Performance analysis of relay selection schemes in underlay cognitive networks with imperfect channel state information

Cognitive Radio (CR) aims to improve spectrum utilization by allowing unlicensed users to access the licensed spectrum and to coexist with primary user (PU) while respecting the PU´s restrictions. An interesting case to consider in underlay CR is when the channel state informations (CSI) of the links between secondary users (SUs) or between SUs and PU are imperfect. In fact, due to feedback or scheduling delays, in practice, the relay and/or the source node can have outdated channel state information. This outdated information will cause a performance degradation. In this paper, its impact on relay selection schemes and PU are investigated. To evaluate the impact of imperfect CSI on the secondary network, closed form expressions of the bit error rate (BER), the outage probability and the ergodic capacity are derived. 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.