Abstract
This paper presents a resource allocation algorithm based on statistical channel state information for a downlink multicarrier non-orthogonal multiple access (NOMA) system with K users and N subcarriers. The algorithm is developed by solving an optimization problem in terms of user selection, subcarrier assignment, and power allocation for maximizing the expected sum capacity under a proportional user fairness constraint. It operates in an iterative manner and includes two parts at each iteration: 1) user selection; 2) joint subcarrier assignment and power allocation. In the user selection part, two users with the smallest and second smallest achieved expected-capacity-to-fairness-factor ratios at present are paired for NOMA transmission on a subcarrier. In the joint subcarrier assignment and power allocation part, one of available subcarriers is assigned to the pair of NOMA users with appropriate power allocation for maximizing the expected sum capacity of both users. The proposed algorithm can provide a suboptimal solution with low time complexity of O(N2+K2). As compared with the conventional orthogonal frequency division multiple access system, the proposed multicarrier NOMA scheme offers higher expected system capacity with the same order of time complexity under the same proportional user fairness constraint.