Zhang Junwei, Tan Heyun, Hong Xiaojian, Liu Jie, Guo Changjian, Fei Chao, Wu Xiong, Tao Lau Alan Pak, Yu Siyuan, Lu Chao
Opt Express. 2022 Sep 26;30(20):36343-36357. doi: 10.1364/OE.468635.
To cope with the nonlinear distortions and the chromatic dispersion (CD) induced power fading in double-side band (DSB) intensity modulation and direct detection (IM/DD) transmission systems, high-performance Volterra nonlinear equalizers (VNLEs) including Volterra feed-forward equalizer (VFFE) and Volterra decision-feedback equalizer (VDFE) are widely applied. However, the conventional VNLEs have high computational complexity, especially for longer memory lengths. In this paper, based on sparse and weight-sharing strategies for significant kernel reduction, we propose four low-complexity NLEs including a sparse diagonally pruned VDFE (S-DP-VDFE), a sparse diagonally pruned absolute-term DFE (S-DP-ATDFE), a weight-sharing DP-VDFE (WS-DP-VDFE), and a weight-sharing DP-ATDFE (WS-DP-ATDFE), and present a comprehensive comparison among them in terms of computational complexity and bit error ratio (BER) performance in a C-band 100-Gbit/s PAM-4 transmission system over 60-km standard single-mode fiber (SSMF). The experimental results show that the proposed S-DP-VDFE and WS-DP-VDFE not only exhibit comparable performance with the conventional DP-VDFE but also reduce the complexity by 54.5% and 45.9%, respectively. While the proposed S-DP-ATDFE and WS-DP-ATDFE yield lower complexity at the expense of a slight performance degradation. Compared with the proposed S-DP-VDFE, S-DP-ATDFE, and WS-DP-VDFE, the proposed WS-DP-ATDFE with the lowest number of real-valued multiplications of 45 achieves up to 90.9%, 81.6%, and 95.8% complexity reduction, respectively, at the 7% hard-decision forward error correction (HD-FEC) BER limit of 3.8 × 10. The proposed low-complexity WS-DP-ATDFE shows great potential in low-cost and high-performance IM/DD optical transmission systems.
为了应对双边带（DSB）强度调制和直接检测（IM/DD）传输系统中的非线性失真以及色散（CD）引起的功率衰落，包括Volterra前馈均衡器（VFFE）和Volterra判决反馈均衡器（VDFE）在内的高性能Volterra非线性均衡器（VNLE）被广泛应用。然而，传统的VNLE具有很高的计算复杂度，尤其是对于较长的记忆长度。在本文中，基于用于显著减少内核的稀疏和权重共享策略，我们提出了四种低复杂度的非线性均衡器，包括稀疏对角修剪VDFE（S-DP-VDFE）、稀疏对角修剪绝对项DFE（S-DP-ATDFE）、权重共享DP-VDFE（WS-DP-VDFE）和权重共享DP-ATDFE（WS-DP-ATDFE），并在60公里标准单模光纤（SSMF）上的C波段100 Gbit/s PAM-4传输系统中，对它们在计算复杂度和误码率（BER）性能方面进行了全面比较。实验结果表明，所提出的S-DP-VDFE和WS-DP-VDFE不仅与传统的DP-VDFE表现出相当的性能，而且分别将复杂度降低了54.5%和45.9%。而所提出的S-DP-ATDFE和WS-DP-ATDFE以轻微的性能下降为代价实现了更低的复杂度。与所提出的S-DP-VDFE、S-DP-ATDFE和WS-DP-VDFE相比，所提出的WS-DP-ATDFE具有最低的45个实值乘法数量，在3.8×10的7%硬判决前向纠错（HD-FEC）误码率限制下，分别实现了高达90.9%、81.6%和95.8%的复杂度降低。所提出的低复杂度WS-DP-ATDFE在低成本和高性能IM/DD光传输系统中显示出巨大潜力。
