Subcarrier and power allocation scheme for downlink OFDM-NOMA systems

In this study, the authors investigate the resource allocation (RA) problem for the downlink orthogonal frequency division multiplexing based non-orthogonal multiple access (OFDM-NOMA) system. The RA problem is decomposed into two subproblems of subcarrier allocation (SA) and power allocation (PA). For the SA, a user grouping based greedy algorithm is proposed under the assumption that power is uniformly distributed among all the selected users. For the PA, the authors propose the iterative water-filling and specific user rate maximising criterion with minimum rate constraints (iterative WF+SURMC-MRC) scheme to jointly consider the PA problem among the selected users on one subcarrier and the PA problem among subcarriers. The simulation results show that the spectral efficiency performance of the proposed iterative WF+SURMC-MRC scheme outperforms those of the (non-iterative) WF+SURMC-MRC scheme and the uniform distribution (UD)+SURMC-MRC scheme. Moreover, the iterative WF+SURMC-MRC scheme has advantages in resisting against the user overloading compared with the (non-iterative) WF+SURMC-MRC scheme.