Optimal power allocation in opportunistic relaying with outdated CSI

In this paper, we study the impact of outdated channel state information (CSI) on a cooperative system based on opportunistic relay selection (ORS). The study is carried out by obtaining an analytical expression for the outage probability, defined as the probability that the instantaneous mutual information is lower than a target rate. Besides, we propose the optimal power allocation aimed at minimizing the outage probability when the available CSI is subject to impairments. As shown in the paper, the proposed strategy provides significant gains when compared with uniform power allocation.