A low-complexity soft-decision concatenated FEC scheme, consisting of an inner LDPC code and an outer staircase code, is proposed. The inner code is tasked with reducing the bit error probability ...below the outer-code threshold. The concatenated code is obtained by optimizing the degree distribution of the inner-code ensemble to minimize estimated data-flow, for various choices of outer staircase codes. A key feature that emerges from this optimization is that it pays to leave some inner codeword bits completely uncoded, thereby greatly reducing a significant portion of the decoding complexity. The tradeoff between required signal-to-noise ratio and decoding complexity of the designed codes is characterized by a Pareto frontier. Computer simulations of the resulting codes reveals that the net coding-gains of existing designs can be achieved with up to 71% reduction in complexity. A hardware-friendly quasi-cyclic construction is given for the inner codes, which can realize an energy-efficient decoder implementation, and even further complexity reductions via a layered message-passing decoder schedule.
Staircase Codes With 6% to 33% Overhead Zhang, Lei M.; Kschischang, Frank R.
Journal of lightwave technology,
05/2014, Letnik:
32, Številka:
10
Journal Article
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We design staircase codes with overheads between 6.25% and 33.3% for high-speed optical transport networks. Using a reduced-complexity simulation of staircase coded transmission over the BSC, we ...select code candidates from within a limited parameter space. Software simulations of coded BSC transmission are performed with algebraic component code decoders. The net coding gain of the best code designs are competitive with the best known hard-decision decodable codes over the entire range of overheads. At 20% overhead, staircase codes are within 0.92 dB of BSC capacity at a bit error-rate of <inline-formula><tex-math>10^{-15}</tex-math></inline-formula>. Decoding complexity and latency of the new staircase codes are also significantly reduced from existing hard-decision decodable schemes.
The nonlinear Fourier transform represents a signal in terms of its continuous spectrum, discrete eigenvalues, and the corresponding discrete spectral amplitudes. This paper presents a new ...bi-directional algorithm for computing the discrete spectral amplitudes, which addresses the significant problem of rounding errors inherent in previously known techniques. We use the proposed method to obtain accurate spectral-domain noise statistics for 2-soliton signals using numerical simulation.
We demonstrate, for a widely used model of channels with polarization-dependent loss (PDL), that channel capacity is achieved by a simple interference cancellation scheme in conjunction with a ...universal precoder. Crucially, the proposed scheme is not only information-theoretically optimal, but it is also exceptionally simple and concrete. It transforms the PDL channel into separate scalar additive white Gaussian noise channels, allowing off-the-shelf coding and modulation schemes designed for such channels to approach capacity. The signal-to-noise ratio (SNR) penalty incurred under 6 dB of PDL is reduced to the information-theoretic minimum of a mere 1 dB as opposed to the 4 dB SNR penalty incurred under naive over-provisioning.
Direct Detection Under Tukey Signalling Tasbihi, Amir; Kschischang, Frank R.
Journal of lightwave technology,
11/2021, Letnik:
39, Številka:
21
Journal Article
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A new direct-detection-compatible signalling scheme is proposed for fiber-optic communication over short distances. Controlled inter-symbol interference is exploited to extract phase information, ...thereby achieving spectral efficiencies about one bit less, per second per hertz, of those of a coherent detector.
The deliberate introduction of controlled intersymbol interference (ISI) in Tukey signalling enables the recovery of signal amplitude and (in part) signal phase under direct detection, giving rise to ...significant data rate improvements compared to intensity modulation with direct detection (IMDD). The use of an integrate-and-dump detector makes precise waveform shaping unnecessary, thereby equipping the scheme with a high degree of robustness to nonlinear signal distortions introduced by practical modulators. Signal sequences drawn from star quadrature amplitude modulation (SQAM) formats admit an efficient trellis description that facilitates codebook design and low-complexity near maximum-likelihood sequence detection in the presence of both shot noise and thermal noise. Under the practical (though suboptimal) allocation of a 50% duty cycle between ISI-free and ISI-present signalling segments, at a symbol rate of <inline-formula><tex-math notation="LaTeX">50\,</tex-math></inline-formula>Gbaud and a launch power of <inline-formula><tex-math notation="LaTeX">-10\,</tex-math></inline-formula>dBm the Tukey scheme has a maximum theoretically achievable throughput of <inline-formula><tex-math notation="LaTeX">200\,</tex-math></inline-formula>Gb/s with an (8,4)-SQAM constellation, while an IMDD scheme achieves about <inline-formula><tex-math notation="LaTeX">145\,</tex-math></inline-formula>Gb/s using PAM-8. Note that the two mentioned constellations have the same number of magnitude levels and the difference in throughput is resulting from exploiting phase information under using a complex-valued signal constellation.
A multistage signal estimation scheme is proposed for phase-and-amplitude modulated soliton communication systems. The estimator provides a significant mean-squared-error reduction in soliton ...amplitude estimation, which, in conjunction with detection of encoded phase information, results in spectral-efficiency improvements. A low-complexity version of the multistage estimation scheme is also proposed, whose performance is studied via numerical simulations under the distributed Raman amplification strategy. The achievable information rate is increased by about 1 bit/symbol for pulse bandwidth of 30 GHz, 40 GHz, and 50 GHz.
A pragmatic coded modulation system is presented that incorporates signal shaping and exploits the excellent performance and efficient high-speed decoding architecture of staircase codes. Reliable ...communication within 0.62 bits/s/Hz of the estimated capacity (per polarization) of a system with L =2000 km is provided by the proposed system, with an error floor below 10 -20 . Also, it is shown that digital backpropagation increases the achievable spectral efficiencies-relative to linear equalization-by 0.55 to 0.75 bits/s/Hz per polarization.
A low-complexity rate- and channel-configurable forward error-correction (FEC) scheme is proposed, consisting of an inner low-density parity-check code concatenated with an outer zipper code. A tool ...is developed to optimize a multi-level code architecture so that it can operate at multiple transmission rates, channel qualities, and modulation orders. The optimization criterion is selected to maintain a low estimated data-flow in its decoding operation. A hardware-friendly quasi-cyclic structure is considered for the inner code and the performance and complexity is reported for various designed FEC configurations. Compared to existing FEC schemes, the proposed designs deliver a similar performance with up to 63% reduction in decoding complexity or provide up to 0.6 dB coding gain at a similar decoding complexity.
This paper reviews digital signal processing techniques that compensate, mitigate, and exploit fiber nonlinearities in coherent optical fiber transmission systems.
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