Distributed space-time codes with relay preprocessing for low SNR source-relay links

In this work, we consider a network formed by a single source-destination pair and multiple cooperating relays. For such networks, in most of the previously proposed schemes, the relays that can decode the source message correctly are allowed to retransmit. Although this is a reasonable relaying strategy in the high SNR regime, it suffers in low SNR ranges where the number of relays that can successfully decode the source message can be small. We propose to use an appropriate mapping of the noisy receptions at the relays followed by a distributed space-time code. The proposed schemes outperform the well-known amplify-and-forward and decode-and-forward strategies.