SNR Improved Digital-Analog Radio-Over-Fiber Scheme for a Millimeter Wireless Fronthaul

We propose a multi-order digital-analog radio-over-fiber (DA-RoF) scheme with different quantization factors at each stage and verify it experimentally in a D-band photonics-aided RoF transmission system. The 10-Gbaud multi-order DA-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 78.13 Gb/s/λ is successfully transmitted in a 130-GHz 4.6-km wireless link. The calculated capacity-distance product is 359.4 Gb/s/λ·km with a spectral efficiency (SE) of 7.81 bit/s/Hz. Results show that the 4-order DA-RoF scheme achieves a maximum recovered signal-to-noise ratio (SNR) of 38.26 dB and minimum error vector magnitude (EVM) of 1.22%, which meets the requirement of 4096-quadrature-amplitude-modulation (4096-QAM) transmission. Compared with the traditional analog-RoF (A-RoF) scheme, an average SNR enhancement of 3.8 dB for each linearly increased bandwidth is achieved in the DA-RoF scheme. Our work suggests many optimistic possibilities for the low-cost 5G wireless fronthaul and future radio access networks.