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

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, n/sub T/, is greater than the number of transmit data streams, b, R.W. Heath and A. Paulraj (see Proc. ICC 2001) have proposed a "hard" antenna selection (or switch precoder) which consists in choosing the best b (among n/sub T/) antennas of the transmitter according to a criterion based on the minimum distance. Using the same criterion, we propose 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.