Best relay selection with joint effects of hardware impairments and interference constraints

We propose an underlay decode-and-forward cognitive (UDFC) scheme under joint effects of hardware impairments at secondary users and interference constraints at multi primary receivers. In this scheme, the transmit powers of a source node and relays are constrained by interference thresholds of primary receivers in which the best relay is selected has the highest decoding capacity from the source to the destination over Rayleigh fading channels. Contributions show that 1) the performance of the proposed protocol is declined when the hardware impairments occur as well as the number of primary receivers increases, and 2) The proposed protocol is better the conventional direct transmission when the number of cooperative relays increases, and 3) the proposed protocol achieves better performance at a suitable impairment level and optimal location of relays, and finally, the closed-form expressions agree well with the simulation results.