  The conflation of cognitive radio (CR) and nonorthogonal multiple access
(NOMA) concepts is a promising approach to fulfil the massive connectivity
goals of future networks given the spectrum scarcity. Accordingly, this letter
investigates the outage performance of imperfect cooperative CR-NOMA networks
under hardware impairments and interference. Our analysis is involved with the
derivation of the end-to-end outage probability (OP) for secondary NOMA users
by accounting for imperfect channel state information (CSI), as well as the
residual interference caused by successive interference cancellation (SIC)
errors and coexisting primary/secondary users. The numerical results validated
by Monte Carlo simulations show that CR-NOMA network provides a superior outage
performance over orthogonal multiple access. As imperfections become more
significant, CR-NOMA is observed to deliver relatively poor outage performance.
