90 research outputs found
Experimental Demonstration of Geometrically-Shaped Constellations Tailored to the Nonlinear Fibre Channel
A geometrically-shaped 256-QAM constellation, tailored to the nonlinear
optical fibre channel, is experimentally demonstrated. The proposed
constellation outperforms both uniform and AWGN-tailored 256-QAM, as it is
designed to optimise the trade-off between shaping gain, nonlinearity and
transceiver impairments
74.38 Tb/s Transmission Over 6300 km Single Mode Fibre Enabled by C plus L Amplification and Geometrically Shaped PDM-64QAM
Ultrawide-bandwidth optical amplification over almost 90 nm, covering the C+L bands, is described. Complemented by system-tailored geometrical constellation shaping and nonlinearity compensation, it enabled a record capacity transmission of 74.38 Tb/s over 6,300 km of G.654 single-mode fibre. The hybrid scheme, combining backward Raman pre-amplification with EDFA, significantly improves the average effective noise figure across the entire bandwidth, allowing the use of span lengths of 70 km. The system-tailored GS-64QAM constellation was optimised to both linear link impairments and transceiver nonlinearities, improving the gap to the AWGN channel capacity relative to square 64QAM from 0.6 bit/symbol to 0.35 bit/symbol. We experimentally evaluated the system performance using the bit-wise achievable information rate (AIR) and signal-to-noise ratio (SNR) at the end of transmission, as well as post SD-FEC BER
High-Cardinality Geometrical Constellation Shaping for the Nonlinear Fibre Channel
This paper presents design methods for highly efficient optimisation of
geometrically shaped constellations to maximise data throughput in optical
communications. It describes methods to analytically calculate the
information-theoretical loss and the gradient of this loss as a function of the
input constellation shape. The gradients of the \ac{MI} and \ac{GMI} are
critical to the optimisation of geometrically-shaped constellations. It
presents the analytical derivative of the achievable information rate metrics
with respect to the input constellation. The proposed method allows for
improved design of higher cardinality and higher-dimensional constellations for
optimising both linear and nonlinear fibre transmission throughput.
Near-capacity achieving constellations with up to 8192 points for both 2 and 4
dimensions, with generalised mutual information (GMI) within 0.06 bit/2Dsymbol
of additive white Gaussian noise channel (AWGN) capacity, are presented.
Additionally, a design algorithm reducing the design computation time from days
to minutes is introduced, allowing the presentation of optimised constellations
for both linear AWGN and nonlinear fibre channels for a wide range of
signal-to-noise ratios
Signal Design and Machine Learning Assisted Nonlinearity Compensation for Coherent Optical Fibre Communication Links
This thesis investigates low-complexity digital signal processing (DSP) for signal design and nonlinearity compensation strategies to improve the performance of single-mode optical fibre links over different distance scales.
The performance of a novel ML-assisted inverse regular perturbation technique that mitigates fibre nonlinearities was investigated numerically with a dual-polarization 64 quadrature amplitude modulation (QAM) link over 800 km distance. The model outperformed the heuristically-optimised digital backpropagation approach with <5 steps per span and mitigated the gain expansion issue, which limits the accuracy of an untrained model when the balance between the nonlinear and linear components becomes considerable.
For short reach links, the phase noise due to low-cost, high-linewidth lasers is a more significant channel impairment. A novel constellation optimisation algorithm was, therefore, proposed to design modulation formats that are robust against both additive white Gaussian noise (AWGN) and the residual laser phase noise (i.e., after carrier phase estimation). Subsequently, these constellations were numerically validated in the context of a 400ZR standard system, and achieved up to 1.2 dB gains in comparison with the modulation formats which were optimised only for the AWGN channel.
The thesis concludes by examining a joint strategy to modulate and demodulate signals in a partially-coherent AWGN (PCAWGN) channel. With a low-complexity PCAWGN demapper, 8- to 64-ary modulation formats were designed and validated through numerical simulations. The bit-wise achievable information rates (AIR) and post forward error correction (FEC) bit error rates (BER) of the designed constellations were numerically validated with: the theoretically optimum, Euclidean (conventional), and low-complexity PCAWGN demappers. The resulting constellations demonstrated post-FEC BER shaping gains of up to 2.59 dB and 2.19 dB versus uniform
64 QAM and 64-ary constellations shaped for the purely AWGN channel model, respectively.
The described geometric shaping strategies can be used to either relax linewidth and/or carrier phase estimator requirements, or to increase signal-to-noise ratio (SNR) tolerance of a system in the presence of residual phase noise
Polarization-ring-switching for nonlinearity-tolerant geometrically-shaped four-dimensional formats maximizing generalized mutual information
In this paper, a new four-dimensional 64-ary polarization ring switching
(4D-64PRS) modulation format with a spectral efficiency of 6 bit/4D-sym is
introduced. The format is designed by maximizing the generalized mutual
information (GMI) and by imposing a constant-modulus on the 4D structure. The
proposed format yields an improved performance with respect to state-of-the-art
geometrically shaped modulation formats for bit-interleaved coded modulation
systems at the same spectral efficiency. Unlike previously published results,
the coordinates of the constellation points and the binary labeling of the
constellation are jointly optimized. When compared with
polarization-multiplexed 8-ary quadrature-amplitude modulation (PM-8QAM), gains
of up to 0.7 dB in signal-to-noise ratio are observed in the additive white
Gaussian noise (AWGN) channel. For a long-haul nonlinear optical fiber system
of 8,000 km, gains of up to 0.27 bit/4D-sym (5.5% data capacity increase) are
observed. These gains translate into a reach increase of approximately 16%
(1,100 km). The proposed modulation format is also shown to be more tolerant to
nonlinearities than PM-8QAM. Results with LDPC codes are also presented, which
confirm the gains predicted by the GMI.Comment: 12 pages, 12 figure
On the Performance Limits of High-speed Transmission using a Single Wideband Coherent Receiver
The performance of a wideband coherent receiver was investigated. The relative impact of digital pre-distortion, geometric constellation shaping and pilot sequence detection, as well as the number of sub-channels in the super-channel, on the receiver performance was explored. The detection of a net data rate of 2.36 Tb/s after 75 km transmission of a 8 × 26 GBd DP-GS-256-QAM super-channel was demonstrated using a single 110 GHz electrical bandwidth receiver. The overall improvement due to the digital pre-distortion and tailored geometric constellation shaping was 1.2 bit/4D-sym in the achievable information rate.
Advanced Digital Signal Processing Techniques for High-Speed Optical Links
L'abstract è presente nell'allegato / the abstract is in the attachmen
Multidimensional Optimized Optical Modulation Formats
This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation
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