Adam Williamson

I am a former student of the UCLA Department of Electrical Engineering who worked in the Communication Systems Laboratory with Professor Rick Wesel. I graduated in 2014.

Much of my research focused on the benefits of feedback in communication systems. In this feedback work, I investigated how incremental redundancy enables transmission at rates close to capacity with short blocklengths (i.e., in several hundreds of bits rather than several thousand that have traditionally been required for fixed-length block codes). This is important because it reduces the number of symbols required to transmit short messages. I demonstrated several constructions for deterministic coding schemes that surpass the information-theoretic lower bounds on rate at short blocklengths, both for the decision feedback and information feedback settings.

For blocklengths under one hundred bits, it's especially important to account for the latency cost of the stopping rule used with variable-length codes, since transmitting additional parity bits for error detection (e.g., in the form of a CRC) imposes rate loss. One alternative to explicit error-detection that I explored is the Reliability-Output Viterbi Algorithm (ROVA), which determines when to terminate transmission based on the word-error probability of the decoded convolutional code sequence. Due to the rate loss of terminated convolutional codes at short blocklengths, I created the ROVA for tail-biting convolutional codes, called the TB ROVA.

For more details about my feedback work, see this Feedback Overview, as well as the following paper and slides from ISIT 2012:

A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "A Rate-Compatible Sphere-Packing Analysis of Feedback Coding with Limited Retransmissions". IEEE Int. Symp. Inf. Theory (ISIT), Cambridge, MA, USA, July 1 - 6, 2012.
Available at http://arxiv.org/abs/1202.1458. [Slides]

Conference Papers (top)

T.-Y. Chen, A. R. Williamson, and R. D. Wesel, "Asymptotic Expansion and Error Exponent of Two-phase Variable-length Coding with Feedback for Discrete Memoryless Channels". IEEE Int. Symp. Inf. Theory (ISIT), Honolulu, HI, USA, June 29 - July 4, 2014.
K. Vakilinia, T.-Y. Chen, S. V. S. Ranganathan, A. R. Williamson, D. Divsalar, and R. D. Wesel, "Short-blocklength Non-binary LDPC codes with Feedback-dependent Incremental Transmissions". IEEE Int. Symp. Inf. Theory (ISIT), Honolulu, HI, USA, June 29 - July 4, 2014.
T.-Y. Chen, A. R. Williamson, and R. D. Wesel, "Increasing Flash Memory Lifetime by Dynamic Voltage Allocation for Constant Mutual Information". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 10 - 14, 2014. [pdf]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Reliability-based Error Detection for Feedback Communication with Low Latency". IEEE Int. Symp. Inf. Theory (ISIT), Istanbul, Turkey, July 7 - 12, 2013. Available at http://arxiv.org/abs/1305.4560.
T.-Y. Chen, A. R. Williamson, and R. D. Wesel, "Variable-length Coding with Feedback: Finite-length Codewords and Periodic Decoding". IEEE Int. Symp. Inf. Theory (ISIT), Istanbul, Turkey, July 7 - 12, 2013. Available at http://arxiv.org/abs/1301.7464.
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Firing the Genie: Two-Phase Short-blocklength Convolutional Coding with Feedback". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 12 - 16, 2013. [pdf]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "A Rate-Compatible Sphere-Packing Analysis of Feedback Coding with Limited Retransmissions". IEEE Int. Symp. Inf. Theory (ISIT), Cambridge, MA, USA, July 1 - 6, 2012. Available at http://arxiv.org/abs/1202.1458.

Journal Papers (Submitted or Accepted) (top)

A. R. Williamson, M. J. Marshall, and R. D. Wesel, "Reliability-output Decoding of Tail-biting Convolutional Codes", IEEE Trans. Commun, June 2014. Available at IEEE Xplore.
T.-Y. Chen, A. R. Williamson, N. Seshadri, and R. D. Wesel, "Feedback Communication Systems with Limitations on Incremental Redundancy", submitted to IEEE Trans. Inf. Theory. Available at http://arxiv.org/abs/1309.0707.

Talks (top) The following presentations were delivered by the speaker listed in bold.

A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Decision Feedback vs. Information Feedback for Variable-length Coding with Short Blocklengths". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 12, 2014. [abstract]
T.-Y. Chen, A. R. Williamson, K. Vakilinia, and R. D. Wesel, "Increasing Flash Memory Lifetime by Dynamic Mutual Information Regulation". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 11, 2014. [abstract]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Reliability-based Error Detection for Feedback Communication with Low Latency". UCLA Electrical Engineering Annual Research Review, Los Angeles, CA, USA, December 11, 2013.
A. R. Williamson, T.-Y. Chen, K. Vakilinia, T. Zhang, and R. D. Wesel, "Dynamic Voltage Allocation Based on Mutual Information for NAND Flash Memory". UCLA CoDESS Kickoff, September 19, 2013. [Slides]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Reliability-based Error Detection for Feedback Communication with Low Latency". IEEE Int. Symp. Inf. Theory (ISIT), Istanbul, Turkey, July 7 - 12, 2013. Available at http://arxiv.org/abs/1305.4560.
R. D. Wesel, T. Zhang, A. R. Williamson, T.-Y. Chen, and K. Vakilinia, "Dynamic Voltage Allocation Based on Mutual Information for NAND Flash Memory". Non-Volatile Memories Workshop (NVMW), San Diego, CA, March 4 - 5, 2013. [Slides]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "Firing the Genie: Two-Phase Short-blocklength Convolutional Coding with Feedback". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 12 - 16, 2013. [pdf]
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "High Throughput with Low Latency: The Analysis and Design of Rate-Compatible Codes for Gaussian Channels with Feedback". UCLA Electrical Engineering Annual Research Review, Los Angeles, CA, USA, December 4, 2012.
A. R. Williamson, T.-Y. Chen, and R. D. Wesel, "A Rate-Compatible Sphere-Packing Analysis of Feedback Coding with Limited Retransmissions". IEEE Int. Symp. Inf. Theory (ISIT), Cambridge, MA, USA, July 1 - 6, 2012. Available at http://arxiv.org/abs/1202.1458.
R. D. Wesel, T.-Y. Chen, A. R. Williamson, and D. Divsalar, "Feedback for Latency Reduction in the Gaussian Channel". IEEE Inf. Theory and Applications (ITA) Workshop, San Diego, CA, USA, February 6 - 10, 2012. [Abstract]

Posters (top)

A. R. Williamson and R. D. Wesel, "Variable-length Coding with Feedback in Practical Communication Systems". UCLA Engineering Tech Forum, Los Angeles, CA, USA, February 6, 2014. [Poster]
A. R. Williamson and R. D. Wesel, "An Improved Lower Bound on Rate for Variable-length Codes with Active Feedback". North American School of Information Theory, West Lafayette, IN, USA, June 3 - 7, 2013. [Poster]

Resources for Students (top)

en_US.dic: a custom LaTeX dictionary file to aid in spellchecking.
This dictionary includes adjectives, common nouns and proper nouns prominent in the information theory literature, such as "non-asymptotic", "achievability", and "Burnashev". This will eliminate unnecessary red-underlining in your TeX editor. It can also be used with Evernote and other programs that use dictionary files. On my Windows computer, the directory this should be placed in is:
C:\Users\[USERNAME]\TeXworks\dictionaries
sample_bib.bib: a sample LaTeX bibliography file.
This database gives examples of BibTeX-formatted citation entries for a conference paper, journal paper, and submitted manuscript. Many students (and professors!) have trouble formatting references correctly with LaTeX, and it doesn't help that the BibTeX citations in the IEEE Xplore Digital Library are larded with problems. For example, a conference publication may be listed in IEEE Xplore as:

booktitle={Information Theory Proceedings (ISIT), 2012 IEEE International Symposium on},

but this is clunky and incorrect. It should include the proper abbreviations and order:

booktitle={Proc. 2012 IEEE Int. Symp. Inf. Theory (ISIT).

Please take a look at the IEEE Citation Reference to see a list of standard abbreviations and citation examples (and please tell me if any of my examples are incorrect). Then make sure you read the formatted version of the citation in your manuscript to see if your TeX editor made any unexpected changes.
In my sample BibTeX database, I use some @string references to keep from having to re-type an entire journal name/abbreviation for each citation of that journal. For example, IEEE Transactions on Information Theory gets abbreviated as

@string{ IT ="IEEE Trans. Inf. Theory"}

so that in each reference to this journal, you only need to enter the following:

journal= IT,

Submitted (unpublished) manuscripts should not give the name of the journal or conference. Simply write "submitted for publication" for manuscripts that are under review (and include a link to the manuscript on arXiv or elsewhere as necessary). You can do this with the following line in the BibTeX entry:

year={submitted for publication. Available: http://arxiv.org/abs/1312.1024},

For manuscripts that have been accepted, supply the journal name, followed by "to be published". For example,

journal= TCOM,
year={to be published. Available: http://arxiv.org/abs/1312.1024},

Contact Information:

adamroyce - ucla - edu