Combined beamforming with space-time block coding for wireless downlink transmission

The paper proposes a downlink transmission scheme achieving both transmit diversity gain and beamforming gain via combining space-time block coding (STBC) with adaptive beamforming techniques. The beamforming weights of the combined system are optimized in such a way that the virtual channel coefficients corresponding to STBC-encoded data streams, seen at the mobile receiver, are guaranteed to be uncorrelated. Therefore, the diversity order promised achievable by a conventional system with STBC can be obtained completely. At the same time, an additional beamforming gain is achieved by maximizing the received signal-to-noise ratio (SNR) at the mobile receiver. The superiority of the proposed scheme is confirmed by numerical simulation results.