Outage Performance of Underlay Cognitive Decode-and-Forward Opportunistic Relaying with Imperfect Channel State Information and Co-channel Interference

The outage performance of decode-and-forward cognitive ratio opportunistic relay (DF CR-OR) systems is investigated over Rayleigh fading environments. We specially consider the case where the systems are impaired by the imperfect channel state information (CSI) between the secondary users and the primary user, and by the co-channel interference (CCI) at secondary relays and destination. We first obtain the exact closed-form expression to outage probability of cognitive systems by considering jointly the impact of the imperfect CSI and the CCI. Secondly, the presented simulation results show that the curves´ slops of outage probability are same for all different CSI or CCI. This indicates that diversity order of the interested cognitive systems is not influenced by the imperfect CSI and the CCI. At the same time, the simulated results also show that the imperfect CSI and the CCI cause the very severe loss in system outage performance even if they do not result in the loss in diversity order.