SNR Improved Truncated-Digital-DSM Radio-Over-Fiber Scheme for Future Mobile Fronthaul

We propose a truncated digital delta-sigma modulated radio-over-fiber (TDDSM-RoF) scheme and verify it experimentally in a 10-km standard single-mode fiber (SSMF) coherent system. The 40-Gbaud TDDSM-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 0.214 Tb/s is successfully transmitted in the system with excellent performance. The recovered error vector magnitude (EVM) of TDDSM-RoF signal is 1.27%, meeting the EVM requirement for 4096-quadrature amplitude modulation (4096-QAM) transmission in fronthaul. Compared with the analog RoF (A-RoF) and digital-analog RoF (DA-RoF) schemes, the TDDSM-RoF scheme with a 6-times oversampling rate (6-OSR) DSM achieves signal-to-noise ratio (SNR) gains of 15.7 and 10.2 dB, respectively, at the cost of extra bandwidth. We also demonstrate a truncated-DA-RoF (TDA-RoF) scheme with analog quantization error. Although the TDA-RoF consumes less bandwidth than TDDSM-RoF, it has limited improvement in SNR. Compared with the commercial digital RoF (D-RoF) solution, the proposed TDA-RoF has an advantage in the required bandwidth and the TDDSM-RoF achieves a higher SNR gain and higher-QAM transmission. Both of them can serve as promising solutions for future 6G fronthaul.