相干光传输系统中几何形状的多维调制解调器
Geometrically-Shaped Multi-Dimensional Modulation Formats in Coherent Optical Transmission Systems
摘要：
在多维（MD）空间中对调制格式进行整形是在加性高斯白噪声（AWGN）信道和光纤信道中获得频谱效率增益的有效方法。本文第一部分对现有的用于光纤通信的MD几何形状调制进行了综述。研究表明，通过利用维度中的相关性或/和增加调制格式的基数，可以获得较大的增益。实际的限制和挑战也讨论了有效的解决方案。在第二部分中，我们通过最大化AWGN信道的广义互信息，将最近提出的基于正交对称约束的四维（4D）调制格式族扩展到高达10 bit/4D-sym的高频谱效率。多跨光纤传输系统的可达性增加了25%。最后，在最近引入的非线性干涉（NLI）模型的帮助下，为单跨光纤系统设计非线性容忍的4D调制格式的优化。仿真结果表明，所提出的基于NLI模型的4D调制格式可以提高有效信噪比约0.25 dB的AWGN信道优化的4D调制格式。
英文摘要：
Shaping modulation formats in multi-dimensional (MD) space is an effective approach to harvest spectral efficiency gains in both the additive white Gaussian noise (AWGN) channel and the optical fiber channel. In the first part of this paper, existing MD geometrically-shaped modulations for fiber optical communications are reviewed. It is shown that large gains can be obtained by exploiting correlation in the dimensions or/and by increasing the cardinality of the modulation format. Practical limitations and challenges are also discussed together with efficient solutions. In the second part, we extend the recently proposed four-dimensional (4D) modulation format family based on the constraint of orthant-symmetry to high spectrum efficiencies up to 10 bit/4D-sym by maximizing generalized mutual information for AWGN channel. Reach increases of up to 25% for a multi-span optical fiber transmission system are reported. Lastly,with the help of a recently introduced nonlinear interference (NLI) model, an optimization for designing nonlinear-tolerant 4D modulation formats is introduced for a single-span optical fiber system. Simulation results show that the proposed NLI model-based 4D modulation format could increase the effective SNRs by 0.25 dB with respect to the AWGN channel-optimal 4D modulation format.
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