Pre-LNA smart soft antenna selection for MIMO spatial multiplexing/diversity system when amplifier/sky noise dominates

Due to a beamforming capability, Soft Antenna Selection (SAS) techniques have shown great performance improvements over the traditional antenna sub-set selection schemes for Multi-Input and Multi-Output (MIMO) communication systems. A SAS method is basically defined by a pre-processing matrix which is located in RF domain, either before or after the Low Noise Amplifier (LNA). In this paper, we propose a pre-LNA SAS module which is adaptively tuned to maximise the mutual information or the Signal to Noise Ratio (SNR) gain for spatial multiplexing or diversity transmissions, respectively. The SAS optimality is discussed for the two practical cases where either the sky noise or the amplifier noise dominates. We analytically show that the pre-LNA SAS method even outperforms the full-complexity MIMO system for when the number of receive Radio Frequency (RF) chains is greater than or equal to the number of the transmit RF chains. The simulation results verify this claim and also superiority of the proposed scheme to the post-LNA SAS. Copyright © 2010 John Wiley & Sons, Ltd.