Abstract
In this paper, the sub-channel assignment (SA) problem is investigated in downlink non-orthogonal multiple access (NOMA) systems. An efficient low complexity SA algorithm is proposed to enhance both the user data rate and total sum-rate in downlink NOMA systems. The proposed SA algorithm is a user-oriented greedy-based algorithm that uses the average of the channel gains per user as a low computational complexity parameter to measure the channel quality of the user. The proposed SA mechanism is based on the lowest channel quality user first concept. The simulation results demonstrate that the proposed SA algorithm can achieve significant enhancement in the total sum-rate, outage probability, and user fairness compared to the existing algorithms. Besides, the proposed SA algorithm can improve the performance of NOMA systems as the number of users increases.