Events Calendar

Failures of Iterative Decoders

Speaker: Shashi Kiran Chilappagri,
University of ArizonaAbstract: Low-density parity-check (LDPC) codes have been the focus of much research in the last decade due to their capacity approaching performance even when decoded with low-complexity algorithms. The message passing algorithms to decode LDPC codes are iterative in nature and work on the Tanner graph representation of the code. While these algorithms are optimal when the underlying graph is a tree, they exhibit surprisingly good performance on loopy graphs. The sub-optimality of these algorithms, however, manifests in the low noise regime leading to a abrupt performance degradation known as the error floor.In this talk, we provide an overview of the recent developments in understanding the error floor phenomenon. For the special case of the Gallager A algorithm, we analyze the trapping sets (the sub-graphs that lead to decoding failures) and present a combinatorial characterization of the underlying topological structure of these sub-graphs. We present tight upper and lower bounds on the guaranteed error correction capability of column-weight-three codes under the Gallager A algorithm. We also show how the knowledge of trapping sets can be used for performance estimation as well as code design.Biography: Shashi Kiran Chilappagri obtained his B.Tech and M.Tech degrees from the Indian Institute of Technology, Madras in 2004 and Ph.D. from the University of Arizona, Tucson in 2008, all in electrical engineering. He is currently a Research Engineer at the University of Arizona. His research interests include coding theory, graph theory as well as application of coding theory to inference problems in biology.Host: Alex Dimakis, dimakis@usc.edu, EEB 532, x09264

Location: Hughes Aircraft Electrical Engineering Center (EEB) - 539

Audiences: Everyone Is Invited

Contact: Gerrielyn Ramos