Experimental Performance of 4D Optimized Constellation Alternatives for PM-8QAM and PM-16QAM

Buelow, Henning; Lu, Xiaofeng; Schmalen, Laurent; Klekamp, A.; Buchali, Fred

doi:10.1364/ofc.2014.m2a.6

Cited by 14 publications

(12 citation statements)

References 9 publications

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“…This is usually known as BICM with iterative demapping (BICM-ID). BICM-ID for optical communications has been studied in [21]- [23], [24,Sec. 3], [25,Sec.…”

Section: Introductionmentioning

confidence: 99%

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Four-Dimensional Coded Modulation with Bit-Wise Decoders for Future Optical Communications

Alvarado

Agrell

2015

J. Lightwave Technol.

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Abstract-Coded modulation (CM) is the combination of forward error correction (FEC) and multilevel constellations. Coherent optical communication systems result in a four-dimensional (4D) signal space, which naturally leads to 4D-CM transceivers. A practically attractive design paradigm is to use a bit-wise decoder, where the detection process is (suboptimally) separated into two steps: soft-decision demapping followed by binary decoding. In this paper, bit-wise decoders are studied from an information-theoretic viewpoint. 4D constellations with up to 4096 constellation points are considered. Metrics to predict the post-FEC bit-error rate (BER) of bit-wise decoders are analyzed. The mutual information is shown to fail at predicting the post-FEC BER of bit-wise decoders and the so-called generalized mutual information is shown to be a much more robust metric. For the suboptimal scheme under consideration, it is also shown that constellations that transmit and receive information in each polarization and quadrature independently (e.g., PM-QPSK, PM-16QAM, and PM-64QAM) outperform the best 4D constellations designed for uncoded transmission. Theoretical gains are as high as 4 dB, which are then validated via numerical simulations of low-density parity check codes.

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“…This is usually known as BICM with iterative demapping (BICM-ID). BICM-ID for optical communications has been studied in [21]- [23], [24,Sec. 3], [25,Sec.…”

Section: Introductionmentioning

confidence: 99%

“…4D constellations optimized in this sense were compared in [31]. Spherically shaped 4D constellations based on the D 4 lattice were studied in, e.g., [23], [33]. Somewhat less power efficient, but easier to implement, are the cubically shaped constellations based on D 4 , called set-partitioning QAM [33], [34].…”

Section: Introductionmentioning

confidence: 99%

Four-Dimensional Coded Modulation with Bit-Wise Decoders for Future Optical Communications

Alvarado

Agrell

2015

J. Lightwave Technol.

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“…This structure is known as BICM-ID and was introduced in [11]- [13]. BICM-ID for optical communications has been studied in [14]- [16], [7,Sec. 3], [17,Sec.…”

mentioning

confidence: 99%

Replacing the Soft-Decision FEC Limit Paradigm in the Design of Optical Communication Systems

Alvarado

Agrell

Lavery

et al. 2015

J. Lightwave Technol.

271

183

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The FEC limit paradigm is the prevalent practice for designing optical communication systems to attain a certain bit-error rate (BER) without forward error correction (FEC). This practice assumes that there is an FEC code that will reduce the BER after decoding to the desired level. In this paper, we challenge this practice and show that the concept of a channel-independent FEC limit is invalid for soft-decision bitwise decoding. It is shown that for low code rates and high order modulation formats, the use of the soft FEC limit paradigm can underestimate the spectral efficiencies by up to 20%. A better predictor for the BER after decoding is the generalized mutual information, which is shown to give consistent post-FEC BER predictions across different channel conditions and modulation formats. Extensive optical full-field simulations and experiments are carried out in both the linear and nonlinear transmission regimes to confirm the theoretical analysis.

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“…More recently proposed 4D-2A8PSK is another example of the 4D constant modulus modulation. It has been widely recognized that DP-Star-8QAM for 6 bits/symbol does not perform very well, and many formats have been investigated [21][22][23][24][25] for this spectral efficiency. In particular, 4D-2A8PSK with the spectral efficiency of 6 bits/symbol has been shown to have superior linear and nonlinear performance than many other formats, because of its large Euclidean distance, 4D constant modulus characteristics (i.e., constant power in each time slot), and Gray labeling [26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Nonlinearity-Tolerant Modulation Formats for Coherent Optical Communications

Kojima¹,

Koike‐Akino²,

Yoshida³

et al. 2018

Selected Topics on Optical Fiber Technologies and Applications

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Fiber nonlinearity is the main factor limiting the transmission distance of coherent optical communications. We overview several modulation formats intrinsically tolerant to fiber nonlinearity. We recently proposed family of 4D modulation formats based on 2-ary amplitude 8-ary phase-shift keying (2A8PSK), covering the spectral efficiency of 5, 6, and 7 bits/4D symbol, which will be explained in detail in this chapter. These coded modulation formats fill the gap of spectral efficiency between DP-QPSK and DP-16QAM, showing superb performance both in linear and nonlinear regimes. Since these modulation formats share the same constellation and use different parity bit expressions only, digital signal processing can accommodate those multiple modulation formats with minimum additional complexity. Nonlinear transmission simulations indicate that these modulation formats outperform the conventional formats at each spectral efficiency. We also review DSP algorithms and experimental results. Their application to time-domain hybrid modulation for 4-8 bits/4D symbol is also reviewed. Furthermore, an overview of an eight-dimensional 2A8PSK-based modulation format based on a Grassmann code is also given. All these results indicate that the 4D-2A8PSK family show great promise of excellent linear and nonlinear performances in the spectral efficiency between 3.5 and 8 bits/4D symbol.

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Experimental Performance of 4D Optimized Constellation Alternatives for PM-8QAM and PM-16QAM

Abstract: Sensitivity and reach of soft-decoded PM-8QAM was improved by 1.2-dB and 35%, respectively, by moving to a 64 point 4D constellation and iterative decoding. Replacing PM-16QAM by 256 4D points led to 0.3-dB gain only.

Cited by 14 publications

References 9 publications

Four-Dimensional Coded Modulation with Bit-Wise Decoders for Future Optical Communications

Four-Dimensional Coded Modulation with Bit-Wise Decoders for Future Optical Communications

Replacing the Soft-Decision FEC Limit Paradigm in the Design of Optical Communication Systems

Nonlinearity-Tolerant Modulation Formats for Coherent Optical Communications

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