Resource Allocation in Cognitive Radio Inspired Non-Orthogonal Multiple Access

Abstract

In this paper, we investigate the resource allocation in an underlay cognitive radio network when multiple primary and secondary users are served via multi-carrier non-orthogonal multiple access (MC-NOMA) scheme. Our main objective is to maximize the sum rate subject to a minimum guaranteed rate for the primary users. The performance of the system is highly affected by the power allocation and subchannel assignment for all users. Hence, our optimization problem is formulated as a nonconvex mixed integer non-linear program whose global optimum can be found through a computationally infeasible exhaustive search. To overcome this challenge, we propose an efficient iterative algorithm to jointly optimize subchannel assignment and power allocation, which employs the Hungarian method for subchannel assignment and derives the optimal solution in a closed form for power allocation. Our final solution after convergence indicates that in some subchannels orthogonal multiple access (OMA) scheme is applied instead of NOMA. In other words, the special feature of our proposed solution is that it benefits from both OMA and NOMA schemes to maximize the performance of the system. Simulation results reveal that our proposed solution is very close to the global optimum with considerably less computational complexity and also outperforms the results when the OMA scheme is solely utilized.