On Robustness of Hybrid Digital/Analog Source-Channel Coding With Bandwidth Mismatch

For transmission of memoryless Gaussian sources over channels with additive white Gaussian noise, the tradeoff between the distortion when the channel quality is good versus bad is investigated under the constraint that the distortion is optimal when the channel has the targeted median quality. The problem was proposed by Tian and Shamai, who subsequently proved remarkable achievability results for bandwidth expansion ratios kappa, which are integers or unit fractions, i.e., kappa = 2, 3, 4, ... or kappa = 1/2, 1/3, 1/4, ... Their result is extended here to all kappa >= 2 and kappa <= 1/2 by generalizing the hybrid digital/analog (HDA) scheme of Wilson et al. to the case of bandwidth mismatch. Finally, novel schemes are proposed for 1/2 <= kappa < 1 and 1 < kappa <= 2 achieving nontrivial tradeoffs outperforming all known schemes. These latter schemes rely on another extension of the HDA scheme by Wilson et al., namely, the relaxation of the independence of source and channel input sequences.