Sequential coding of correlated sources

We study a generalization of the successive refinement coding problem calle d the sequential coding of correlated sources. In successive refinement sou rce coding one first describes the given source using a few bits of informa tion, and then subsequently improves the description of the same source whe n more information is supplied. Sequential coding differs from successive r efinement in that the second-stage encoding involves describing a correlate d source as opposed to improving the description of the same source. We int roduce the notion of a coupled fidelity criterion to quantify perceived dis tortion in certain applications of sequential coding. We characterize the a chievable rate region far this source coding problem and show that the rate region reduces to the successive refinement rate region when the two sourc es are the same. Then we consider the specific case of a pair of correlated Gaussian sources as an example. We give an explicit characterization that reveals an interesting generalization of a property of successive refinemen t of a single Gaussian source.