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TIT
2008

Why Do Block Length and Delay Behave Differently if Feedback Is Present?

13 years 11 months ago
Why Do Block Length and Delay Behave Differently if Feedback Is Present?
Abstract--For output-symmetric discrete memoryless channels (DMCs) at even moderately high rates, fixed-block-length communication systems show no improvements in their error exponents with feedback. This paper studies systems with fixed end-to-end delay and shows that feedback generally provides dramatic gains in the error exponents. A new upper bound (the uncertainty-focusing bound) is given on the probability of symbol error in a fixed-delay communication system with feedback. This bound turns out to have a form similar to Viterbi's bound used for the block error probability of convolutional codes as a function of the fixed constraint length. The uncertainty-focusing bound is shown to be asymptotically achievable with noiseless feedback for erasure channels as well as for any output-symmetric DMC that has strictly positive zero-error capacity. Furthermore, it can be achieved in a delay-universal (anytime) fashion even if the feedback itself is delayed by a small amount. Finally...
Anant Sahai
Added 15 Dec 2010
Updated 15 Dec 2010
Type Journal
Year 2008
Where TIT
Authors Anant Sahai
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