On the Performance of Opportunistic Relaying Systems With Limited Feedback

In this paper, the outage performance of opportunistic relaying systems under the constraint of limited feedback is investigated. The outage probability for amplify-and-forward (AF) and selective decode-and-forward (DF) relaying with limited feedback are both derived in closed-form expressions. On this basis, the diversity gain of the system is proved to be only two for both AF and selective DF relaying, regardless of the number of participating relays or feedback accuracy, which differs from the full diversity gain achieved by opportunistic relaying with perfect channel state information (CSI). On the other hand, mathematical analysis shows that the outage performance loss can be evaluated in closed form, and the outage probability approaches asymptotically to that of the perfect CSI opportunistic relaying with the increasing accuracy of feedback. With these theoretical results, a feedback method is developed to assign feedback bits within a given outage performance requirement. Simulation results confirm the theoretical analysis.