In this article, a joint user pairing and secure resource allocation scheme for cognitive radio inspired nonorthogonal multiple access (CR-NOMA) femtocells in the presence of a jammer base station (JBS) is proposed. In the considered CR-NOMA-based femtocells, femto base stations (FBSs) serve their femto mobile station (FMS) by sharing the resource block (RB) with macromobile stations (MMSs), while the JBS in each femtocell secures the data rate of a weak user from the eavesdropping capability of the strong FMS. The strong FMS intercepts the data rate of the weak FMS using a successive interference cancellation technique to decode their own data as per the NOMA principle. The weak FMS protects its data from the strong eavesdroppers through the JBS. The JBS generates artificial noise to confuse the strong eavesdroppers. The problem of the joint user pairing and resource allocation is formulated as an optimization problem, whose main goal is to maximize the secure sum rate of the FMS while guaranteeing the secure data rate of the weak FMS and MMS. For RB allocation, CR at the FBS senses the best RB for its FMS using the Greedy approach. To optimize the power of the FBS and JBS, a successive convex approximation scheme with a low complexity is applied. Simulation results show that our proposed scheme provides an improvement in the secure sum rate of the FMS in comparison to the conventional NOMA and preexisting orthogonal multiple access schemes.
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