Successive coding of correlated sources

The rate-distortion problem for two-layer coding of a pair (X, Y) of correlated sources is considered. The first layer information enables reconstruction of X within a certain distortion D-X, while reception of both layers additionally enables reconstruction of Y within distortion D-Y. While this problem is a special case of the successive refinement problem, the computation of the rate-distortion region for this scenario is nontrivial. Using a general class of outer bounds to the successive refinement rate-distortion region, the successive coding rate-distortion region for the case where (X, Y) is a jointly Gaussian pair and the distortion measure is squared-error is explicitly characterized.