Comments on 'Channel Coding Rate in the Finite Blocklength Regime': On the Quadratic Decaying Property of the Information Rate Function

Publisher:
Institute of Electrical and Electronics Engineers (IEEE)
Publication Type:
Journal Article
Citation:
IEEE Transactions on Information Theory, 2023, 69, (9), pp. 5528-5531
Issue Date:
2023-09-01
Full metadata record
The quadratic decaying property of the information rate function states that, given a fixed conditional distribution pY|X , the mutual information between the (finite) discrete random variables X and Y decreases at least quadratically in the Euclidean distance as pX moves away from the capacity-achieving input distributions. It is a property of the information rate function that is particularly useful in the study of higher order asymptotics and finite blocklength information theory, where it was already implicitly used by Strassen (1962) and later, more explicitly, by Polyanskiy-Poor-Verdú (2010). However, the proofs outlined in both works contain gaps that are nontrivial to close. This comment provides an alternative, complete proof of this property.
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