| 21. |
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| 22. |
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| 23. |
- Alvarado, Alex, 1982, et al.
(författare)
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Four-Dimensional Coded Modulation with Bit-Wise Decoders for Future Optical Communications
- 2015
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 33:10, s. 1993-2003
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Tidskriftsartikel (refereegranskat)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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| 24. |
- Alvarado, Alex, 1982, et al.
(författare)
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LDPC codes for optical channels: Is the "FEC limit" a good predictor of post-FEC BER?
- 2015
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Ingår i: 2015 Optical Fiber Communications Conference and Exhibition, (OFC) 2015, Los Angeles, United States, 22-26 March 2015. - Washington, D.C. : OSA. - 9781557529374 ; , s. 7121706-
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Konferensbidrag (refereegranskat)abstract
- We answer the question in the title negatively. More precisely, the FEC limit is invalid for soft decision decoding and low to medium code rates. A better predictor is the generalized mutual information.
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| 25. |
- Alvarado, A., et al.
(författare)
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Replacing the Soft-Decision FEC Limit Paradigm in the Design of Optical Communication Systems
- 2016
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 34:2, s. 707-721
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Tidskriftsartikel (refereegranskat)abstract
- 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 bit-wise decoding. It is shown that for low code rates and high-order modulation formats, the use of the soft-decision 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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| 26. |
- Alvarado, A., et al.
(författare)
-
Replacing the Soft-Decision FEC Limit Paradigm in the Design of Optical Communication Systems
- 2015
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 33:20, s. 4338-4352
-
Tidskriftsartikel (refereegranskat)abstract
- 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 bit-wise decoding. It is shown that for low code rates and high-order modulation formats, the use of the soft-decision 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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| 27. |
- Bhar, Chayan, 1988, et al.
(författare)
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Channel allocation in elastic optical networks using traveling salesman problem algorithms
- 2019
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Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 11:10, s. C58-C66
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Tidskriftsartikel (refereegranskat)abstract
- Elastic optical networks have been proposed to support high data rates in metro and core networks. However, frequency allocation of the channels (i.e., channel ordering) in such networks is a challenging problem. This requires arranging the optical channels within the frequency grid with the objective of ensuring a minimum signal-to-noise ratio (SNR). An optimal arrangement results in the highest SNR margin for the entire network. However, determining the optimal arrangement requires an exhaustive search through all possible arrangements (permutations) of the channels. The search space increases exponentially with the number of channels. This discourages an algorithm employing an exhaustive search for the optimal frequency allocation. We utilize the Gaussian noise (GN) model to formulate the frequency allocation (channel ordering) problem as a variant of the traveling salesman problem (TSP) using graph theory. Thereafter, we utilize graph-theoretic tools for the TSP from the existing literature to solve the channel ordering problem. Performance figures obtained for the proposed scheme show that it is marginally inferior to the optimal search (through all possible permutations) and outperforms any random allocation scheme. Moreover, the proposed scheme is implementable for a scenario with a large number of channels. In comparison, an exhaustive search with the GN model and split-step Fourier method simulations are shown to be feasible for a small number of channels only. It is also illustrated that the SNR decreases with an increase in bandwidth when the frequency separation is high.
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| 28. |
- Correia, Fabio, et al.
(författare)
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Parallel Improved Schnorr-Euchner Enumeration SE++ for the CVP and SVP
- 2016
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Ingår i: 24th Euromicro International Conference on Parallel, Distributed, and Network-Based Processing, PDP 2016, Heraklion, Crete, Greece, 17-19 February 2016. - 9781467387750 ; , s. 596-603
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Konferensbidrag (refereegranskat)abstract
- The Closest Vector Problem (CVP) and the Shortest Vector Problem (SVP) are prime problems in lattice-based cryptanalysis, since they underpin the security of many lattice-based cryptosystems. Despite the importance of these problems, there are only a few CVP-solvers publicly available, and their scalability was never studied. This paper presents a scalable implementation of an enumeration-based CVP-solver for multi-cores, which can be easily adapted to solve the SVP. In particular, it achieves super-linear speedups in some instances on up to 8 cores and almost linear speedups on 16 cores when solving the CVP on a 50-dimensional lattice. Our results show that enumeration-based CVP-solvers can be parallelized as effectively as enumeration-based solvers for the SVP, based on a comparison with a state of the art SVP-solver. In addition, we show that we can optimize the SVP variant of our solver in such a way that it becomes 35%-60% faster than the fastest enumeration-based SVP-solver to date.
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| 29. |
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| 30. |
- Czegledi, Cristian Bogdan, 1988, et al.
(författare)
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Digital backpropagation accounting for polarization-mode dispersion
- 2017
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 25:3, s. 1903-1915
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Tidskriftsartikel (refereegranskat)abstract
- Digital backpropagation (DBP) is a promising digital-domain technique to mitigate Kerr-induced nonlinear interference. While it successfully removes deterministic signal-signal interactions, the performance of ideal DBP is limited by stochastic effects, such as polarizationmode dispersion (PMD). In this paper, we consider an ideal full-field DBP implementation and modify it to additionally account for PMD; reversing the PMD effects in the backward propagation by passing the reverse propagated signal also through PMD sections, which concatenated equal the inverse of the PMD in the forward propagation. These PMD sections are calculated analytically at the receiver based on the total accumulated PMD of the link estimated from channel equalizers. Numerical simulations show that, accounting for nonlinear polarization-related interactions in the modified DBP algorithm, additional signal-to-noise ratio gains of 1.1 dB are obtained for transmission over 1000 km.
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