Channel measurements for a 50G passive optical network (PON) show a significant amount of intersymbol interference (ISI) due to chromatic dispersion (CD) and the use of low-cost, bandwidth-limited 25 Gbaud class components. The channel characteristics at the input of the forward error correction (FEC) decoder are measured for several receiver equalization schemes, and the error correlation at the output of each equalizer is characterized using a sub-class of a Fritchman’s Markov model. This model is used to generate error sequences that match the observed correlation statistics, and these sequences are then used to evaluate the performance of a candidate low-density parity-check (LDPC) code with lifting factor 256 and hard-input decoding. It is shown that for a bandwidth-limited 50G PON system with 83 ps/nm dispersion, the optical power sensitivity penalty (OPSP) due to a reduction in error correction performance caused by correlated errors is 0.3–0.6 dB. Precoding, i.e., differential encoding of the input data and differential decoding, helps to reduce the OPSP for some equalizers, but the penalty increases for other equalizers. The use of a 256-bit segment-interleaver only marginally improves the decoding performance, whereas bit-interleaving across four codewords reduces the penalty to within 0.05 dB relative to the binary symmetric channel.

中文翻译：

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使用马尔可夫模型对50G PON中的均衡引起的相关误差进行硬输入FEC评估

50G无源光网络（PON）的信道测量结果表明，由于色散（CD）和使用低成本，带宽受限的25 Gbaud类组件，导致出现大量符号间干扰（ISI）。针对几种接收机均衡方案，测量前向纠错（FEC）解码器输入端的信道特性，并使用Fritchman马尔可夫模型的子类来表征每个均衡器输出端的误差相关性。该模型用于生成与观察到的相关性统计信息匹配的错误序列，然后将这些序列用于评估具有提升因子256和硬输入解码的候选低密度奇偶校验（LDPC）码的性能。结果表明，对于带宽为83 ps / nm的带宽受限的50G PON系统，由于相关误差引起的纠错性能下降，导致光功率灵敏度损失（OPSP）为0.3–0.6 dB。预编码，即输入数据的差分编码和差分解码，有助于减少某些均衡器的OPSP，但其他均衡器的代价会增加。256位分段交织器的使用仅略微提高了解码性能，而相对于二进制对称信道，跨四个码字的位交织将代价降低到0.05 dB以内。