A Fully Opportunistic Role Selection Strategy for AF Relaying Systems

A three-node cooperative framework is established, where three nodes compete to transmit their own information to other nodes in an adaptive manner. To this end, a new opportunistic role selection mechanism is presented in which the cooperative role for each node is adaptively adjusted based on the instantaneous channel fading environment. We refer to this fully dynamic role selection rule as full-ROSE. Assuming a dual-hop amplify-and-forward (AF) relaying scenario, closed-form lower and upper bound expressions are derived for the system outage probability. Furthermore, an asymptotic analysis is performed to characterize the system outage behavior at high signal-to-noise ratio (SNR), which manifests that the proposed strategy can boost the system diversity gain relative to traditional fixed role configuration, and a higher diversity gain as well as a superior diversity-multiplexing tradeoff can be achieved. In addition, a new measure, namely, the ROSE gain, is defined to describe the performance improvement of the full-ROSE strategy relative to the fixed role configuration. The impacts of transmit SNR on the system outage performance and ROSE gain are investigated, and insightful discussions are drawn.