The Impact of Imperfect Channel State Information on the Performances of Relay Selection Schemes in Underlay Cognitive Networks

Relay assisted cognitive radio is a promising technology that allows wireless systems to sense the environment, learn from previous experience and improves spectrum utilization by allowing unlicensed users to access the licensed spectrum. Studies of cognitive radio were mostly assuming a perfect channel state information (CSI). This assumption is usually unrealistic in practice because of the feedback errors or scheduling delays, where transmitting node can have outdated channel state information. This aspect leads to a performance degradation of the secondary and primary systems. To quantify the impact of imperfect CSI on the secondary users (SUs) as well as the primary user (PU), we derive in this paper the exact closed form expression for the outage probability, the bit error rate and the ergodic capacity of the SUs for two different relay selection schemes proposed herein. Additionally, we investigate how harmful imperfect CSI can be on the PU's side. The theoretical results obtained in this work are confirmed through simulations.