Optimal Power Allocation in Downlink Multicarrier NOMA Systems: Theory and Fast Algorithms

In this work, we address the problem of finding globally optimal power allocation strategies to maximize users sum-rate (SR) as well system energy efficiency (EE) in downlink single-cell multicarrier non-orthogonal multiple access (MC-NOMA) systems. Each NOMA cluster includes a set which well-known superposition coding (SC) combined with successive interference cancellation (SIC) technique is applied among them. By obtaining closed-form expression intra-cluster allocation, show that MC-NOMA can be equivalently transformed virtual orthogonal (OMA) system, where effective channel gain these OMA obtained closed-form. Then, SR and EE maximization problems are solved by using very fast water-filling Dinkelbach algorithms, respectively. The equivalent transformation brings new theoretical insights, discussed throughout paper. extensions our analysis other scenarios, such considering rate fairness, admission control, long-term performance, number future next-generation (NGMA) schemes enabling recent advanced technologies, e.g., reconfigurable intelligent surfaces discussed. Extensive numerical results provided performance gaps between single-carrier (SC-NOMA), OMA-NOMA, OMA.