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Proportional-Fairness Resource Allocation for a Downlink Multicarrier NOMA System

A new resource allocation scheme is proposed for a downlink multicarrier non-orthogonal multiple access (NOMA) system with K users and N subcarriers. The scheme is developed from consideration of an optimization problem of user selection, subcarrier assignment, and power allocation to maximize the sum capacity under a general proportional user fairness constraint. A user selection method is first described based on the achieved capacity-to-fairness-factor ratio of each user at present, where two users with the smallest ratios are paired for NOMA transmission on an available subcarrier. Then, a joint subcarrier assignment and power allocation algorithm is presented for the pair of users for NOMA sum capacity maximization. The above procedure is repeated until all the subcarriers have been assigned to users for transmission. The proposed scheme involves low time complexity of O(N2 + K2) to provide a suboptimal solution to the resource allocation problem. Computer simulation results also show that it achieves better system capacity performance than the conventional orthogonal frequency division multiple access scheme and a related multicarrier NOMA work with every two users having identical fairness factors.