Enhanced Digital Radio-Over-Fiber Transmission Using Unequal Bit Protection Based on Coding and Modulation

In digital radio-over-fiber (D-RoF) transmission for mobile fronthaul (MFH), wireless waveforms are digitized into quantization bits, which vary in importance for signal recovery. More important bits (MIBs) require enhanced protection compared to less important bits (LIBs). This paper proposes an unequal-bit-protection-based coding and modulation (UBP-CM) scheme that integrates forward error correction (FEC) and modulation in a joint design. Geometric constellation shaping (GCS) is employed to further enhance the protection of MIBs. Theoretical analysis of the UBP-CM with GCS aligns well with simulation results under an additive white Gaussian noise (AWGN) channel. In the experiments, a signal-to-noise ratio (SNR) gain of 23.1 dB is achieved over conventional bit-interleaved coded modulation (BICM), enabling the D-RoF system to support 16384-QAM wireless signals. Additionally, the maximum allowed symbol rate increases from 38 Gbaud to 58 Gbaud for the 1024-QAM threshold, representing a 52.6% improvement in the maximum line rate for D-RoF transmission.