Titre: Quasi-cyclic LDPC codes and efficient hardware implementations
Conférencier: Sébastien Roy , Université de Sherbrooke
Lieu: Université du Québec à Montréal, Pavillon Kennedy, PK-5115 ,
Date et heure: mercredi le 19 février 2014 de 13:30 à 16:00

Résumé: This presentation constitutes an overview of research efforts over the last 10 years focusing on quasi‐cyclic LDPC codes (QC‐LDPC). The research is of a somewhat fundamental nature, but considers hardware implementation issues as a priority. Some LDPC codes are known to approach Shannon capacity within a fraction of a dB. However, the most powerful LDPC codes are typically unstructured or random, which leads to significant hardware implementation difficulties. Another well‐known class of Shannon‐capacity approaching codes is turbo codes. The latter are characterized by very simple encoding (convolutional encoders) and complex decoding (MAP or SOVA decoders). Generally, LDPC codes espouse the opposite pattern: complex encoding and somewhat simpler decoding (belief‐propagation and bit‐flipping). It was first demonstrated that a certain family of QC‐LDPC codes with double‐diagonal structure could greatly simplify encoding, making it simpler and faster than belief‐propagation decoding. Furthermore, a construction method for such codes was devised leading to desirable fundamental properties, namely good performance in the waterfall region of the bit error rate (BER) curve, and no error floor down to 10^(‐10). Various hardware implementations were also proposed for decoding, based on variants of the canonical belief propagation technique. Also, the so‐called "joint row‐column" decoding algorithm was developed, leading to faster convergence and improved BER performance with respect to standard belief propagation. As a further development based on the QC‐LDPC framework, families of codes were devised which allowed adaptive code lengths and code rates. In other words, it became possible to have the same simple codec circuitry support codes with different rates and lengths, yet maintaining near optimal BER behaviour across all configurations. Applications of such families of codes will be discussed, including ARQ (automated repeat request) schemes, MIMO relay systems, and cryptography.

Note biographique: Prof. Sébastien Roy received the B.Sc. and M.Sc. degrees in electrical engineering from Laval University, Québec, QC, Canada, in 1991 and 1993, respectively, and the Ph.D. degree from Carleton University, Ottawa, ON, Canada, in 2000. He is currently a Full Professor with the Department of Electrical and Computer Engineering, Sherbrooke University, where he is pursuing research in the system‐level and implementation aspects of signal processing for communications as well as space‐ time processing and space‐time coding. From 2000 to 2002, he was a Natural Sciences and Engineering Research Council of Canada (NSERC) Postdoctoral Fellow at Laval University. He has also been active in industrial consulting and was involved in the organization of several international conferences. In 2007, 2009, and 2011, he was invited professor at l'École Nationale Supérieure de Sciences Appliquées et de Technologie (ENSSAT), Lannion, France. He received multiple teaching awards and in 2007 received the award for excellence in technology transfer from the strategic network on Systems and Technologies for Advanced Communications (SYTAcom). Dr. Roy was also awarded the award for Post‐Graduate Research Excellence from the Canadian Institute for Telecommunications Research in 2000.

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