AF relaying in underlay spectrum-sharing systems with outdated CSI

In this paper, we study the outage probability of the amplify-and-forward (AF) cognitive relaying in spectrumsharing environments with outdated channel state information (CSI) over Rayleigh fading channels. A selection of the best relay in the secondary system with outdated channel information is considered. We derive a closed-form expression for the tight lower bound on the end-to-end outage probability using the cumulative density function (CDF) approach. Furthermore, the asymptotic behavior of the outage performance is investigated and reveals the diversity order of the underlying scheme. Finally Monte-Carlo simulations are provided to verify the analytical framework.