On-the-fly coding for real-time applications
MM '09 Proceedings of the 17th ACM international conference on Multimedia
The error exponent of variable-length codes over Markov channels with feedback
IEEE Transactions on Information Theory
The finite-dimensional Witsenhausen counterexample
WiOPT'09 Proceedings of the 7th international conference on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks
Variations on a theme by Schalkwijk and Kailath
IEEE Transactions on Information Theory
Zero-rate feedback can achieve the empirical capacity
IEEE Transactions on Information Theory
Anytime Reliable Transmission of Real-Valued Information through Digital Noisy Channels
SIAM Journal on Control and Optimization
| Hi-index | 755.02 |
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, it is shown that for end-to-end delay, it is generally possible at high rates to beat the sphere-packing bound for general DMCs - thereby providing a counterexample to a conjecture of Pinsker.