A centralized role selection scheme for two-user amplify-and-forward relaying systems

In this paper, an optimal and centralized role selection scheme for two-user amplify-and-forward relaying systems is proposed, where two users compete to transmit their own information to a common destination. Relying on the instantaneous channel conditions, either of the two users can opportunely play the role of an information source and the other user will serve as an amplify-and-forward relay. The proposed framework aims to maximize the received signal-to-noise ratio (SNR) at the destination, which enhances the transmission reliability. In order to reveal the inherent impacts of different link statistics on the system outage behavior, a closed-form lower-bound expression for the outage probability is derived. Moreover, an asymptotic outage analysis is carried out and points out that the high-SNR outage behavior of the proposed scheme is dominated by the user-destination links irrespective of the inter-user link. Our analytical results are corroborated by means of Monte Carlo simulations.