This chapter evaluates OP of a cooperative underlay Cognitive radiounderlaycognitive radio network under the joint impact of channel correlation and hardware impairment. We present the analysis and derivation of closed-form expressions of OP at the secondary receiver, which is equipped with two receiving antennas, and exploit the selection combining receiving diversity, over Rayleigh fading channels with correlation between two antenna links. Finally, we provide the Monte Carlo simulations in the integrated simulation tool to verify the derived formulas.