Outage performance of cognitive relay network with imperfect channel estimation under proactive DF relaying

Spectrum sharing in cognitive radio network helps to improve the spectrum utilization. In underlay spectrum sharing model, the secondary users (SU) are allowed to share the licensed spectrum of the primary user (PU) without degrading the performance of PU significantly. The SU needs to obtain channel state information (CSI) of the channel between its transmitter and primary receiver which may be imperfect. Due to this imperfect CSI, transmission of SU may cause excess interference to the primary receiver. In this paper outage performance of SU in a cognitive relay network (CRN) based on underlay spectrum sharing model using proactive decode-and-forward relaying scheme is studied. We assume that the CSI of the interfering links, i.e. links from both the secondary transmitter and secondary relays to the primary receiver is imperfect. The transmit power of SU is controlled by imposing a scaling factor so as to reduce the excessive interference due to imperfect CSI. A closed form expression for the outage probability of SU in absence as well as in presence of PU interference is also derived over Rayleigh faded channel under the constraint of PU outage and verified through simulation. Further, the effect of PU interference on outage probability of SU has been studied under a PU outage constraint. We highlight the effects of imperfect CSI, interference threshold, number of relays, and the PU interference on the outage probability of SU.