Optimal Power Allocation Scheme for Non-Orthogonal Multiple Access with α-Fairness

In this paper, the optimal power allocation scheme is investigated for sum rate maximization of non- orthogonal multiple access (NOMA) with adaptive rates and α-fairness. Compared to the existing fairness NOMA models, α-fairness can only utilize a single scalar to achieve different user fairness levels. Specifically, the power allocation problem is first formulated to maximize the instantaneous sum rate with α-fairness, where user rates are adapted according to the instantaneous channel state information (CSI). Then, a simple alternate algorithm is proposed to solve the Karush-Kuhn Tucker (KKT) conditions of the formulated power allocation problem. Analytical results demonstrate that the proposed algorithm converges and yields the optimal solution. Numerical results reveal that, at the same fairness level, NOMA significantly outperforms the conventional orthogonal multiple access (MA)