| 51. |
- Agrell, Erik, 1965, et al.
(författare)
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Power-efficient modulation formats in coherent transmission systems
- 2009
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 27:22, s. 5115-5126
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Tidskriftsartikel (refereegranskat)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. © 2009, IEEE. All rights reserved.
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| 52. |
- Agrell, Erik, 1965, et al.
(författare)
-
Roadmap of optical communications
- 2016
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Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 18:6
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Tidskriftsartikel (refereegranskat)abstract
- Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.
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| 53. |
- Agrell, Erik, 1965, et al.
(författare)
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Satellite constellations: Towards the nonlinear channel capacity
- 2012
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Ingår i: 25th IEEE Photonics Conference, IPC 2012, Burlingame, 23 - 27 September 2012 [Invited]. - 9781457707315 ; , s. 316-317
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Konferensbidrag (refereegranskat)abstract
- We present a family of adaptive constellations that, in a nonlinear optical fiber channel model, has a mutual information (modulation-constrained capacity) that does not decrease with signal power.
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| 54. |
- Agrell, Erik, 1965, et al.
(författare)
-
Signal Shaping for BICM at Low SNR
- 2013
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 59:4, s. 2396-2410
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Tidskriftsartikel (refereegranskat)abstract
- The generalized mutual information (GMI) of bit-interleaved coded modulation (BICM) systems, sometimes called the BICM capacity, is investigated at low signal-to-noise ratio (SNR). The combinations of input alphabet, input distribution, and binary labeling that achieve the Shannon limit are completely characterized. The main conclusion is that a BICM system with probabilistic shaping achieves the Shannon limit at low SNR if and only if it can be represented as a zero-mean linear projection of a hypercube. Hence, probabilistic shaping offers no extra degrees of freedom to optimize the low-SNR BICM-GMI, in addition to what is provided by geometrical shaping. The analytical conclusions are confirmed by numerical results, which also show that for a fixed input alphabet, probabilistic shaping can improve the BICM-GMI in the low and medium SNR range.
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| 55. |
- Agrell, Erik, 1965
(författare)
-
Spectral coding by fast vector quantization
- 1993
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Ingår i: Proc. IEEE Workshop on Speech Coding for Telecommunications, Sainte-Adèle, Québec, Canada. ; , s. 61-62
-
Konferensbidrag (refereegranskat)
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| 56. |
- Agrell, Erik, 1965, et al.
(författare)
-
Upper bounds for constant-weight codes
- 2000
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 46:7, s. 2373-2395
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Tidskriftsartikel (refereegranskat)abstract
- Let A(n,d,w) denote the maximum possible number of codewords in an (n,d,w) constant-weight binary code. We improve upon the best known upper bounds on A(n,d,w) in numerous instances for n⩽24 and d⩽12, which is the parameter range of existing tables. Most improvements occur for d=8, 10, where we reduce the upper bounds in more than half of the unresolved cases. We also extend the existing tables up to n⩽28 and d⩽14. To obtain these results, we develop new techniques and introduce new classes of codes. We derive a number of general bounds on A(n,d,w) by means of mapping constant-weight codes into Euclidean space. This approach produces, among other results, a bound on A(n,d,w) that is tighter than the Johnson bound. A similar improvement over the best known bounds for doubly-constant-weight codes, studied by Johnson and Levenshtein, is obtained in the same way. Furthermore, we introduce the concept of doubly-bounded-weight codes, which may be thought of as a generalization of the doubly-constant-weight codes. Subsequently, a class of Euclidean-space codes, called zonal codes, is introduced, and a bound on the size of such codes is established. This is used to derive bounds for doubly-bounded-weight codes, which are in turn used to derive bounds on A(n,d,w). We also develop a universal method to establish constraints that augment the Delsarte inequalities for constant-weight codes, used in the linear programming bound. In addition, we present a detailed survey of known upper bounds for constant-weight codes, and sharpen these bounds in several cases. All these bounds, along with all known dependencies among them, are then combined in a coherent framework that is amenable to analysis by computer. This improves the bounds on A(n,d,w) even further for a large number of instances of n, d, and w.
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| 57. |
- Agrell, Erik, 1965
(författare)
-
Voronoi-Based Coding
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The performance of a digital communication system can generally be improved by increasing the number of variables being jointly coded. In this sense, it is desirable to have, e.g., higher-dimensional quantizers, longer channel codes, and more users in a multiple-access system. However, increasing the number of variables results in higher complexity of encoding and decoding, which are two limiting factors in the choice of coding methods. In this dissertation, which comprises seven published or submitted articles, algorithms are discussed for three related applications in telecommunications: vector quantizer encoding, multiuser detection, and soft-decision channel decoding. A unified approach is obtained through a common formulation in terms of discrete optimization, or, taking on a geometric viewpoint, searching in multidimensional point sets. A convenient instrument to characterize the structure of these sets is the Voronoi diagram. The first considered application is vector quantization, with some focus on lattices. Lattices are regular structures of infinitely many points that after truncation can be employed as quantizers. An algorithm is developed to optimize the quantization performance of lattices. Employing the algorithm, two lattices are found that improve on previous results. It is also discovered that the so-called D+ tessellation, which is a union of two lattices, is superior to any known single lattice in dimensions 7 and 9. Truncated lattices are also analyzed, revealing that their distortion in relation to that of optimal quantization increases with the number of points. An algorithm for quantizer design is introduced that maintains close to minimal distortion by suitably stretching the truncated lattice. The work on vector quantization also includes theory and algorithms for index assignment, which is a way to incorporate error-robustness into the quantizer design through a careful codevector ordering. Another contribution is a comparison of the complexity of some encoding methods. Multiuser detection in CDMA systems is formulated as the geometric problem of searching a point set having a certain structure. Properties of Voronoi diagrams of such structures are given, thus making it possible to apply a known Voronoi-based search algorithm for detection. Soft-decision decoding of block channel codes is the third application being studied, again by means of the Voronoi diagram. A fast algorithm is presented to investigate the Voronoi diagram of binary linear block codes. Several well-known codes are characterized. Asymptotic theory shows that for most classes of long codes, the complexity of the Voronoi diagram as a function of the bit rate displays a distinct threshold at the rate of one half. Voronoi-based soft decision decoding is essentially practicable only for rates above this value.
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| 58. |
- Agrell, Erik, 1965
(författare)
-
Voronoi regions for binary linear block codes
- 1996
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Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 42:1, s. 310-316
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Tidskriftsartikel (refereegranskat)abstract
- The Voronoi regions of a block code govern many aspects of the code's performance on a Gaussian channel, and they are fundamental instruments in, for example, error probability analysis and soft-decision decoding. The article presents an efficient method for finding the boundaries of the Voronoi regions for an arbitrary binary linear block code. Two theoretical results together lead to the Voronoi regions. First, it is shown that the question of the Voronoi neighborship can be reduced into testing a simpler relation, called the Gabriel neighborship. Second, a fast method of recognising Gabriel neighbors is proposed. These results are finally employed to describe the Voronoi regions for the Golay codes and several BCH codes, including Hamming codes.
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| 59. |
- Agrell, Erik, 1965, et al.
(författare)
-
WDM channel capacity and its dependence on multichannel adaptation models
- 2013
-
Ingår i: 2013 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC [Invited]. - 9781479904570
-
Konferensbidrag (refereegranskat)abstract
- Optical multichannel systems are often characterized by the channel capacity of a single channel, assuming a certain adaptation behavior of the other channels. We investigate some common adaptation models, which lead to dramatically different capacities.
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| 60. |
- Ahmad, Tauseef, 1986, et al.
(författare)
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Methodology for Power-Aware Coherent Receiver Design
- 2013
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701. ; , s. SPT4D.4-
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Konferensbidrag (refereegranskat)abstract
- We describe a methodology to design and evaluate DSP hardware for a coherent receiver. Important parameters that can be assessed include DSP power consumption and chip area.
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