Outage performance of DF relay selection schemes with outdated CSI over Rayleigh fading channels

Abstract

In this study, the authors first propose two protocols, namely the opportunistic relay (OR) priority and the direct retransmission (DR) priority, based on the reactive and proactive OR selection schemes, respectively. Then, they investigate the outage performance of these protocols with outdated channel state information (CSI) and derive the exact closed-form expressions of the outage probabilities of all the considered scenarios based on the decode-and-forward (DF) protocol. In the high signal-to-noise ratio regime, the authors analyse the asymptotic outage behaviour. In addition, based on the asymptotic analysis, the diversity orders of all the schemes mentioned above are derived. Theoretical analysis and simulation results show that (i) the outage performance of the DR priority is better than that of the OR priority; (ii) the outage performance of the reactive OR selection is better than that of the proactive OR selection in the same scenario; (iii) the diversity orders of all the considered schemes will be reduced to 2 when the CSI is outdated; (iv) the outage performance will be decreased substantially in the case that the channel correlation coefficient has only a little reduction.