Effect of the Imperfect Channel State Information on the Spectrum Sharing Cognitive Relay Networks

In spectrum sharing cognitive relay networks, due to the presence of imperfect Channel State Information (CSI), the interference from the secondary user can be higher than the maximum allowable interference level at the primary user and affect the primary users reliable communication. In order to quantify the impact of the secondary users interference on the primary user, a performance metric termed as interference probability is proposed. The closed-form expressions for interference probability of Opportunistic Relaying (OR) and Selection Cooperation (SC) are derived with imperfect CSI. It is shown that, in terms of the interference probability, the SC is better than the OR. However, the limit interference probability of the OR is identical to that of the SC. Moreover, with imperfect CSI, for both the SC and the OR, increasing the number of relays means a higher interference level on the primary user. Finally, simulation results are presented to verify the analysis.