Outage minimization in fading channels: Optimal power allocation with channel distribution information known at transmitter

This paper revisits the optimal power allocation for outage minimization in the classic point-to-point fading channels with the channel distribution information (CDI) known at the transmitter. The channel state information (CSI) is assumed to be perfectly known at the receiver, but not available at the transmitter. In particular, we consider a finite horizon of N-block transmissions subject to an average power constraint at the transmitter. Although minimizing the time-averaged per-block outage probability over each N-block transmission is shown to be a non-convex problem for a large class of practical fading channels, we show that the globally optimal power allocation is obtainable by a simple one-dimensional search. It is shown that if the average transmit power is above a certain threshold determined by the distribution of the fading channel and the target transmission rate, the uniform power allocation is optimal; otherwise, an on-off power allocation is optimal. Moreover, a suboptimal low-complexity power allocation scheme is proposed, which is shown to be asymptotically optimal as N goes to infinity. Finally, numerical results are provided to validate our analysis.