Modelling Analysis of Underlay Cognitive NOMA with Near User Assisted in Coordinated Network

In this paper, we consider a communication scenario where non-orthogonal multiple access (NOMA)-based cooperative direct and relay transmission (CDRT) coexists with an underlay cognitive radio network. The decoding results of near user U1 in the secondary network (SN) are divided into success or failure, and their cooperative transmission strategies are formulated, respectively. For the primary network (PN), we define and derive the outage probabilities of the primary receiver PD in two slots. For the SN, we define and derive the outage probabilities of user U1 (in case 1 and 2) in two slots and the user U2 in the second slot. Finally, the exact and closed-form expressions for outage probabilities of all terminal users are given and the numerical results are further presented.