The benefits of using multiple antennas at both the transmitter and the receiver in a wireless system are well established. Multiple-input multiple-output (MIMO) systems enable a growth in transmission rate linear in the minimum of the number of antennas at either end [1][2]. MIMO techniques also enhance link reliability and

The benefits of using multiple antennas at both the transmitter and the receiver in a wireless system are well established. Multiple-input multiple-output (MIMO) systems enable a growth in transmission rate linear in the minimum number of antennas at either end [1], [2]. MIMO techniques also enhance link reliability and improve coverage [3]. MIMO is now entering next generation cellular and wireless LAN products with the promise of widespread adoption in the near future. While the benefits of MIMO are realizable when the receiver alone knows the communication channel, these are further enhanced when the transmitter also knows the channel. The value of transmit channel knowledge can be significant. For example, in a four-transmit two-receive antenna system with independent identically distributed (i.i.d.) Rayleigh flat-fading,