In wireless cooperative networks, the asynchronism between the relays can be a source of diversity which is similar in its essence to the multipath diversity of frequency selective channels. In this context, an asynchronous two-relay cooperative wireless network using the Decode-and-Forward protocol is studied. Two strategies for relay coding are studied: independent coding and repetition coding. The outage probability in the high Signal to Noise Ratio (SNR) regime is derived for different relative delays between the two relays. An optimization of the power allocation is given to improve the network performance. We show that the use of independent coding by the asynchronous relays gives better outage probability performance.