Outage Performance of Underlay CR-NOMA Networks with Detect-and-Forward Relaying

Non-orthogonal multiple access (NOMA) is considered to be one of the promising multiple access techniques for 5G networks. This paper studies a decode-and-forward cooperative underlay cognitive radio NOMA network. Closed-form expressions for the outage probability of two NOMA secondary destination users (D
₁
and D
₂
) are evaluated. Furthermore, optimal power allocation factors for different distances of D
₁
are found to satisfy the outage probability (OP) fairness for both users. Moreover, the OP for NOMA compared to that of conventional multiple access. Finally, the obtained analytical expressions are corroborated by Monte Carlo simulation.