A Rotated Quasi-Orthogonal Space-Time Block Code for Asynchronous Cooperative Diversity

The rotated quasi-orthogonal space-time block code (RQSTBC) for asynchronous cooperative diversity is proposed in this paper. The source selects half of the symbols from a signal constellation set and the other half of them from that constellation rotated with the optimum angle. Meanwhile, it constructs orthogonal frequency division multiplexing (OFDM) frames to counterbalance time delays of the signals. Then, relays create the frequency domain quasi-orthogonal space-time block transmitted signals matrix in such a way that its items are staggered to take on the Jafarkhani code structure or time-reversion of it. These three stages let the received signals at the destination take on RQSTBC structure with diversity order 4, which results in the fast symbol-pair-wise maximum likelihood (ML) decoder. Simulation results have shown that the proposed scheme outperforms the other asynchronous cooperative diversity schemes considered in this paper.