Non-Orthogonal Multiple Access in Spectrum-Sharing Network under Interference Power Constraints

In this paper, we investigate a non-orthogonal multiple access (NOMA) scheme with partial relay selection in underlay cognitive radio networks. We consider a cognitive cooperative relaying setup where a secondary source node communicates with two destination nodes through the help of a single relay node - selected from a set of decode-and-forward (DF) relay nodes - as long as the multiple cognitive transmissions do not compromise the primary network's quality of service (QoS). In this regard, the relay nodes are used to improve the reliability and network coverage of the cognitive network, given the strict power constraints on the cognitive source. Specifically, closed-form expressions for the outage probabilities at both destination nodes are obtained. Moreover, Monte Carlo simulations are provided to assess the accuracy of the proposed analytical framework.