Distortion exponents for decode-and-forward multi-relay cooperative networks

In this paper, we consider the transmission of a Gaussian signal in a multi-relay cooperative system, where each relay is half-duplex and employs the decode-and-forward relaying protocol. We focus on the analysis of the distortion exponent, which characterizes the high signal-to-noise ratio (SNR) behavior of the end-to-end distortion. Specifically, we investigate the layered source coding with progressive or broadcast transmission. Each transmission scheme is further combined with the repetition-based or relay-selection-based multi-relay cooperation protocol. We derive the distortion exponents of all four cases and illustrate the effect of the bandwidth expansion ratio, number of relays and cooperation protocols on the optimal distortion exponent. We also establish the successive refinability of the diversity-multiplexing tradeoff of the repetition-based and relay-selection-based cooperation protocols in multi-relay cooperative systems.