Resource allocation for NOMA-based multicast cognitive radio networks with energy-harvesting relays

This paper studies the problem of joint relay selection and power allocation (J-RS-PA) for non-orthogonal multiple-access (NOMA)-based multicast cognitive radio networks with energy-harvesting (EH) relays. Particularly, the primary and secondary transmitters communicate with their receivers over EH amplify-and-forward relays, with the aim of simultaneously maximizing the network sum-rate, minimizing energy consumption, and satisfying quality-of-service (QoS) constraints. The formulated J-RS-PA problem happens to be non-convex and computationally-intensive. Alternatively, it is solved via a low-complexity solution procedure, which optimally solves the power allocation problem over each relay, and then selects the relay that maximizes the network objective function. Additionally, the proposed solution procedure can be used to tradeoff spectrum- and energy-efficiencies. Simulation results are presented to evaluate the proposed solution procedure, which is shown to efficiently yield the optimal network sum-rate and energy consumption solutions, in agreement with the J-RS-PA scheme (solved via a global optimization package), but with lower computational complexity, while satisfying the QoS requirements at the primary and secondary receivers.