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Factor Graph Transforms

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  • UserProf. Pascal O. Vontobel, Department of Information Engineering, The Chinese University of Hong Kong
  • ClockFriday 29 May 2015, 11:30-12:30
  • HouseLR5, Department of Engineering.

If you have a question about this talk, please contact Dr Ramji Venkataramanan.

Transforms of functions play an important role in many applications, be it for analysis purposes or for computational complexity reasons. For example, the Fourier Transform of a time function immediately tells us if that function is bandlimited or not. Or, Fast-Fourier-Transform-based techniques can be used to efficiently compute the convolution of two discrete-time functions.

Given that factor graphs represent multivariate functions, it is not surprising that transforms play also an important role for factor graphs. In this talk, we first present an example of a factor graph transform that helps in the analysis of the partition function of a factor graph. (Many important quantities can be expressed as the partition function of a factor graph, and so a good understanding of this object and its approximations is a worthwhile endeavor.)

Afterwards, we present an example of a factor graph transform that leads to an efficient implementation of the sum-product algorithm message update rules for certain function nodes. (The sum-product algorithm is at the basis of decoding algorithms for low-density parity-check codes, a class of codes which appears in various telecommunication standards, and so efficient implementations of the sum-product algorithm are highly desirable.)

The talk is planned to be self-contained; basics of factor graphs will be introduced as needed.

BIO: Biography: Pascal O. Vontobel received the Diploma degree in electrical engineering in 1997, the Post-Diploma degree in information techniques in 2002, and the Ph.D. degree in electrical engineering in 2003, all from ETH Zurich, Switzerland. From 1997 to 2002 he was a research and teaching assistant at the Signal and Information Processing Laboratory at ETH Zurich, from 2006 to 2013 he was a research scientist with the Information Theory Research Group at Hewlett-Packard Laboratories in Palo Alto, CA, USA , and since 2014 he has been an Associate Professor at the Department of Information Engineering at the Chinese University of Hong Kong. Besides this, he was a postdoctoral research associate at the University of Illinois at Urbana-Champaign (2002-2004), a visiting assistant professor at the University of Wisconsin-Madison (2004-2005), a postdoctoral research associate at the Massachusetts Institute of Technology (2006), and a visiting scholar at Stanford University (2014). His research interests lie in information theory, data science, communications, and signal processing.

Dr. Vontobel has been an Associate Editor for the IEEE Transactions on Information Theory (2009-2012) and an Awards Committee Member of the IEEE Information Theory Society (2013-2014). Currently, he is an Associate Editor for the IEEE Transactions on Communications, a Distinguished Lecturer of the IEEE Information Theory Society, and a TPC Co-Chair of the upcoming 2016 IEEE International Symposium on Information Theory. He has been on the technical program committees of several international conferences and has co-organized several topical workshops, most recently a workshop at Princeton University on “Counting, Inference, and Optimization on Graphs.” Moreover, he has been three times a plenary speaker at international information and coding theory conferences and has been awarded the ETH medal for his Ph.D. dissertation.

This talk is part of the Signal Processing and Communications Lab Seminars series.

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