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We compare the NOMA users¡¯minimum bit rates under different power allocation policies and NOMA user numbers in Fig. 3, the proposed IP-AO and OPA outperform both EPA and channel state information-based power allocation (CSI-PA) strategy [9] (the allocated power of each user is proportional to the channel gain). The OPA scheme achieves the maximum system bit rate with minimum complexity. Meanwhile, CSI-PA method exacerbates user unfairness and results in suboptimal performance. Specially, the fixed power allocation yields decreased minimum rates with more users, which is due to the total power constraints |