Two-level coding for efficient digital radio-over-fiber transmission with unequal bit protection

Abstract

The digital radio-over-fiber (D-RoF) transmission with two-level coding (TLC) is proposed and demonstrated in this Letter. A joint design considering the importance of quantization bits, the protection ability of forward error correction (FEC), and the bit error ratio of quadrature amplitude modulation (QAM) symbols is realized. In TLC-based D-RoF systems, the more significant bits among quantization bits are protected by a FEC and are assigned to the least reliable bits of modulated QAM symbols. Conversely, the less significant bits, without FEC protection, are allocated to the more reliable bits of QAM symbols. Experiments on an 11-km standard single-mode fiber transmission are conducted to evaluate the performance. The results indicate that, with a maximum iteration number of 2, compared to the conventional bit-interleaved coded modulation (BICM) with all bits encoded, the D-RoF based on TLC attains nearly identical performance under the 0.34% error vector magnitude threshold of 65536QAM wireless signals, specifically achieving complexity reductions of 54.55% and 67.66% for 16QAM and 64QAM optical transmissions, respectively.