On the Gaussian Fading Broadcast Relay Channel With Causal State Feedback

We investigate a typical setup of a heterogeneous network that can be modeled as a fast Rayleigh fading broadcast relay channel with one source (macrocell Base Station), one full-duplex relay (smallcell BS), and two destinations (mobile users). It is assumed that instantaneous channel state information (CSI) is available at the receivers' side, while only a noiseless causal state feedback from the destinations about the source-to-destination channels is available at the relay. We propose a relaying scheme based on a two-stage decode-compress-forward strategy. The essential idea is to let the relay decode the source messages and then forward to the destinations a function of both the decoded messages and the CSI feedback. By characterizing and evaluating the achievable rate region of the proposed relaying scheme, we reveal that non-negligible performance gains over conventional cooperative strategies can be obtained by exploiting CSI feedback at the relay.