Role Selection Cooperative Systems with Energy Harvesting Relays

In this paper, a three-node energy-harvesting (EH) cooperative system with ROle SElection (ROSE) mechanism, where the cooperative role of each node is dynamically adjusted based on the surrounding wireless fading environment is considered. We first study a benchmark scenario with the fixed role configuration, from which a tight lower bound for the asymptotic outage behavior is derived. For this case, the achievable diversity is limited to two and the system outage behavior at high signal-to-noise ratio (SNR) is affected by the easing-off factor log c₀ together with log(log c₀), with c₀ denoting the source transmit SNR. After that, a dynamic role selection policy is incorporated and the asymptotic analysis shows that the ROSE mechanism can enhance the system diversity order to three, and the decaying law of outage behavior is no longer affected by the log c₀ and log(log c₀) factors. In addition, the power-splitting receiver achieves the same asymptotic outage performance as that of the ideal EH receiver. Our results reveal that the line-of-sight component is crucial to improve the performance of the EH-based ROSE cooperative system, and the role decision with imperfect channel information has a detrimental effect on the system's diversity gain.