Polynomial Singular Value Decompositions of a Family of Source-Channel Models

In this paper, we show that the conditional expectation operators corresponding to a family of source-channel models, defined by natural exponential families with quadratic variance functions and their conjugate priors, have orthonormal polynomials as singular vectors. These models include the Gaussian channel with Gaussian source, the Poisson channel with gamma source, and the binomial channel with beta source. To derive the singular vectors of these models, we prove and employ the equivalent condition that their conditional moments are strictly degree preserving polynomials.