Performance Enhanced Cascaded Digital-Analog Radio-Over-Fiber Enabled by Digital Symbol Remapping for 6G Mobile Fronthaul

In this paper, we introduce a novel performance enhanced cascaded digital–analog radio-over-fiber (ECDA-RoF) scheme achieved by a digital symbol remapping technique for 6G mobile Fronthaul. After the digital symbol remapping, the entropy of the digital part generated by the traditional CDA-RoF scheme will be reduced, indicating an improvement in the channel noise tolerance for this part. Consequently, a larger rounding factor can be supported to enhance the signal-to-noise ratio (SNR) of the recovered wireless signal. The effectiveness of the proposed scheme is verified through simulation using 32 Gbaud multi-order CDA-RoF signals. The results indicate that, at the channel SNR of 20 dB, for 32 Gbuad 2-order and 3-order ECDA-RoF signals, about 4.3 dB and 5 dB recovered wireless SNR enhancement can be achieved compared to 32 Gbuad 2-order and 3-order CDA-RoF signals, respectively. Maintaining the same recovered wireless SNR, the channel SNR will be reduced by approximately 1 dB for both 32 Gbuad 2-order and 3-order ECDA-RoF signals. Proof-of-concept experiments have been established for the 32 Gbuad 2-order and 3-order ECDA-RoF and CDA-RoF signals in the coherent system to further illustrate the effectiveness of the proposed scheme. The experiment results indicate that, after 10-km single-mode fiber (SMF) transmission, about 6.2 dB and 7.8 SNR enhancement can be achieved for the recovered wireless signal as the 2-order and 3-order CDA-RoF schemes are transitioned to the 2-order and 3-order ECDA-RoF schemes, respectively.