Advances in Protograph-Based LDPC Codes and a Rate Allocation Problem

Speaker: Sudarsan V.S. Ranganathan
Affiliation: Ph.D. Candidate - UCLA

Abstract:  The talk consists of three parts. The first part focuses on a class of modern channel codes known as protograph-based low-density parity-check (LDPC) codes. Also known as protograph LDPC codes, these error-correcting codes have enabled communication systems of the past fifteen years to achieve very high throughputs. The first part of the talk provides a new design method based on an upper bound on minimum distance to obtain rate-compatible, protograph quasi-cyclic (QC) LDPC codes called Protograph-based Raptor-like LDPC codes (PBRL codes). A major contribution here is a very-low-complexity PBRL design algorithm that is provably efficient. We present codes that out-perform those currently proposed for the 5G standard.

The second part of the talk continues the focus on protograph LDPC codes, exploring how the decoding complexity of PBRL codes can be reduced and whether the extending structure that provides rate-compatibility to a PBRL code is optimal or not. This part also considers the problem of design of PBRL codes for any increment ordering. The degree-1 extending structure leads naturally to the design of PBRL codes that decode efficiently even when increments arrive out-of-order.

Finally, the talk turns to communication theory and tackles a rate allocation problem previously explored in literature, but with an important twist. Consider a cross-layer coding scheme with packet-level erasure coding and physical-layer channel coding. It is known from previous work that some erasure coding is necessary even in the limit of large physical-layer codeword block-lengths if the physical-layer fading channel does not provide diversity that grows with block-length. However, is erasure coding still required in the limit of large block-lengths if the physical layer allows for diversity to grow with block-length? The theoretical answer turns out to be a resounding “no” in the case of Rayleigh fading that allows diversity to increase linearly with block-length.

Biography:  Sudarsan V. S. Ranganathan received the bachelor’s degree in electronics and communication engineering from Anna University, Chennai, India, in 2012, and the master’s degree in electrical engineering from UCLA in 2014. He is currently a Ph.D. candidate working with Professor Richard Wesel in the Department of Electrical and Computer Engineering at UCLA. His research interests include coding and information theory, communication systems, and combinatorics. His experiences include two internships at Broadcom Corp., Irvine, CA, USA, during the summers of 2014 and 2015. He was a recipient of the Best Poster Award at the 2015 IEEE Communication Theory Workshop.

For more information, contact Prof. Richard D. Wesel ()

Date(s) - Nov 30, 2018
1:00 pm - 3:00 pm

E-IV Tesla Room #53-125
420 Westwood Plaza - 5th Flr., Los Angeles CA 90095