Abstract Sampling frequency offset between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) always exists in asynchronous optical discrete multi-tone (DMT) systems. The overall bit error rate (BER) performance may be seriously deteriorated due to SFO-induced phase rotation. Inter-symbol differential encoding/detection (ISDE/ISDD) with decision-aided residual phase compensation (RPC) has been employed to compensate SFO. No extra training sequences or pilot subcarriers are required for SFO compensation. However, the increased phase noise induced by ISDD is still a problem and may degrade the BER performance of the DMT receiver, especially for high-order modulation formats. In this work, we propose the use of amplitude and phase shift keying (APSK) constellation scheme to against the ISDD-induced phase noise and then improve the BER performance. In our simulations, the 64QAM and two types of 64APSK modulation formats for DMT are studied in both additive white Gaussian noise (AWGN) channel and intensity-modulation/direct-detection optical fiber transmission system. The simulated results exhibit that the employed two 64APSK constellation schemes outperform the conventional 64QAM modulation format in the presence of ISDD-induced phase noise. By using the proposed 64APSK constellation scheme, the SNR performance can be improved by up to 3dB when the BER is 1E-3 in AWGN channel. Besides, up to 2dB improvement in the receiver sensitivity in terms of the received optical power can be also achieved, compared to the conventional 64QAM modulation format.

中文翻译：

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具有 ISDD 启用 SFO 补偿的用于短距离 DMT 的 64APSK 星座方案

摘要 在异步光离散多音（DMT）系统中，数模转换器（DAC）和模数转换器（ADC）之间的采样频偏始终存在。由于 SFO 引起的相位旋转，整体误码率 (BER) 性能可能会严重恶化。具有决策辅助残余相位补偿 (RPC) 的符号间差分编码/检测 (ISDE/ISDD) 已被用于补偿 SFO。SFO 补偿不需要额外的训练序列或导频子载波。然而，由 ISDD 引起的增加的相位噪声仍然是一个问题，可能会降低 DMT 接收器的 BER 性能，尤其是对于高阶调制格式。在这项工作中，我们建议使用幅度和相移键控 (APSK) 星座方案来对抗 ISDD 引起的相位噪声，从而提高 BER 性能。在我们的模拟中，在加性高斯白噪声 (AWGN) 信道和强度调制/直接检测光纤传输系统中研究了用于 DMT 的 64QAM 和两种类型的 64APSK 调制格式。仿真结果表明，在存在 ISDD 引起的相位噪声的情况下，采用的两种 64APSK 星座方案优于传统的 64QAM 调制格式。通过使用所提出的 64APSK 星座方案，当 AWGN 信道中的 BER 为 1E-3 时，SNR 性能可以提高高达 3dB。此外，在接收光功率方面，接收器灵敏度还可以实现高达 2dB 的提高，