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This paper investigates the performance of narrowband, slowly-fading, and delay-limited multiple-antenna systems where channel state information (CSI) is available at the transmission end. This situation can arise in time-division duplex (TDD) based two-way systems where channel state estimation can be performed using the signal received from the opposite link. Power control methods which attempt to keep the transmission rate constant at the expense of randomizing the transmit power are considered. It is shown that significant savings in the average transmit power (sometimes on the order of tens of dB) can be expected compared to systems which keep the total transmit power constant. Several practical channel coding examples are illustrated and their bit and frame error rate performance are discussed.