Strong functional representation lemma and applications to coding theorems

This paper shows that for any random variables X and Y, it is possible to represent Y as a function of (X, Z) such that Z is independent of X and I(X; Z| Y) ≤ log(I(X; Y)+1)+4. We use this strong functional representation lemma (SFRL) to establish a tighter bound on the rate needed for one-shot exact channel simulation than was previously established by Harsha et. al., and to establish achievability results for one-shot variable-length lossy source coding and multiple description coding. We also show that the SFRL can be used to reduce the channel with state noncausally known at the encoder to a point-to-point channel, which provides a simple achievability proof of the Gelfand-Pinsker theorem. Finally we present an example in which the SFRL inequality is tight to within 5 bits.