SNR Improved Digital-PCM Radio-Over-Fiber Scheme Supporting 65536 QAM for Mobile Fronthaul

We propose a digital pulse-code-modulation radio-over-fiber (DP-RoF) scheme and verify it experimentally in a 10-km standard single-mode fiber (SSMF) coherent system. The 20-Gbaud DP-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 112 Gb/s is successfully transmitted in the system with excellent performance. The recovered signal-to-noise ratio (SNR) of wireless signal in DP-RoF scheme is 50.14 dB, which is 26.62, 20.01 and 13.28 dB higher than that of analog radio-over-fiber (A-RoF), digital-analog radio-over-fiber (DA-RoF) and digital radio-over-fiber (D-RoF), respectively. The DP-RoF scheme meets the error vector magnitude (EVM) requirement of 65536 quadrature amplitude modulation (QAM), while A-RoF and DA-RoF schemes cannot reach the EVM threshold of 1024 QAM. With improved SNR, the proposed DP-RoF system is a promising scheme for ultra-high-order QAM transmission in future 6G fronthaul.