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Home Events Events Archive 2014 Reliability-output Decoding and Low-latency Variable-length Coding Schemes for Communication with Feedback

Reliability-output Decoding and Low-latency Variable-length Coding Schemes for Communication with Feedback

— filed under:

  • PhD Defenses
When Apr 21, 2014
from 10:00 AM to 12:00 PM
Where Engr. IV Building, Maxwell Room 57-124
Contact Name
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Adam Williamson

Advisor: Prof. Richard Wesel



This talk focuses on the short-blocklength performance of coded communication systems with feedback. We demonstrate two deterministic coding schemes using tail-biting convolutional codes that can deliver rates surpassing the information-theoretic lower bound at short blocklengths. The first scheme, a reliability-based retransmission scheme using decision feedback, requires only a single bit of feedback (ACK/NACK) after each decoding attempt. In contrast, our information-feedback scheme employs two-phase incremental redundancy and uses feedback of the received symbols to confirm or reject the decoder's tentative estimate. We then discuss implications of these schemes when used in practical systems, namely the performance when decoding is limited to packets instead of individual symbols.

For the decision-feedback scheme, we present a novel reliability-output decoding algorithm for tail-biting convolutional codes, based on the reliability-output Viterbi algorithm (ROVA) for terminated convolutional codes. Whereas terminated convolutional codes suffer from a rate penalty at short blocklengths, tail-biting convolutional codes are throughput-efficient and suitable for used in low-latency hybrid ARQ schemes. This talk makes connections to recent work in finite-blocklength information theory and also describes how feedback is used in modern communication standards, such as 802.11 and 3GPP.


Adam Williamson is a PhD candidate in the Electrical Engineering Department at UCLA, where he is a member of the Communication Systems Laboratory. He received the 2013 PhD Preliminary Exam Award for the Signals and Systems area. Adam completed a master’s degree in Electrical Engineering from UCLA in 2012. He received bachelor’s degrees in Electrical & Computer Engineering, Applied Math, and Physics, in 2008, all from the University of Rochester.

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