Antenna selection and power combining for transmit beamforming in MIMO systems

We investigate the transmit beamforming with antenna selection and power combining for multiple antenna systems with practical per-antenna power constraint. We consider that more than one power amplifier (PA) outputs can potentially be combined by using power combiners, such as hybrid combiners, and fed into antennas with stronger channel gains in order to achieve better channel coupling efficiency. The SNR gain of the proposed scheme is analyzed for two different power combining scenarios. For a general number of PAs and transmit antennas, we present an efficient algorithm to find the optimal antenna selection and the power combining vector for multiple-input single-output (MISO) systems, and discuss its extension to general multiple-input multiple-output (MIMO) systems. Numerical results show that the proposed design provides an efficient way to reduce the large SNR loss due to the strong channel imbalance in the MIMO systems.