| 21. |
- Agrell, Erik, 1965
(författare)
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Capacity bounds in optical communications
- 2017
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Ingår i: European Conference on Optical Communication, ECOC. ; Volume 2017-September, s. 1-3
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Konferensbidrag (refereegranskat)abstract
- The fundamental concept of channel capacity and related information-theoretic metrics are reviewed and some techniques to quantify them by means of lower and upper bounds are explained. The importance of properly discretizing the channel model is highlighted.
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| 22. |
- Agrell, Erik, 1965, et al.
(författare)
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Capacity of a nonlinear optical channel with finite memory
- 2014
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 32:16, s. 2862-2876
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Tidskriftsartikel (refereegranskat)abstract
- The channel capacity of a nonlinear, dispersive fiber-optic link is revisited. To this end, the popular Gaussian noise (GN) model is extended with a parameter to account for the finite memory of realistic fiber channels. This finite-memory model is harder to analyze mathematically but, in contrast to previous models, it is valid also for nonstationary or heavy-tailed input signals. For uncoded transmission and standard modulation formats, the new model gives the same results as the regular GN model when the memory of the channel is about ten symbols or more. These results confirm previous results that the GN model is accurate for uncoded transmission. However, when coding is considered, the results obtained using the finite-memory model are very different from those obtained by previous models, even when the channel memory is large. In particular, the peaky behavior of the channel capacity, which has been reported for numerous nonlinear channel models, appears to be an artifact of applying models derived for independent input in a coded (i.e., dependent) scenario. © 1983-2012 IEEE.
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| 23. |
- Agrell, Erik, 1965, et al.
(författare)
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Closest point search in lattices
- 2002
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 48:8, s. 2201-2214
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Tidskriftsartikel (refereegranskat)abstract
- In this semitutorial paper, a comprehensive survey of closest point search methods for lattices without a regular structure is presented. The existing search strategies are described in a unified framework, and differences between them are elucidated. An efficient closest point search algorithm, based on the Schnorr-Euchner variation of the Pohst method, is implemented. Given an arbitrary point x is an element of R-m and a generator matrix for a lattice A, the algorithm computes the point of A that is closest to x. The algorithm is shown to be substantially faster than other known methods, by means of a theoretical comparison with the Kannan algorithm and an experimental comparison with the Pohst algorithm and its variants, such as the recent Viterbo-Boutros decoder. Modifications of the algorithm are developed to solve a number of related search problems for lattices, such as finding a shortest vector, determining the kissing number, computing the Voronoi-relevant vectors, and finding. a Korkine-Zolotareff reduced basis.
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| 24. |
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| 25. |
- Agrell, Erik, 1965
(författare)
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Conditions for a Monotonic Channel Capacity
- 2015
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 63:3, s. 738-748
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by results in optical communications, where the performance can degrade dramatically if the transmit power is sufficiently increased, the channel capacity is characterized for various kinds of memoryless vector channels. It is proved that for all static point-to-point channels, the channel capacity under an equal-power constraint is a nondecreasing function of power. As a consequence, maximizing the mutual information over all input distributions with a certain power is for such channels equivalent to maximizing it over the larger set of input distributions with upperbounded power. The channel coding theorem is formally proved for an equal-power constraint. For interference channels such as optical wavelength-division multiplexing systems, the primary channel capacity is always nondecreasing with power if all interferers transmit with identical distributions as the primary user. Also, if all input distributions in an interference channel are optimized jointly, then the achievable sum-rate capacity is again nondecreasing. The results generalize to the channel capacity as a function of a wide class of costs, not only power.
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| 26. |
- Agrell, Erik, 1965, et al.
(författare)
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Constant-weight code bounds from spherical code bounds
- 2000
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Ingår i: Proc. IEEE International Symposium on Information, Sorrento, Italy. - 0780358570 ; , s. 391-
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Konferensbidrag (refereegranskat)abstract
- We present new upper bounds on the size of constant-weight binary codes, derived from bounds for spherical codes. In particular, we improve upon the 1982 Johnson bound and the linear programming bound for constant-weight codes.
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| 27. |
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| 28. |
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| 29. |
- Agrell, Erik, 1965, et al.
(författare)
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First-order asymptotics of the BICM mutual information: Uniform vs. nonuniform distributions
- 2012
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Ingår i: Information Theory and Applications Workshop (ITA) 2012, San Diego, CA [Invited]. - 9781467314732 ; , s. 306 - 310
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Konferensbidrag (refereegranskat)abstract
- A linear, invertible transform is defined between two vectors or matrices as a tool for analyzing the bit-interleaved coded modulation (BICM) mutual information in the wideband regime. The transform coefficients depend on a set of real values, which can be interpreted as probabilities. The transform relates any BICM system with a nonuniform input distribution to another BICM system with a uniform distribution. Numerical evidence suggests that the two systems have the same first-order behavior, which would make possible to analyze nonuniform BICM systems based on known properties of uniform BICM systems.
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| 30. |
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