Active noisy feedback

Error exponents for the Gaussian channel with active noisy feedback

Young-Han Kim, Amos Lapidoth, and Tsachy Weissman

We study the best exponential decay in the blocklength of the probability of error that can be achieved in the transmission of a single bit over the Gaussian channel with an active noisy Gaussian feedback link. We impose an expected block power constraint on the forward link and study both almost-sure and expected block power constraints on the feedback link. In both cases the best achievable error exponents are finite and grow approximately proportionally to the larger between the signal-to-noise ratios on the forward and feedback links. The error exponents under almost-sure block power constraints are typically strictly smaller than under expected constraints. Some of the results extend to communication at arbitrary rates below capacity and to general discrete memoryless channels.