Friendly Jamming Assisted Secure Cooperative Multicasting in Cognitive Radio-NOMA Networks

This paper studies physical layer security (PIS) based secure multicasting to a group of cell-edge users in the presence of a passive eavesdropper. In this view, the base station (BS) hires a pair of users from another multicast group located in its vicinity to perform simultaneous relaying and jamming. The goal is to improve the reception reliability of the weaker users while ensuring minimum interception. The network is modeled using the spectrum efficient CR-NOMA framework whereby, the cell-center group designated as secondary user multicast group (SU-MG) is incentivized with spectrum access opportunity for assisting the cell-edge group viewed as primary user multicast group (PU-MG). A secure cooperative multicast NOMA (SCM-NOMA) protocol is proposed, and comparative performance analysis in terms of secrecy outage probability (SOP) is presented considering different strategies of relay and jammer selection. Numerical results highlight the importance of the joint selection of the best jammer and the best relay and sharing of total power between them for enhancing the SOP performance of the PUMG. Furthermore, the SOP reduces when the selected relay aims to minimize the interception from the eavesdropper rather than maximizing the capacity of the PU-MG.