Yu Baoxian, Guo Changjian, Yi Langyu, Zhang Han, Liu Jie, Dai Xianhua, Lau Alan Pak Tao, Lu Chao
Opt Express. 2018 Nov 26;26(24):31075-31084. doi: 10.1364/OE.26.031075.
Spectral efficient frequency division multiplexing (SEFDM) can improve the spectral efficiency for next-generation optical and wireless communications. In this work, we apply SEFDM in beyond 100-Gb/s optical intensity modulation and direct detection transmissions and propose a low-complexity logarithmic-maximum-a-posteriori (log-MAP) Viterbi decoding algorithm to achieve the maximum likelihood (ML) detection. We evaluate the likelihood of detections using a posteriori probability instead of Euclidean distance by taking both noise and inter-carrier interference into consideration. In order to balance the performance and complexity, we then employ Viterbi decoding principle to retain only certain paths with ML detections (a.k.a., the surviving paths) while discarding the others during the decoding procedure. Results show that the proposed log-MAP Viterbi decoding scheme achieves optimal performance due to the precise likelihood evaluation, which guarantees the retention of the global ML detection. By using the proposed decoding scheme, the data rate of SEFDM signals can reach 150-Gb/s in a 2-km standard single mode fiber transmission, using only 28-GHz bandwidth and 16-QAM modulation. Experimental results show that the 16-QAM modulated SEFDM signal with a bandwidth compression factor of 0.8 outperforms 32-QAM modulated OFDM, while both signals have the same bandwidth (28-GHz) and data rate (140-Gb/s), which demonstrate the superiority of SEFDM in optical short reach applications.
频谱高效频分复用（SEFDM）可提高下一代光通信和无线通信的频谱效率。在这项工作中，我们将SEFDM应用于超过100 Gb/s的光强度调制和直接检测传输，并提出一种低复杂度对数最大后验概率（log-MAP）维特比译码算法以实现最大似然（ML）检测。我们通过考虑噪声和载波间干扰，使用后验概率而非欧几里得距离来评估检测的似然性。为了平衡性能和复杂度，我们随后采用维特比译码原理，在译码过程中仅保留具有ML检测结果的特定路径（即幸存路径），而舍弃其他路径。结果表明，由于精确的似然性评估，所提出的log-MAP维特比译码方案实现了最优性能，这保证了全局ML检测的保留。通过使用所提出的译码方案，在2公里标准单模光纤传输中，SEFDM信号的数据速率可达到150 Gb/s，仅使用28 GHz带宽和16-QAM调制。实验结果表明，带宽压缩因子为0.8的16-QAM调制SEFDM信号优于32-QAM调制的OFDM，而这两种信号具有相同的带宽（28 GHz）和数据速率（140 Gb/s），这证明了SEFDM在光短距离应用中的优越性。
