On the Performance of Spectrum Sharing Cognitive Relay Networks with Imperfect CSI

In a spectrum sharing scenario, when the channel state information (CSI) of interference links is imperfect, the transmission of the secondary user (SU) may cause a harmful interference on the primary user (PU). To quantify the impact of imperfect CSI on the PU, we present a performance metric termed as interference probability and derive the exact closed-form expression for interference probability of the PU. It is shown that the PU´s interference probability is always equal to 0.75 when the CSI of interference links is imperfect. In order to guarantee the PU´s interference probability below an acceptable value, a back-off power control mechanism is adopted. Then, under the PU´s interference probability constraints, the exact outage probability of partial amplify-and-forward (AF) relay selection scheme in the cognitive relay networks is derived. Finally, numerical results are provided to validate our analysis.