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

This 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 promised achievable diversity order by 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.