scenario by adopting an amplify-and-forward (AF) relaying method. The end-to-end outage
probability (OP) for secondary users is studied. Then, we compare the OP for the NOMA and
time-division multiple access techniques and demonstrate that the former one outperforms
the latter. Moreover, the proposed AF protocol is compared to the detect-and-forward one.
Finally, the simulation results validate the derived analytical expressions.