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ABSTRACT: In this paper, the statistics of received signals in a single-channel dispersion-managed dual-polarization fiber-optical channel are derived in the limit of low dispersion. The joint probability density function (pdf) of the received amplitudes and phases of such a system is derived for both lumped and distributed amplification. The new pdf expressions are used to numerically evaluate the performance of modulation formats over channels with nonlinear phase noise. For example, a sensitivity gain of up to 2 dB is calculated for a specific system using polarization-multiplexed 8-ary phase-shift keying compared with a similar single-polarization system at the same spectral efficiency and a symbol error rate of 5 × 10<sup>-4</sup>. Moreover, the accuracy of the derived pdf is evaluated for some single-channel dispersion-managed fiber-optical links with different dispersion maps using the split-step Fourier transform method.
Journal of Lightwave Technology 09/2011; · 2.78 Impact Factor
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ABSTRACT: Recent results have shown that the performance of bit-interleaved coded modulation (BICM) using convolutional codes in nonfading channels can be greatly improved if the bit-level interleaver takes a trivial form (BICM-T), i.e., if it does not interleave the bits at all. The reported gains reach a few decibels and are obtained using a less complex BICM system. In this paper, we give a formal explanation for these results and show that BICM-T is in fact the combination of a TCM transmitter and a BICM receiver. Analytical bounds that predict the performance of BICM-T are developed and a new type of distance spectrum for the convolutional code is introduced.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: An exact expression is derived for the symbol error probability when the vertices of the four-dimensional 24-cell are used for digital transmission in Gaussian noise. Corresponding expressions for other regular convex polytopes are summarized. Numerically stable versions of these error probabilities are also obtained.
IEEE Transactions on Information Theory 07/2011; · 3.01 Impact Factor
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ABSTRACT: In this paper, the dimensionality of the multilevel coded modulation (MLCM) scheme is addressed. This study is done for an MLCM scheme with a N-dimensional (ND) constellation constructed from the Cartesian product of N identical 1D constellations in the high SNR regime. It is demonstrated that multidimensional MLCM with Reed-Solomon code components has better trade-off between coding gain and complexity than a 1D scheme. Specifically, a 4D MLCM system gains 1.4 dB over a 1D MLCM system with lower complexity at a block error of 10<sup>-6</sup>. The gain increases to 2.5 dB asymptotically.
IEEE Communications Letters 12/2010; · 0.98 Impact Factor
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ABSTRACT: Two algorithms for blind polarization demultiplexing, based on the constant modulus criterion and independent component analysis, are compared. It is found that the latter converges significantly faster to within a given SNR penalty tolerance.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
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ABSTRACT: A symbol-by-symbol phase noise estimation algorithm for polarization-multiplexed 16-QAM is evaluated. We found that it can cope with laser linewidths of up to 2.2 MHz in high SNR regimes, at 112 Gbit/s.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
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ABSTRACT: We investigate power-efficient modulation formats in the four-dimensional signal space that is used by most coherent transmission systems. The sensitivity and spectral efficiency trade-off is discussed, with and without forward error correction.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
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ABSTRACT: Coherent optical transmission systems have a four-dimensional (4-D) signal space (two quadratures in two polarizations). These four dimensions can be used to create modulation formats that have a better power efficiency (higher sensitivity) than the conventional binary phase shift keying/quadrature phase shift keying (BPSK/QPSK) signals. Several examples are given, with some emphasis on a 24-level format and an 8-level format, including descriptions of how they can be realized and expressions for their symbol and bit error probabilities. These formats are, respectively, an extension and a subset of the commonly used 16-level dual-polarization QPSK format. Sphere packing simulations in 2, 3, and 4 dimensions, up to 32 levels, are used to verify their optimality. The numerical results, as the number of levels increases, are shown to agree with lattice-theoretical results. Finally, we point out that the use of these constellations will lead to improved fundamental sensitivity limits for optical communication systems, and they may also be relevant as a way of reducing power demands and/or nonlinear influence.
Journal of Lightwave Technology 12/2009; · 2.78 Impact Factor
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ABSTRACT: In this paper we study the problem of finding capacity-maximizing constellations in BICM for asymptotically low signal-to-noise ratios (SNRs). We base our analysis on the so-called Hadamard transform and on a linear approximation of the BICM capacity for asymptotically low SNRs. We fully characterize the set of constellations, input distributions, and binary labelings that achieve Shannon's limit E<sub>b</sub>/N<sub>0</sub> = -1.59 dB. For equiprobable input distributions, a constellation achieves this limit if and only if it is a linear projection of a hypercube.
Information Theory Workshop, 2009. ITW 2009. IEEE; 11/2009
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ABSTRACT: In this paper the issue of improving the performance of iterative decoders based on sub-optimal calculation of the messages exchanged during iterations (L-values) is addressed. It is well known in the literature that a simple-yet very effective-way to improve the performance of suboptimal iterative decoders is based on applying a scaling factor to the L-values. In this paper, starting with a theoretical model based on the so-called consistency condition of a random variable, we propose a methodology for correcting the L-values that relies only on the distribution of the soft information exchanged in the iterative process. This methodology gives a clear explanation of why the well-known linear scaling factor provides a very good performance. Additionally, the proposed methodology allows us to avoid the exhaustive search required otherwise. Numerical simulations show that for turbo codes the scaling factors found closely follow the optimum values, which translates to a close-to-optimal BER performance. Moreover, for LDPC codes, the proposed methodology produces a better BER performance compared with the known method in the literature.
Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
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European Transactions on Telecommunications.
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Optical Fiber Communication Conference, OFC'2007;
