Diversity Multiplexing Tradeoff of Asynchronous Cooperative Relay   Networks
  The assumption of nodes in a cooperative communication relay network operating in synchronous fashion is often unrealistic. In the present paper, we consider two different models of asynchronous operation in cooperative-diversity networks experiencing slow fading and examine the corresponding diversity-multiplexing tradeoffs (DMT). For both models, we propose protocols and distributed space-time codes that asymptotically achieve the transmit diversity bound for all multiplexing gains and for any number of relays. 
R. N. Krishnakumar, N. Naveen and P. Vijay Kumar