Outage probability for MISO fading channels with imperfect feedback

An optimal transmission strategies in terms of minimum outage probability for a fading channel with multiple transmit antennas and a single receive antenna is studied. We consider two cases of imperfect channel state information (CSI) feedback, mean feedback and covariance feedback. In both cases the optimum strategies are shown to be transmission of multiple data streams to the same directions as when maximizing the ergodic channel capacity, but with different power allocation strategies related to the target rate. Moreover, the accuracy of the feedback CSI affects significantly the achievable outage capacity in the case of mean feedback; the outage capacity achieved in the case of covariance feedback is much lower than that in the case of mean feedback. Therefore, accurate tracking of the instantaneous CSI is essential in maximizing outage capacity.