Erasure Entropy

Sergio Verdú, Tsachy Weissman

Abstract: We define the erasure entropy of a collection of random variables as the sum of entropies of the individual variables conditioned on all the rest. The erasure entropy rate of a source is defined as the limit of the normalized erasure entropy. The erasure entropy measures the information content carried by each symbol knowing its context. In the setup of a source observed through an erasure channel, we offer an operational characterization of erasure entropy rate as the minimal amount of bits per erasure required to recover the erased information in the limit of small erasure probability. When we allow recovery of the erased symbols within a prescribed degree of distortion, the fundamental tradeoff is described by the erasure rate-distortion function which we characterize. When no additional encoded information is available, the erased information is reconstructed solely on the basis of its context by a denoiser. Connections between erasure entropy and discrete denoising are also explored