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Proceedings Paper

Comparison of advanced DSP techniques for spectrally efficient Nyquist-WDM signal generation using digital FIR filters at transmitters based on higher-order modulation formats
Author(s): Yi Weng; Junyi Wang; Zhongqi Pan
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Paper Abstract

To support the ever-increasing demand for high-speed optical communications, Nyquist spectral shaping serves as a promising technique to improve spectral efficiency (SE) by generating near-rectangular spectra with negligible crosstalk and inter-symbol interference in wavelength-division-multiplexed (WDM) systems. Compared with specially-designed optical methods, DSP-based electrical filters are more flexible as they can generate different filter shapes and modulation formats. However, such transmitter-side pre-filtering approach is sensitive to the limited taps of finite-impulse-response (FIR) filter, for the complexity of the required DSP and digital-to-analog converter (DAC) is limited by the cost and power consumption of optical transponder. In this paper, we investigate the performance and complexity of transmitter-side FIR-based DSP with polarization-division-multiplexing (PDM) high-order quadrature-amplitude-modulation (QAM) formats. Our results show that Nyquist 64-QAM, 16-QAM and QPSK WDM signals can be sufficiently generated by digital FIR filters with 57, 37, and 17 taps respectively. Then we explore the effects of the required spectral pre-emphasis, bandwidth and resolution on the performance of Nyquist-WDM systems. To obtain negligible OSNR penalty with a roll-off factor of 0.1, two-channel-interleaved DAC requires a Gaussian electrical filter with the bandwidth of 0.4–0.6 times of the symbol rate for PDM-64QAM, 0.35–0.65 times for PDM-16QAM, and 0.3–0.8 times for PDM-QPSK, with required DAC resolutions as 8, 7, 6 bits correspondingly. As a tradeoff, PDM-64QAM can be a promising candidate for SE improvement in next-generation optical metro networks.

Paper Details

Date Published: 13 February 2016
PDF: 13 pages
Proc. SPIE 9773, Optical Metro Networks and Short-Haul Systems VIII, 977305 (13 February 2016); doi: 10.1117/12.2206098
Show Author Affiliations
Yi Weng, Univ. of Louisiana at Lafayette (United States)
Junyi Wang, Qualcomm Technologies, Inc. (United States)
Zhongqi Pan, Univ. of Louisiana at Lafayette (United States)


Published in SPIE Proceedings Vol. 9773:
Optical Metro Networks and Short-Haul Systems VIII
Atul K. Srivastava; Werner Weiershausen; Benjamin B. Dingel; Achyut K. Dutta, Editor(s)

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