Full-Diversity Uncoordinated Cooperative Transmission for Asynchronous Relay Networks

Due to the distributed nature of cooperative communications systems, the cooperative signals arriving at the destination may not be perfectly aligned, i.e., the system is inherently asynchronous, and signal coordination among multiple relay nodes is imperative. In this paper, we propose a distributed space–time transmission scheme for a general asynchronous cooperative relay network. The scheme provides asymptotic full cooperative diversity, even when the signals arrive at the receiver asynchronously, which can be achieved by a low-complexity minimum-mean-square-error (MMSE) decision feedback equalizer (DFE) instead of the maximum-likelihood (ML) detector. Furthermore, signal coordination is no longer required, which avoids extra coordinating overhead. The proposed scheme applies for both general amplify-and-forward (AF) and decode-and-forward (DF) cooperative communications networks, such as coordinated multipoint/networked multiple-input–multiple-output (MIMO) systems, distributed antenna systems, and relay architecture for cellular systems. Simulation results confirm our analytical results.