Linear unitary precoders for maximum diversity gains with multiple transmit and receive antennas

In this paper, we analyze the performance of multiple-transmit/receive antenna systems with linear precoders. From the performance of these systems, we deduce design rules for linear precoders. Following the design rules, we prove the existence and derive linear unitary precoders achieving maximum diversity gain. Compared with existing real precoders, the novel unitary precoders offer the potential of larger coding gains. Simulations illustrate that the unitary precoders can achieve more than 1 dB coding gain over real precoders while they perform comparably to repeated transmissions, that consume larger amounts of bandwidth when two or three transmit antennas are utilized.