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Träfflista för sökning "WFRF:(Hug Florian) "

Sökning: WFRF:(Hug Florian)

  • Resultat 1-22 av 22
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1.
  • Bocharova, Irina, et al. (författare)
  • A Closed Form Expression for the Exact Bit Error Probability for Viterbi Decoding of Convolutional Codes
  • 2012
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 58:7, s. 4635-4644
  • Tidskriftsartikel (refereegranskat)abstract
    • In 1995, Best et al. published a formula for the exact bit error probability for Viterbi decoding of the rate R=1/2, memory m=1 (2-state) convolutional encoder with generator matrix G(D)=(1 1+D) when used to communicate over the binary symmetric channel. Their formula was later extended to the rate R=1/2, memory m=2 (4-state) convolutional encoder with generator matrix G(D)=(1+D^2 1+D+D^2) by Lentmaier et al. In this paper, a different approach to derive the exact bit error probability is described. A general recurrent matrix equation, connecting the average information weight at the current and previous states of a trellis section of the Viterbi decoder, is derived and solved. The general solution of this matrix equation yields a closed form expression for the exact bit error probability. As special cases, the expressions obtained by Best et al. for the 2-state encoder and by Lentmaier et al. for a 4-state encoder are obtained. The closed form expression derived in this paper is evaluated for various realizations of encoders, including rate R=1/2 and R=2/3 encoders, of as many as 16 states. Moreover, it is shown that it is straightforward to extend the approach to communication over the quantized additive white Gaussian noise channel.
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2.
  • Bocharova, Irina, et al. (författare)
  • A Greedy Search for Improved QC LDPC Codes with Good Girth Profile and Degree Distribution
  • 2012
  • Ingår i: IEEE International Symposium on Information Theory Proceedings (ISIT), 2012. - 9781467325806 ; , s. 3083-3087
  • Konferensbidrag (refereegranskat)abstract
    • Search algorithms for regular and irregular quasi-cyclic LDPC block codes with both good girth profile and good degree distribution are presented. New QC LDPC block codes of various code rates are obtained and their bit error rate performance is compared with that of the corresponding LDPC block codes defined in the IEEE 802.16 WiMAX standard of the same block length and code rate.
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3.
  • Bocharova, Irina, et al. (författare)
  • Another look at the exact bit error probability for Viterbi decoding of convolutional codes
  • 2011
  • Konferensbidrag (refereegranskat)abstract
    • In 1995, Best et al. published a formula for the exact bit error probability for Viterbi decoding of the rate R=1/2, memory m=1 (2-state) convolutional encoder with generator matrix G(D)=(1 1+D) when used to communicate over the binary symmetric channel. Their method was later extended to the rate R=1/2, memory m=2 (4-state) generator matrix G(D)=(1+D^2 1+D+D^2) by Lentmaier et al. In this paper, we shall use a different approach to derive the exact bit error probability. We derive and solve a general matrix recurrent equation connecting the average information weights at the current and previous steps of the Viterbi decoding. A closed form expression for the exact bit error probability is given. Our general solution yields the expressions for the exact bit error probability obtained by Best et al. (m=1) and Lentmaier et al. (m=2) as special cases. The exact bit error probability for the binary symmetric channel is determined for various 8 and 16 states encoders including both polynomial and rational generator matrices for rates R=1/2 and R=2/3. Finally, the exact bit error probability is calculated for communication over the quantized additive white Gaussian noise channel.
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4.
  • Bocharova, Irina, et al. (författare)
  • Double-Hamming based QC LDPC codes with large minimum distance
  • 2011
  • Ingår i: [Host publication title missing].
  • Konferensbidrag (refereegranskat)abstract
    • A new method using Hamming codes to construct base matrices of (J, K)-regular LDPC convolutional codes with large free distance is presented. By proper labeling the corresponding base matrices and tailbiting these parent convolutional codes to given lengths, a large set of quasi-cyclic (QC) (J, K)-regular LDPC block codes with large minimum distance is obtained. The corresponding Tanner graphs have girth up to 14. This new construction is compared with two previously known constructions of QC (J, K)-regular LDPC block codes with large minimum distance exceeding (J+1)!. Applying all three constructions, new QC (J, K)-regular block LDPC codes with J=3 or 4, shorter codeword lengths and/or better distance properties than those of previously known codes are presented.
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5.
  • Bocharova, Irina, et al. (författare)
  • Dual convolutional codes and the MacWilliams identities
  • 2012
  • Ingår i: Problems of Information Transmission. - 0032-9460. ; 48:1, s. 21-30
  • Tidskriftsartikel (refereegranskat)abstract
    • A recursion for sequences of spectra of truncated as well as tailbitten convolutional codes and their duals is derived. The order of this recursion is shown to be less than or equal to the rank of the weight adjacency matrix (WAM) for the minimal encoder of the convolutional code. It is sufficient to know finitely many spectra of these terminated convolutional codes in order to obtain an infinitely long sequence of spectra of their duals.
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6.
  • Bocharova, Irina, et al. (författare)
  • High-Rate QC LDPC Codes of Short and Moderate Length with Good Girth Profile
  • 2012
  • Ingår i: 7th International Symposium on Turbo Codes and Iterative Information Processing (ISTC), 2012. - 9781457721144 ; , s. 150-154
  • Konferensbidrag (refereegranskat)abstract
    • Irregular QC LDPC codes with parity-check matrices having different degree distributions are studied. A new algorithm for finding regular and irregular QC LDPC codes with a good girth profile as well as a good sliding-window girth is presented. As examples, simulation results for QC LDPC codes with good girth profile, rate R=4/5, and lengths about 1000, 2000, and 4000, constructed from base matrices with proper degree distributions are given. Their simulated BER and FER performances for belief propagation decoding are compared with the best previously known irregular QC LDPC codes of the same rate and length. It is shown that the constructed codes outperform the best previously known codes of same rate and lengths.
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7.
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8.
  • Bocharova, Irina, et al. (författare)
  • New low-density parity-check codes with large girth based on hypergraphs
  • 2010
  • Ingår i: [Host publication title missing].
  • Konferensbidrag (refereegranskat)abstract
    • The relation between low-density parity-check (LDPC) codes and hypergraphs supports searching for powerful LDPC codes based on hypergraphs. On the other hand, coding theory methods can be used in searching for hypergraphs with large girth. Moreover, compact representations of hypergraphs based on convolutional codes can be found. Algorithms for iteratively constructing LDPC codes with large girths and for determining their minimum distances are introduced. New quasi-cyclic (QC) LDPC codes are presented, some having both optimal girth and optimal minimum distance.
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9.
  • Bocharova, Irina, et al. (författare)
  • On the exact bit error probability for Viterbi decoding of convolutional codes
  • 2011
  • Konferensbidrag (refereegranskat)abstract
    • Forty years ago, Viterbi published upper bounds on both the first error event (burst error) and bit error probabilities for Viterbi decoding of convolutional codes. These bounds were derived using a signal flow chart technique for convolutional encoders. In 1995, Best et al. published a formula for the exact bit error probability for Viterbi decoding of the rate R=1/2, memory m=1 convolutional encoder with generator matrix G(D)=(1 1+D) when used to communicate over the binary symmetric channel. Their method was later extended to the rate R=1/2, memory m=2 generator matrix G(D)=(1+D^2 1+D+D^2) by Lentmaier et al. In this paper, we shall use a different approach to derive the exact bit error probability. We derive and solve a general matrix recurrent equation connecting the average information weights at the current and previous steps of the Viterbi decoding. A closed form expression for the exact bit error probability is given. Our general solution yields the expressions for the exact bit error probability obtained by Best et al. (m=1) and Lentmaier et al. (m=2) as special cases.
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10.
  • Bocharova, Irina, et al. (författare)
  • On weight enumerators and MacWilliams identity for convolutional codes
  • 2010
  • Ingår i: [Host publication title missing].
  • Konferensbidrag (refereegranskat)abstract
    • Convolutional codes are defined to be equivalent if their code symbols differ only in how they are ordered and two generator matrices are defined to be weakly equivalent (WE) if they encode equivalent convolutional codes. It is shown that tailbiting convolutional codes encoded by WE minimal-basic generator matrices have the same spectra. Shearer and McEliece showed that MacWilliams identity does not hold for convolutional codes. However, for the spectra of truncated convolutional codes and their duals, MacWilliams identity clearly holds. It is shown that the dual of a truncated convolutional code is not a truncation of a convolutional code but its reversal is. Finally, a recursion for the spectra of truncated convolutional codes is given and the spectral components are related to those for the corresponding dual codes.
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11.
  • Bocharova, Irina, et al. (författare)
  • Searching for voltage graph-based LDPC tailbiting codes with large girth
  • 2012
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 58:4, s. 2265-2279
  • Tidskriftsartikel (refereegranskat)abstract
    • The relation between parity-check matrices of quasi-cyclic (QC) low-density parity-check (LDPC) codes and biadjacency matrices of bipartite graphs supports searching for powerful LDPC block codes. Using the principle of tailbiting, compact representations of bipartite graphs based on convolutional codes can be found. Bounds on the girth and the minimum distance of LDPC block codes constructed in such a way are discussed. Algorithms for searching iteratively for LDPC block codes with large girth and for determining their minimum distance are presented. Constructions based on all-one matrices, Steiner Triple Systems, and QC block codes are introduced. Finally, new QC regular LDPC block codes with girth up to 24 are given.
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12.
  • Bocharova, Irina, et al. (författare)
  • Some Voltage Graph-Based LDPC Tailbiting Codes with Large Girth
  • 2011
  • Ingår i: [Host publication title missing].
  • Konferensbidrag (refereegranskat)abstract
    • The relation between the parity-check matrices of quasi-cyclic (QC) low-density parity-check (LDPC) codes and the biadjacency matrices of bipartite graphs supports searching for powerful LDPC block codes. Algorithms for searching iteratively for LDPC block codes with large girth are presented and constructions based on Steiner Triple Systems and short QC block codes are introduced, leading to new QC regular LDPC block codes with girth up to 24.
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13.
  • Bocharova, Irina, et al. (författare)
  • Woven convolutional graph codes with large free distances
  • 2011
  • Ingår i: Problems of Information Transmission. - 0032-9460. ; 47:1, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Constructions of woven graph codes based on constituent convolutional codes are studied and examples of woven convolutional graph codes are presented. The existence of codes, satisfying the Costello lower bound on the free distance, within the random ensemble of woven graph codes based on s-partite, s-uniform hypergraphs, where s depends only on the code rate, is shown. Simulation results for Viterbi decoding of woven graph codes are presented and discussed.
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14.
  • Hug, Florian, et al. (författare)
  • A rate R=5/20 hypergraph-based woven convolutional code with free distance 120
  • 2010
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 56:4, s. 1618-1623
  • Tidskriftsartikel (refereegranskat)abstract
    • A rate R=5/20 hypergraph-based woven convolu- tional code with overall constraint length 67 and constituent con- volutional codes is presented. It is based on a 3-partite, 3-uniform, 4-regular hypergraph and contains rate R=3/4 constituent convolutional codes with overall constraint length 5. Although the code construction is based on low-complexity codes, the free distance of this construction, computed with the BEAST algorithm, is dfree=120, which is remarkably large.
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15.
  • Hug, Florian (författare)
  • Codes on Graphs and More
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Modern communication systems strive to achieve reliable and efficient information transmission and storage with affordable complexity. Hence, efficient low-complexity channel codes providing low probabilities for erroneous receptions are needed. Interpreting codes as graphs and graphs as codes opens new perspectives for constructing such channel codes. Low-density parity-check (LDPC) codes are one of the most recent examples of codes defined on graphs, providing a better bit error probability than other block codes, given the same decoding complexity. After an introduction to coding theory, different graphical representations for channel codes are reviewed. Based on ideas from graph theory, new algorithms are introduced to iteratively search for LDPC block codes with large girth and to determine their minimum distance. In particular, new LDPC block codes of different rates and with girth up to 24 are presented. Woven convolutional codes are introduced as a generalization of graph-based codes and an asymptotic bound on their free distance, namely, the Costello lower bound, is proven. Moreover, promising examples of woven convolutional codes are given, including a rate 5/20 code with overall constraint length 67 and free distance 120. The remaining part of this dissertation focuses on basic properties of convolutional codes. First, a recurrent equation to determine a closed form expression of the exact decoding bit error probability for convolutional codes is presented. The obtained closed form expression is evaluated for various realizations of encoders, including rate 1/2 and 2/3 encoders, of as many as 16 states. Moreover, MacWilliams-type identities are revisited and a recursion for sequences of spectra of truncated as well as tailbitten convolutional codes and their duals is derived. Finally, the dissertation is concluded with exhaustive searches for convolutional codes of various rates with either optimum free distance or optimum distance profile, extending previously published results.
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16.
  • Hug, Florian (författare)
  • Constructing error-correcting codes with huge distances
  • 2009
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The class of error-correcting convolutional codes is commonly used for reliable data transmission in mobile, satellite, and space-communication. Demanding simultaneously larger capacities and smaller error probabilities, convolutional codes with large free distances are needed. Such convolutional codes are in general characterized by large overall constraint lengths, increasing the complexity of determining the corresponding code properties, such as the free distance. The BEAST – Bidirectional Effcient Algorithm for Searching Trees – will be presented as an alternative, less complex, approach to determine the free distance of convolutional codes. As an example a rate R = 5/20 hypergraph-based woven convolutional code with overall constraint length 67 and constituent convolutional codes is presented. Even though using BEAST, determining the free distance of such a convolutional code is a challenge. Using parallel processing and a common huge storage, it was possible to determine the this convolutional code has free distance 120, which is remarkably large.
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17.
  • Hug, Florian, et al. (författare)
  • Knowledge diversities and group dynamics within international master programs
  • 2010
  • Ingår i: 6:e Pedagogiska Inspirationskonferensen 2010. - 2003-3761 .- 2003-377X. ; 6
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Although international students are allowed to study at Swedish universities since 1985, the Swedish university landscape has undergone a strategic internationalization mainly during the recent few years. With a steadily growing number of international master programs and thereby more international students being part of the Swedish education system, a variety of problems related to cultural-diverse teaching and learning environments and their corresponding methodologies arises. Focusing in particular on knowledge diversity and heterogeneous group work, reasons for facing such problems and suitable approaches will be discussed. Amongst others, more detailed course descriptions, profiling of newly-admitted students, or more individual pre-arrival programs are proposed. Suitable ways how to actively encourage students to interact within cultural-diverse, heterogeneous working groups are discussed, highlighting the necessity of reflection and feedback.
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18.
  • Hug, Florian, et al. (författare)
  • Searching for high-rate convolutional codes via binary syndrome trellises
  • 2009
  • Ingår i: [Host publication title missing]. ; , s. 1358-1362
  • Konferensbidrag (refereegranskat)abstract
    • Rate R=(c-1)/c convolutional codes of constraint length nu can be represented by conventional syndrome trellises with a state complexity of s=nu or by binary syndrome trellises with a state complexity of s=nu or s=nu+1, which corresponds to at most 2^s states at each trellis level. It is shown that if the parity-check polynomials fulfill certain conditions, there exist binary syndrome trellises with optimum state complexity s=nu. The BEAST is modified to handle parity-check matrices and used to generate code tables for optimum free distance rate R=(c-1)/c, c=3,4,5, convolutional codes for conventional syndrome trellises and binary syndrome trellises with optimum state complexity. These results show that the loss in distance properties due to the optimum state complexity restriction for binary trellises is typically negligible.
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19.
  • Hug, Florian, et al. (författare)
  • The BEAST for maximum-likelihood detection in non-coherent MIMO wireless systems
  • 2010
  • Ingår i: [Host publication title missing].
  • Konferensbidrag (refereegranskat)abstract
    • Next generation wireless systems have to be able to efficiently deal with fast fading environments in order to achieve high spectral efficiency. Using multiple-input multiple-output (MIMO) systems and exploiting receive diversity, their spectral efficiency can be greatly increased. Commonly, the channel is estimated via training symbols, before the data detection is carried out based on the previously obtained channel estimate. While this significantly simplifies the process of data detection, it leads in general to suboptimal results. Thereby, a better approach is given by carrying out joint maximum-likelihood (ML) channel estimation and data detection. In this paper, the BEAST — Bidirectional Efficient Algorithm for Searching code Trees — is proposed as an alternative algo- rithm for joint ML channel estimation and signal detection and its complexity is compared with recently published algorithms in this field.
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20.
  • Johnsson, Daniel, et al. (författare)
  • Searching for new convolutional codes using the cell broadband engine architecture
  • 2011
  • Ingår i: IEEE Communications Letters. - 1089-7798. ; 15:5, s. 560-562
  • Tidskriftsartikel (refereegranskat)abstract
    • The Bidirectional Efficient Algorithm for Searching code Trees (BEAST), which is an algorithm to efficiently determine the free distance and spectral components of convolutional encoders, is implemented for the Cell Broadband Engine Architecture, efficiently utilizing the underlying hardware. Exhaustive and random searches are carried out, presenting new rate R=1/2 convolutional encoding matrices with memory m=26 - 29 and larger free distances and/or fewer spectral components than previously known encoding matrices of same rate and complexity. The main result of this paper consists in determining the previously unknown optimum free distance convolutional code with memory m=26.
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21.
  • Zyablov, Victor, et al. (författare)
  • A lower bound on the minimum distance of chained Gallager codes
  • 2009
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Based on the combination of two regular Gallager (Low-Density Parity-Check (LDPC)) codes, we will introduce a new code construction, called Chained Gallager codes. Following Gallager’s method we will derive a lower bound on the normalized minimum distance for the ensemble of Chained Gallager codes. Applying this lower bound on the normalized minimum distance to different transmissions schemes with two parallel and independent channels, the error correcting capabilities will be studied, stressing the advantages of Chained Gallager codes.
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22.
  • Zyablov, Victor, et al. (författare)
  • Chained Gallager codes
  • 2009
  • Konferensbidrag (refereegranskat)abstract
    • The ensemble of regular Low-Density Parity-Check (LDPC) codes introduced by Gallager is considered. Using probabilistic arguments a lower bound on the normalized minimum distance is derived. A new code construction, called Chained Gallager codes, is introduced as the combination of two Gallager codes and its error correcting capabilities are studied.
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