Resolvability in Eγ with Applications to Lossy Compression and Wiretap Channels

We study the amount of randomness needed for an input process to approximate a given output distribution of a channel in the $E_γ$ distance. A general one-shot achievability bound for the precision of such an approximation is developed. In the i.i.d.~setting where $γ=\exp(nE)$, a (nonnegative) randomness rate above $\inf_{Q_{\sf U}: D(Q_{\sf X}||π_{\sf X})\le E} \{D(Q_{\sf X}||π_{\sf X})+I(Q_{\sf U},Q_{\sf X|U})-E\}$ is necessary and sufficient to asymptotically approximate the output distribution $π_{\sf X}^{\otimes n}$ using the channel $Q_{\sf X|U}^{\otimes n}$, where $Q_{\sf U}\to Q_{\sf X|U}\to Q_{\sf X}$. The new resolvability result is then used to derive a one-shot upper bound on the error probability in the rate distortion problem, and a lower bound on the size of the eavesdropper list to include the actual message in the wiretap channel problem. Both bounds are asymptotically tight in i.i.d.~settings.

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