High-Fidelity Digital Coherent Fronthaul Employing Bit Interleaving and Geometric Shaping

Coherent detection has gradually gained acceptance for digital radio-over-fiber (D-RoF). In D-RoF transmission, quantized wireless waveform bits require unequal bit protection (UBP) due to their varying importance, unlike conventional digital communication where all bits in 0/1 streams hold equal significance. In this letter, we propose and experimentally demonstrate an interleaved uneven modulation-based UBP (IUM-UBP) scheme for high-fidelity coherent digital fronthaul. Bit interleaving and geometric shaping are employed to ensure the superior performance of more important bits. In the experiment, the proposed scheme achieves significant improvements in recovered signal-to-noise ratio (SNR) of wireless waveform, reaching 35.5 dB, 20.5 dB, and 10.2 dB gain when using quantization bits of 16, 12, and 8, respectively. The results demonstrate that the proposed IUM-UBP scheme provides a viable solution for flexible and high-fidelity coherent digital fronthaul.