# Interaction Strictly Improves the Wyner-Ziv Rate-distortion function - Computer Science > Information Theory

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Abstract: In 1985 Kaspi provided a single-letter characterization of thesum-rate-distortion function for a two-way lossy source coding problem in whichtwo terminals send multiple messages back and forth with the goal ofreproducing each other-s sources. Yet, the question remained whether moremessages can strictly improve the sum-rate-distortion function. Viewing thesum-rate as a functional of the distortions and the joint source distributionand leveraging its convex-geometric properties, we construct an example whichshows that two messages can strictly improve the one-message Wyner-Zivrate-distortion function. The example also shows that the ratio of theone-message rate to the two-message sum-rate can be arbitrarily large andsimultaneously the ratio of the backward rate to the forward rate in thetwo-message sum-rate can be arbitrarily small.

Author: ** Nan Ma, Prakash Ishwar**

Source: https://arxiv.org/