对潜光纤通信中判决反馈滤波器的突发错误传播抑制
Burst-Error Propagation Suppression for Decision-Feedback Equalizer in Field-Trial Submarine Fiber-Optic Communications
摘要：
本文介绍了一个在南海18.8km无色散补偿海底光缆上进行的C波段72 Gbit/s光开关键控（OOK）系统的现场试验。18.8km海底光缆的色散（CD）导致72 Gbit/s OOK信号在36 GHz带宽上出现4个频谱零点，这是影响其误码率（BER）性能的主要障碍。判决反馈均衡器（DFE）是一种有效的频谱零点补偿方法。但是，当潜艇环境不稳定，出现突发错误时，DFE存在严重的突发错误传播缺陷。加权DFE（WDFE）可以用来减轻突发错误的传播，但它不能完全补偿频谱零点，因为只有一部分反馈符号是直接决定的。幸运的是，最大似然序列估计（MLSE）可以添加后的WDFE，同时消除抵抗频谱失真，实现最佳检测。与DFE和MLSE联合算法相比，WDFE和MLSE联合算法能有效地抑制突发错误传播，最大可使$\boldsymbol{Q}$因子提高2.9dB，并消除了BER floor现象。最大似然估计算法和WDFE算法的联合应用可以有效地解决光纤通信系统中突发错误的传播问题。
英文摘要：
In this paper, we present a field-trial C-band 72Gbit/s optical on-off keying (OOK) system over 18.8km dispersion-uncompensated submarine optical cable in the South China Sea. Chromatic dispersion (CD) of 18.8km submarine optical cable causes four spectral nulls on the 36GHz bandwidth of 72Gbit/s OOK signal, which is the main obstacle for achieving an acceptable bit-error-rate (BER) performance. Decision feedback equalizer (DFE) is effective to compensate for the spectral nulls. However, DFE has a serious defect of burst-error propagation when the burst errors emerge due to the unstable submarine environment. Weighted DFE (WDFE) can be used to mitigate the burst-error propagation, but it cannot fully compensate for the spectral nulls because only a part of feedback symbols is directly decided. Fortunately, maximum likelihood sequence estimation (MLSE) can be added after the WDFE to simultaneously eliminate the resisting spectral distortions and implement optimal detection. Compared to the joint DFE and MLSE algorithm, the joint WDFE and MLSE algorithm can effectively suppress the burst-error propagation to obtain a maximum 2.9dB improvement of $\boldsymbol{Q}$ factor and eliminate the phenomenon of BER floor. In conclusion, the joint WDFE and MLSE algorithm can solve the burst-error propagation for the field-trial fiber-optic communications.
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