SNR improved digital-cascaded-pulse-code-modulation radio-over-fiber scheme supporting 16,777,216 QAM for mobile fronthaul

We propose a digital-cascaded-pulse-code-modulation radio-over-fiber (DCP-RoF) scheme and verify it experimentally in a coherent transmission system. The 50-Gbaud 2-order 6-bit DCP-RoF signal with a common public radio interface equivalent data rate of ${279}\;{\rm Gb/s/}\lambda$ is successfully transmitted in a 10-km standard single-mode fiber link. Results show that the 2-order 6-bit DCP-RoF scheme achieves a maximum recovered signal-to-noise ratio (SNR) of 83.43 dB, which meets the requirements for 16,777,216-quadrature-amplitude-modulation (16,777,216-QAM) transmission. The DCP-RoF scheme has advantages over analog RoF and digital-analog RoF in terms of SNR improvement, as well as advantages over digital RoF (D-RoF) in spectral efficiency. Furthermore, an average SNR enhancement of 13.48 dB for each linearly increased bandwidth is achieved in the DCP-RoF scheme. Our work suggests many optimistic possibilities for the future radio access networks and mobile fronthaul.