Strict Suboptimality of Selection Amplify-and-Forward Relaying Under Global Channel Information.

Selection amplify-and-forward (SAF) relaying, which has been shown to be optimal under the constraints of localized channel information at the relays and a constant relay power allocation (PA) template, is shown to be globally strictly suboptimal. A necessary condition for the outage optimality of the SAF PA, and an exponentially vanishing upper bound on the probability of the SAF optimality are derived. [ABSTRACT FROM AUTHOR]