ZTE Communications

S pecial Topic
Exploiting the Faster-Than-Nyquist Concept in Wavelength-Division Multiplexing Systems Using Duobinary Shaping
Jianqiang Li, Ekawit Tipsuwannakul, Magnus Karlsson, and Peter A. Andrekson
Q Factor (dB)
11
10
9
8
7
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5
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-7
without Post-Filter+MLSD
-6 -5 -4 -3 -2 -1 0 1 2 3
Launched Power Per Channel PL (dBm)
MLSD: maximum-likelihood sequence detector
▲Figure 8. 640 km SSMF transmission performance versus launch
power per channel.
performance is mainly penalized by increased in-band noise
and interchannel linear crosstalk. In this case, more
nonlinearity is required to further penalize the signal.
6 Conclusion
Applying the faster-than-Nyquist concept in
spectrally-efficient WDM systems has been discussed. The
fundamental idea behind faster-than-Nyquist is to increase
spectral efficiency by accepting ISI. In light of this idea, we
have proposed a novel receiver structure based on duobinary
shaping in order to achieve a balanced trade-off between
spectral efficiency, detection performance, and
implementation complexity in optical WDM systems.
Experiments were carried out in 25 GHz-spaced 100 Gb/s
PM-QPSK WDM system with small implementation penalty
and promising robustness. The proposed scheme can be
expanded to higher-level modulation formats, for example,
16-ary quadrature amplitude modulation (QAM) for higher
spectral efficiency [25].
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