Channel feedback is delayed in all practical wireless systems. Adaptive transmission strategies need to account for this feedback delay in order to be effective. We consider multiple-input single-output systems that perform power control based on a delayed SNR estimate. For perfect channel state information at the receiver (CSIR) and delayed channel state information at the transmitter (CSIT), we derive an expression for the power control function that minimizes outage probability at a constant rate. For imperfect CSIR and delayed CSIT, we derive an upper-bound on outage probability, and an expression for the power control function that minimizes this upper-bound. © 2005 IEEE.