Combining transmit beamforming and orthogonal space-time block codes by utilizing side information

Recently, efficient space-time codes have been developed that achieve a large portion of the capacity available in communication systems employing multiple transmit and receive antennas. These codes are designed under the assumption that the transmitter has no knowledge about the channel. In this work, on the other hand, we consider the case when the transmitter has partial, but not perfect, knowledge about the channel and how to improve the code so that this fact is taken into account. A transmit scheme is proposed that combines the benefits of conventional beamforming with those given by orthogonal space-time block codes. Simulation results using four transmit antennas demonstrate significant gains.