Effects of feedback strategies on performances of opportunistic amplify-and-forward relaying

In opportunistic relaying, exchanging information is essential to select the best relay. However, too many information-exchanges may rather impair the system performance due to causing congestion in feedback link as well as increasing overhead. In this paper, we investigate the effects of feedback strategies on performances of opportunistic amplify-and-forward (AF) relaying. We consider four feedback strategies: full channel information feedback (FCI), partial channel information feedback (PCI), FCI with full feedback (FCI-FF), and FCI with threshold based reporting (FCI-TBR). In this paper, we will derive the diversity orders of opportunistic AF relaying with PCI and FCI, respectively, and show that the achievable diversity gain with PCI is just one even though FCI achieves full diversity. Therefore we can conclude that PCI is not suitable for opportunistic AF relaying, even though PCI can rather reduce the feedback information. Based on FCI, we also consider a threshold based reporting (TBR) scheme to reduce the amount of feedback and investigate the outage performance for FCI with and without TBR, respectively. The outage performance is obtained in terms of the threshold and feedback error rate. Numerical results show that FCI-TBR achieves outstanding performance when the feedback error is present. From the results, it is also seen that too many relays rather impair the outage performance even for FCI-TBR with an optimum threshold.