Space-time transmission scheme for asynchronous cooperative communications networks

In this paper, an effective transmission scheme is proposed for asynchronous cooperative networks with two relays. The need for synchronization is obviated by allowing a single relay to be active in each time-slot of the transmission. However, the scheme still achieves a cooperative diversity order of two through some simple operations introduced at the relays while maintaining a single-symbol decoding complexity at the destination. Using the concept of spatial modulation, the scheme is extended for networks with an arbitrary number of relays to offer higher overall throughput as the number of relay increases. The numerical results demonstrate that the bit error rate (BER) performance of the proposed scheme, unlike that of the conventional scheme, does not degrade even when perfect synchronization is not guaranteed.