摘要
In this paper, we propose user grouping, subcarrier allocation, and bit allocation schemes in multicarrier nonorthogonal multiple access (NOMA) systems on downlink beamforming to reduce the total transmit power while considering the data-rate and the error-rate constraints of practical modulation types. Power control is also considered. In this system, each subcarrier can be assigned to multiple users for data transmission. Each subcarrier is allocated to a cluster that contains groups of two users for data transmission. A subset of subcarriers is assigned to the same cluster for sharing. The system is based on orthogonal frequency division multiple access (OFDMA), in which a primary user (PU) is more important than a secondary user, and we ensure that all assigned subcarriers transmit data to the PU in the system. In the proposed schemes, the user-grouping operation is performed first and the subcarrier allocation along with the bit loading and power assignment are performed subsequently based on the user-grouping results. The simulation results obtained using the proposed schemes in conjunction with the nonorthogonal multiple access to allocate bits, subcarriers, and transmit power show that the proposed schemes outperform the conventional OFDMA system in terms of transmit power.