Soft vs. hard antenna selection based on the minimum distance for MIMO systems

Abstract : Assuming that Channel State Information (CSI) can be available at the transmitter, we provide a simplified representation of Multi-Input Multi-Output (MIMO) systems and derive a new precoder which maximizes the smallest distance between the received symbols. When the number of transmit antennas nt is greater than the number of transmit data streams b, Heath and Paulraj have proposed a ”hard” antenna selection (or switch precoder) which consists in choosing the best b (among nt) antennas of the transmitter according to the criterion based on the minimum distance. Using the same criterion, we propose in this paper a ”soft” (or linear) precoder that performs power allocation among the transmit antennas. Comparisons in term of Bit Error Rate (BER) between switch and linear precoders are performed considering b=2 independent data streams, a QPSK modulation and the Maximum Likelihood (ML) receiver.