Extended orthogonal space-time block coding scheme for asynchronous cooperative relay networks over frequency-selective channels

In this paper, we present a new robust scheme for use in asynchronous cooperative networks over frequency-selective channels through using three and four relay nodes. Based on extended orthogonal space-time block coding (EO-STBC), we have presented a direct quantized feedback approach that can achieve full cooperative diversity and array gain with unity code rate over each hop. In this scheme, we have employed orthogonal frequency division multiplexing (OFDM) type pre-coding at the source node to combat multipath fading and timing errors from relay nodes by using cyclic prefix insertion for the broadcasted and relayed signals. To reduce the feedback overhead significantly we have proposed a quantized group feedback approach which can enhance the system performance. Simulation results show that the proposed scheme yields a significant improvement in bit error rate performance over the previous scheme that has been implemented over two relays and uses a very simple symbol-wise maximum-likelihood decoder.