592 Gbps/$\uplambda$ Capacity of Equivalent Fronthaul Channel Based on Time-Interleaved Digital-Analog Radio-Over-Fiber

We propose a novel time-interleaved hybrid digital-analog radio-over-fiber (TI-DA-ROF) scheme and verify it through experiments in a coherent optical communication system. This scheme relies on the digital symbols to measure the channel dynamics, based on which compatible DSP algorithms are conceived to compensate for the impairments that affect all DA symbols, thus enabling a robust RoF scheme against degradations, including polarization rotation, frequency offset, and phase noise. We conduct a numerical analysis to evaluate the performance of the DA-RoF scheme in different digital resolutions and to show its ability to tolerate MHz laser linewidth. In the proof-of-concept experiment, we demonstrate a high SNR gain of 12 dB at halved spectral efficiency. We test 256-QAM to 16384-QAM signals and calculate the effective SNR and EVM, demonstrating the transmission of 256-QAM and 1024-QAM signals achieving record capacity of the equivalent fronthaul channel (CEFC) of 674.66 Gbps and 592.01 Gbps, respectively. The experimental results show that the time-interleaved coherent DA-RoF system is a promising solution for the future beyond-5G/6G (B5G/6G) fronthaul.