A new converse in rate-distortion theory

This paper shows new finite-blocklength converse bounds applicable to lossy source coding as well as joint source-channel coding, which are tight enough not only to prove the strong converse, but to find the rate-dispersion functions in both setups. In order to state the converses, we introduce the d-tilted information, a random variable whose expectation and variance (with respect to the source) are equal to the rate-distortion and rate-dispersion functions, respectively.