Performance of momentum-based frequency-domain MIMO equalizer in the presence of feedback delay.
Performance of momentum-based frequency-domain MIMO equalizer in the presence of feedback delay.
复制标题
DOI：
10.1364/oe.394304
复制
发表时间：
2020-06
期刊：
影响因子：
3.8
通讯作者：
Wenting Yi;E. Sillekens;D. Lavery;Hubert Dzieciol;Sujie Zhou;K. Law;Jun Chen-;P. Bayvel;R. Killey
中科院分区：
文献类型：
--
作者：
Wenting Yi;E. Sillekens;D. Lavery;Hubert Dzieciol;Sujie Zhou;K. Law;Jun Chen-;P. Bayvel;R. Killey
针对偏振复用相干接收机，提出了一种采用基于动量的梯度下降更新算法的频域多输入多输出（FD-MIMO）均衡器。研究了其在动态变化的光通道下运行的性能，并评估了反馈环路中快速傅立叶变换 (FFT) 和其他数字信号处理 (DSP) 操作的延迟所引起的滤波器更新延迟的影响。我们表明，所提出的用于控制均衡器响应的基于动量的梯度下降算法比传统的梯度下降算法对反馈延迟具有更大的容忍度。我们考虑了 92 Gbaud 双极化 64 QAM 接收器，DSP 以每个符号两个样本运行，均衡器以 512 和 1024 个样本块运行（即 512/1024 点 FFT）。我们发现，在光信噪功率比 (OSNR) 为 35 dB 时，基于动量的梯度下降算法可以成功跟踪频率高达 50 kHz 的偏振态 (SOP) 旋转，滤波器更新延迟高达 14 个块 (39 ns)。相比之下，在其他方面相同的接收器中使用传统的梯度下降算法，均衡器性能在 SOP 旋转频率高于 20 kHz 时开始恶化。
A frequency-domain multiple-input multiple-output (FD-MIMO) equalizer employing a momentum-based gradient descent update algorithm is proposed for polarization multiplexing coherent receivers. Its performance in operation with dynamically varying optical channels is investigated and the impact of filter update delays, arising from the latency of the fast Fourier transforms (FFTs) and other digital signal processing (DSP) operations in the feedback loop, is assessed. We show that the proposed momentum-based gradient descent algorithm used to control the equalizer response has significantly greater tolerance to feedback delay than the conventional gradient descent algorithm. We considered a 92 Gbaud dual-polarization 64 QAM receiver, with DSP operating at two samples per symbol, and with the equalizer operating on blocks of 512 and 1024 samples (i.e., 512/1024-point FFT). We found that at an optical signal-to-noise power ratio (OSNR) of 35 dB, the momentum-based gradient descent algorithm can successfully track state-of-polarization (SOP) rotation at frequencies of up to 50 kHz and with filter update delays of up to 14 blocks (39 ns). In comparison, using the conventional gradient descent algorithm in an otherwise identical receiver, the equalizer performance starts to deteriorate at SOP rotation frequencies above 20 kHz.