面向短距离光互连的低延迟低复杂度MLSE (Low-Latency and Low-Complexity MLSE for Short-Reach Optical Interconnects)

To meet the high-speed, low-latency, and low-complexity demand for optical interconnects, simplified layered 2-step maximum likelihood sequence estimation (L2S-MLSE) is proposed in this paper. Simplified L2S-MLSE combines computational simplification and reduced state in L2S-MLSE. L2S-MLSE with a parallel sliding block architecture reduces latency from linear order to logarithmic order. Computational simplification reduces the number of multipliers from exponential order to linear order. Incorporating the reduced state with computational simplification further decreases the number of adders and comparators. The simplified L2S-MLSE is evaluated in a 112-Gbit/s PAM4 transmission over 2-km standard single-mode fiber. Experimental results show that the simplified L2S-MLSE significantly outperforms the FFE-only case in bit error ratio (BER) performance. Compared with simplified 1-step MLSE, the latency of simplified L2S-MLSE is reduced from 34 delay units in linear order to 7 delay units in logarithmic order. The simplified scheme in L2S-MLSE reduces the number of variable multipliers from 512 in exponential order to 33 in linear order without BER performance deterioration, while reducing the number of adders and comparators to 37.2% and 8.4%, respectively, with nearly identical BER performance.

翻译：为满足光互连对高速率、低延迟与低复杂度的需求，本文提出简化的分层两步最大似然序列估计（L2S-MLSE）。简化的L2S-MLSE融合了L2S-MLSE中的计算简化与状态缩减。采用并行滑动块架构的L2S-MLSE将延迟从线性量级降低至对数量级。计算简化将乘法器数量从指数量级减少至线性量级。在计算简化的基础上结合状态缩减，可进一步减少加法器与比较器的数量。简化的L2S-MLSE在2公里标准单模光纤的112 Gbit/s PAM4传输系统中进行了性能评估。实验结果表明，在误码率（BER）性能方面，简化的L2S-MLSE显著优于仅使用FFE的方案。与简化的一步MLSE相比，简化L2S-MLSE的延迟从线性量级的34个延迟单元降低至对数量级的7个延迟单元。L2S-MLSE中的简化方案将可变乘法器数量从指数量级的512个减少至线性量级的33个，且未造成BER性能下降；同时将加法器与比较器数量分别减少至原方案的37.2%与8.4%，且保持几乎相同的BER性能。