A kind of quasi-orthogonal space time block code for amplify-and-forward relay networks is analyzed in this paper. At the source, 4 single-antenna users transmit the quasi-orthogonal space time block code matrix. At the relay node, fast maximum-likelihood decoding algorithm is adopted and the decoded symbols are then encoded into quasi-orthogonal code which is transmitted through transmit antenna. At the destination, pair-wise decoding algorithm is utilized. Finally we compare the performance of the quasi-orthogonal space time block code in relay networks with that of the quasi-orthogonal space time block code in traditional communication system. Simulation results show that at the given BER of 10-3, the new code can provide about gain of 4dB and 1 dB comparing with that for the traditional quasi-orthogonal code, respectively. And at the given BER of 10-5, the new code can provide about gain of 4.6dB and 2.6dB comparing with that for the old quasi-orthogonal code, respectively.
Orthogonal code design for MIMO amplify-and-forward cooperative networks