. In particular, we will review the recent breakthroughs in the FiWIN research center of the digitally spreading OFDM, polarization division multiplexing (PDM) radio-over-fiber (RoF), and beamforming enhanced mobile fronthaul. From the network perspective, by employing the 5G new radio and dense small cells deployment, the 5G wireless environment could become sophisticated, and the unexpected interference would cause a significant received performance declination. In this case, a spreading OFDM exhibit a superior received performance over the typical OFDM is considering as a promising signal format. While, the photonic-aided RoF system greatly simplified the 5G small cell hardware design. In order to maintain that beneficial feature, a self-polarization PDM scheme may be applied in mobile fronthaul for increasing the channel capacity and network coverage. The narrow beam-width property of 5G new radio reduces the tolerance of antenna misalignment. To address such issue, we will present the future-proof experiment of the fiber-wireless integration network with a 1-by-4 beamforming receiver with full reception angles (±90o) and signal waveforms transparency.
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