Cascade, Triangular, and Two-Way Source Coding With Degraded Side Information at the Second User

In this paper, we consider the cascade and triangular rate-distortion problems where the same side information is available at the source node and user 1, and the side information available at user 2 is a degraded version of the side information at the source node and user 1. We characterize the rate-distortion region for these problems. For the cascade setup, we show that, at user 1, decoding and rebinning the codeword sent by the source node for user 2 is optimum. We then extend our results to the two-way cascade and triangular setting, where the source node is interested in lossy reconstruction of the side information at user 2 via a rate limited link from user 2 to the source node. We characterize the rate-distortion regions for these settings. Complete explicit characterizations for all settings are given in the quadratic Gaussian case. We conclude with two further extensions: a triangular source coding problem with a helper, and an extension of our two-way cascade setting in the quadratic Gaussian case.