Extended orthogonal space-time block coding scheme in asynchronous two-way cooperative relay networks over frequency-selective fading channels

In this paper, we propose a new robust closed-loop extended orthogonal space-time block coding (EO-STBC) scheme for two-way four relay networks over frequency selective fading channels with imperfect synchronization. It is a three time slot scheme where the first one is specified for the two terminals while the other two are specified for amplify-and-forward (AF) relays. An orthogonal frequency division multiplexing (OFDM) data structure is employed at the two terminals using cyclic prefix (CP) insertion to combat the effect of multipaths and time asynchronicity. Full spatial diversity with array gain and code rate of 2 over 3 is achieved through applying a simple feedback approach over only two relays. Simulation results are used to show the performance improvements resulting from the proposed system. Furthermore, our scheme uses a simple symbol-wise maximum likelihood (ML) decoder to extract the information data.