Enhancing Cooperative Diversity Gains in Dual-Hop One-Way/Two-Way AF Relaying Systems: A Fully Opportunistic Role Selection Strategy

In this paper, we establish a three-node cooperative framework, where three nodes compete to transmit their own information to other nodes in an adaptive manner. Motivated by Darwin's “natural selection law” whose essence is “adaptation,” a new opportunistic ROle SElection (ROSE) mechanism is presented, and the cooperative role for each node can be adaptively adjusted based on the instantaneous channel fading environment. We refer to this fully dynamic role selection rule as full-ROSE. Then, the proposed full-ROSE strategy is incorporated into classical one-way and two-way dual-hop amplify-and-forward (AF) relaying systems, and analytic 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 a high signal-to-noise ratio (SNR), which manifests that under both one-way and two-way relaying scenarios, the proposed full-ROSE strategy can boost the system diversity gain relative to a traditional fixed-role configuration, and a higher diversity gain, as well as a superior diversity–multiplexing tradeoff (DMT), 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. Finally, the impacts of node placement and transmit SNR on the system outage performance and ROSE gain are investigated, and insightful discussions are drawn.