DMT analysis of asynchronous OFDM amplify-and-forward cooperative networks

The outage behavior of amplify-and-forward (AF) relaying protocol over an asynchronous cooperative network is examined when orthogonal frequency division multiplexing (OFDM) is used to combat synchronization error among the transmitting nodes. We consider non-orthogonal AF (NAF) and orthogonal
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AF (OAF) protocols, respectively, over a single relay and a two relay cooperative network and analyze the diversity multiplexing gain tradeoff (DMT) in both scenarios. It is proved that, in the limit of code words length, the asynchronous network with the OAF protocol provides the same DMT as of the corresponding synchronous network; however in case of the NAF protocol, it provides the better DMT throughout the range of multiplexing gain and as great as the one of a 2 × 1 multiple input single output channel.