Partial Variable-Gain AF Relay Selection with Outdated Channel Estimates in Spectrum-Sharing Networks

This paper presents an analytical study on the outage probability (OP) of cognitive amplify-and-forward (AF) with underlay spectrum-sharing systems subject to Rayleigh fading. In the underlying scheme, we consider a partial relay selection with outdated channel state information (CSI) and a spectrum-sharing system where the transmit power conditions are controlled by the combined interference power in the primary network and the maximum allowable transmission power at the secondary network. We first derive the end-to-end OP in closed form and then present asymptotic analysis for the high signal-to-noise ratio (SNR). Finally, Monte-Carlo simulations are provided to verify the accuracy of the theoretical analysis.