取代光通信系统设计中的软 FEC 极限范式
Replacing the Soft FEC Limit Paradigm in the Design of Optical Communication Systems
AI总结：
本文指出软 FEC 极限范式不适用于软判决逐比特解码，证明广义互信息可跨信道与调制格式更准确预测 FEC 后 BER，并通过线性、非线性全场仿真和实验验证。
摘要：
FEC 极限范式是设计光通信系统以在不使用前向纠错（FEC）的情况下达到某一误码率（BER）时的普遍做法。该做法假设存在一种 FEC 码，能够在解码后将 BER 降低到期望水平。本文对这一做法提出质疑，并证明对于软判决逐比特解码而言，与信道无关的 FEC 极限概念并不成立。结果表明，在低码率和高阶调制格式下，使用软 FEC 极限范式对频谱效率的低估最高可达 20%。解码后 BER 的更好预测指标是广义互信息；研究表明，该指标能够在不同信道条件和调制格式下给出一致的 FEC 后 BER 预测。为验证理论分析，本文在线性和非线性传输两种情形下开展了大量光学全场仿真与实验。
英文摘要：
The FEC limit paradigm is the prevalent practice for designing optical communication systems to attain a certain bit-error rate (BER) without forward error correction (FEC). This practice assumes that there is an FEC code that will reduce the BER after decoding to the desired level. In this paper, we challenge this practice and show that the concept of a channel-independent FEC limit is invalid for soft-decision bit-wise decoding. It is shown that for low code rates and high order modulation formats, the use of the soft FEC limit paradigm can underestimate the spectral efficiencies by up to 20%. A better predictor for the BER after decoding is the generalized mutual information, which is shown to give consistent post-FEC BER predictions across different channel conditions and modulation formats. Extensive optical full-field simulations and experiments are carried out in both the linear and nonlinear transmission regimes to confirm the theoretical analysis.
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