The Cutoff Rate and Other Limits: Passing the Impassable
Speaker: Richard Blahut, University of Illinois at Urbana-Champaign
Department: Electrical Engineering
Location: Engineering Quadrangle B205
Date/Time: Thursday, December 12, 2013, 4:30 p.m. - 5:30 p.m.
The evolution of modern communication systems over the past sixty-five years can be viewed as a progress along the code rate axis, starting from rates close to zero and finally reaching rates almost equal to channel capacity. The rates of communication codes, early on, approached and passed the critical rate, then approached and passed the impassable cutoff rate, and finally came ever closer to the channel capacity. Decoders in these three regimes were predominantly spherical distance decoders, then sequential decoders, then iterative decoders, respectively. Much of this progress can be understood, in hindsight, by revisiting the channel reliability function, and we will attempt to do so. The recently introduced polar codes will be described, assuming that the timing of history were different, as they might have been seen as a bridge leading from sequential methods of decoding to iterative methods of decoding.