Exploiting the Faster-Than-Nyquist Concept in Wavelength-Division Multiplexing Systems Using Duobinary Shaping

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[Abstract] This paper begins with Nyquist wavelength-division multiplexing (WDM) and then introduces faster-than-Nyquist. In faster-than-Nyquist, a certain amount of inter-symbol interference (ISI) is accepted, which violates the fundamental principle of Nyquist WDM. This results in much-relaxed transceiver bandwidth and simpler spectral design. However, in faster-than-Nyquist, implementation complexity is shifted from the transmitter side to the receiver side. Therefore, successful application of faster-than-Nyquist depends on innovation in the receiver structure. In this paper, we discuss the guidelines for implementing suboptimum, low-complexity receivers based on faster-than-Nyquist. We suggest that duobinary shaping is a good technique for trading off achievable spectral efficiency, detection performance, and implementation complexity and might be preferable to Nyquist WDM. Experiments are conducted to verify robustness of the proposed technique.

[Keywords] coherent detection; digital signal processing; optical fiber communications; spectral-efficiency; wavelength division multiplexing