Efficient message relaying for wireless user cooperation: Decode-Amplify-Forward (DAF) and hybrid DAF and coded-cooperation

Amplify-forward (AF) can be modeled as a way of forwarding soft reliability information extracted directly from the transmit channel, without utilizing the channel code that may well exist in the source-packet. Decode-forward exploits the channel code but forwards the hard-decisions only. These observations motivate the proposition of an efficient new relaying strategy, decode-amplify-forward (DAF). By having the relay perform soft decoding and forward the reliability information at the output of its decoder instead of that from the raw channel, DAF cleverly combines the merits of both AF and DF: soft information representation in AF and coding gain in DF. A hybrid scheme of DAF and coded cooperation (DAF-CC), implemented through simple time-sharing, is further discussed. The information-theoretic achievable rates of these schemes are formulated for channels with binary inputs and Gaussian outputs. Both analysis and simulations confirm that the proposed schemes are capable of considerably better performances than the existing schemes.