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Sökning: WFRF:(Agrell Erik 1965 )

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41.
  • Agrell, Erik, 1965 (författare)
  • Nonlinear fiber capacity
  • 2013
  • Ingår i: 39th European Conference and Exhibition on Optical Communication, ECOC 2013; London; United Kingdom; 22 September 2013 through 26 September 2013. - : Institution of Engineering and Technology. - 9781849197595 ; :622 CP, s. 630-632
  • Konferensbidrag (refereegranskat)abstract
    • In this semi-tutorial presentation, we review fundamental information theory for links with and without memory, in the linear and nonlinear regimes. A comparison between channel models with long (but finite) memory and infinite memory yields an unexpected result.
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42.
  • Agrell, Erik, 1965, et al. (författare)
  • On optimal constellations for BICM at low SNR
  • 2009
  • Ingår i: Proceedings IEEE Information Theory Workshop ITW 2009, Taormina, Italy [Best Poster Award]. - 9781424449835 ; , s. 480-484
  • Konferensbidrag (refereegranskat)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_b/N_0=-1.59 dB. For equiprobable input distributions, a constellation achieves this limit if and only if it is a linear projection of a hypercube.
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43.
  • Agrell, Erik, 1965, et al. (författare)
  • On the Best Lattice Quantizers
  • 2023
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 69:12, s. 7650-7658
  • Tidskriftsartikel (refereegranskat)abstract
    • A lattice quantizer approximates an arbitrary real-valued source vector with a vector taken from a specific discrete lattice. The quantization error is the difference between the source vector and the lattice vector. In a classic 1996 paper, Zamir and Feder show that the globally optimal lattice quantizer (which minimizes the mean square error) has white quantization error: for a uniformly distributed source, the covariance of the error is the identity matrix, multiplied by a positive real factor. We generalize the theorem, showing that the same property holds (i) for any lattice whose mean square error cannot be decreased by a small perturbation of the generator matrix, and (ii) for an optimal product of lattices that are themselves locally optimal in the sense of (i). We derive an upper bound on the normalized second moment (NSM) of the optimal lattice in any dimension, by proving that any lower- or upper-triangular modification to the generator matrix of a product lattice reduces the NSM. Using these tools and employing the best currently known lattice quantizers to build product lattices, we construct improved lattice quantizers in dimensions 13 to 15, 17 to 23, and 25 to 48. In some dimensions, these are the first reported lattices with normalized second moments below the best known upper bound.
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44.
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45.
  • Agrell, Erik, 1965, et al. (författare)
  • On the symbol error probability of regular polytopes
  • 2011
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 57:6, s. 3411-3415
  • Tidskriftsartikel (refereegranskat)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. © 2011 IEEE.
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46.
  • Agrell, Erik, 1965 (författare)
  • On the Voronoi neighbor ratio for binary linear block codes
  • 1998
  • Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 44:7, s. 3064-3072
  • Tidskriftsartikel (refereegranskat)abstract
    • Soft-decision decoding of block codes is regarded as the geometrical problem of identifying the Voronoi region within which a given input vector lies. A measure, called the neighbor ratio, is proposed to characterize how many facets a Voronoi region has. Theory and algorithms are presented to determine the neighbor ratio for binary linear block codes and results are given for several types of codes. An asymptotic analysis for long codes reveals that the neighbor ratio depends on whether the code rate is less than 1/2 or not. For rates below this threshold, all pairs of codewords tend to share a Voronoi facet; for higher rates, a relatively small fraction of them do.
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47.
  • Agrell, Erik, 1965, et al. (författare)
  • Optimal Alphabets and Binary Labelings for BICM at Low SNR
  • 2011
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 57:10, s. 6650-6672
  • Tidskriftsartikel (refereegranskat)abstract
    • Optimal binary labelings, input distributions, and input alphabets are analyzed for the so-called bit-interleaved coded modulation (BICM) capacity, paying special attention to the low signal-to-noise ratio (SNR) regime. For 8-ary pulse amplitude modulation (PAM) and for 0.75 bit/symbol, the folded binary code results in a higher capacity than the binary reflected gray code (BRGC) and the natural binary code (NBC). The 1 dB gap between the additive white Gaussian noise (AWGN) capacity and the BICM capacity with the BRGC can be almost completely removed if the input symbol distribution is properly selected. First-order asymptotics of the BICM capacity for arbitrary input alphabets and distributions, dimensions, mean, variance, and binary labeling are developed. These asymptotics are used to define first-order optimal (FOO) constellations for BICM, i.e. constellations that make BICM achieve the Shannon limit $-1.59 \tr{dB}$. It is shown that the $\Eb/N_0$ required for reliable transmission at asymptotically low rates in BICM can be as high as infinity, that for uniform input distributions and 8-PAM there are only 72 classes of binary labelings with a different first-order asymptotic behavior, and that this number is reduced to only 26 for 8-ary phase shift keying (PSK). A general answer to the question of FOO constellations for BICM is also given: using the Hadamard transform, it is found that for uniform input distributions, a constellation for BICM is FOO if and only if it is a linear projection of a hypercube. A constellation based on PAM or quadrature amplitude modulation input alphabets is FOO if and only if they are labeled by the NBC; if the constellation is based on PSK input alphabets instead, it can never be FOO if the input alphabet has more than four points, regardless of the labeling.
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48.
  • Agrell, Erik, 1965, et al. (författare)
  • Optimization of lattices for quantization
  • 1998
  • Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 44:5, s. 1814-1828
  • Tidskriftsartikel (refereegranskat)abstract
    • A training algorithm for the design of lattices for vector quantization is presented. The algorithm uses a steepest descent method to adjust a generator matrix, in the search for a lattice whose Voronoi regions have minimal normalized second moment. The numerical elements of the found generator matrices are interpreted and translated into exact values. Experiments show that the algorithm is stable, in the sense that several independent runs reach equivalent lattices. The obtained lattices reach as low second moments as the best previously reported lattices, or even lower. Specifically, we report lattices in nine and ten dimensions with normalized second moments of 0.0716 and 0.0708, respectively, and nonlattice tessellations in seven and nine dimensions with 0.0727 and 0.0711, which improves on previously known values. The new nine- and ten-dimensional lattices suggest that Conway and Sloane's (1993) conjecture on the duality between the optimal lattices for packing and quantization might be false. A discussion of the application of lattices in vector quantizer design for various sources, uniform and nonuniform, is included.
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49.
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50.
  • Agrell, Erik, 1965, et al. (författare)
  • Performance Prediction Recipes for Optical Links
  • 2021
  • Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 33:18, s. 1034-1037
  • Tidskriftsartikel (refereegranskat)abstract
    • Although forward error-correction (FEC) coding is an essential part of modern fiber-optic communication systems, it is impractical to implement and evaluate FEC in transmission experiments and simulations. Therefore, it is desirable to accurately predict the end-to-end link performance including FEC from transmission data recorded without FEC. In this tutorial, we provide ready-to-implement “recipes” for such prediction techniques, which apply to arbitrary channels and require no knowledge of information or coding theory. The appropriate choice of recipe depends on properties of the FEC encoder and decoder. The covered metrics include bit error rate, symbol error rate, achievable information rate, and asymptotic information, in all cases computed using a mismatched receiver. Supplementary software implementations are available.
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Agrell, Erik, 1965 (332)
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