The soft-output successive cancellation list (SO-SCL) decoder provides a methodology for estimating the a-posteriori probability log-likelihood ratios by only leveraging the conventional SCL decoder of polar codes. However, the sequential decoding nature of SCL introduces high decoding latency to SO-SCL. In this paper, we incorporate node-based fast decoding into the SO-SCL framework. After addressing the challenge of soft output extraction in special node decoding, we proposed the soft-output fast SCL (SO-FSCL) decoding algorithm, along with its log-domain implementation and hardware-friendly version. The proposed SO-FSCL decoder can be regarded as an add-on extension to FSCL decoder, enabling us to autonomously choose whether to output only hard decisions like FSCL or to provide additional soft outputs. Latency and complexity analyses demonstrate that SO-FSCL can significantly reduce, for example, decoding time steps by 81.8\% (with unlimited resources), the number of additions by 41.3\%, and the number of comparisons by 46.4\%. Meanwhile, simulation results indicate that SO-FSCL delivers almost the same soft-output performance as SO-SCL, outperforming other soft-output polar decoders, especially in scenarios involving iterative decoding.

翻译：软输出逐次相消列表（SO-SCL）译码器提供了一种仅利用传统极化码SCL译码器来估计后验概率对数似然比的方法。然而，SCL的逐次译码特性导致SO-SCL具有较高译码延迟。本文将基于节点的快速译码融入SO-SCL框架中。在解决特殊节点译码中软输出提取难题后，我们提出了软输出快速SCL（SO-FSCL）译码算法，并给出了其对数域实现及硬件友好型版本。所提出的SO-FSCL译码器可视为FSCL译码器的附加扩展，使我们能够自主选择是仅输出硬判决（如FSCL）还是额外提供软输出。延迟与复杂度分析表明，SO-FSCL能显著减少译码时间步长（在无限资源条件下减少81.8%）、加法操作数量（减少41.3%）以及比较操作数量（减少46.4%）。同时，仿真结果表明，SO-FSCL在软输出性能上与SO-SCL几乎相同，优于其他软输出极化码译码器，尤其是在涉及迭代译码的场景中。