Do decode-and-forward relaying protocols beat transmit diversity?

This paper addresses the question whether decode-and-forward relaying protocols can beat transmit diversity with respect to ε-outage capacity. We derive expressions of ε-outage capacity for transmit diversity, decode-and-forward, selective decode-and-forward, and incremental decode-and-forward. We demonstrate that the relaying protocols outperform transmit diversity in certain regions. Decode-and-forward is beneficial over transmit diversity when the relay is located close to the source. For selective decode-and-forward to beat transmit diversity, the relay should be placed between the source and the destination, but not too close to the source. The best performance is achieved by incremental decode-and-forward. The region in which this scheme is beneficial over transmit diversity is large. Moreover, as the region becomes smaller, the outage probability for the source-destination link becomes larger.