Power and Subcarrier Allocation in Downlink NOMA Systems: Equal Power Allocation and DC Programing Approach

Recently Non-Orthogonal Multiple Access (NOMA) has emerged as a suitable candidate for 5G systems due to its high spectral efficiency and potential to support the highly demanded massive connectivity for Future Radio Access networks. The main concept and difference of NOMA is to transmit multiple user's signal on the same sources such as frequency or time and differentiate the user's signals by splitting into power domain. Power allocation and subcarrier assignment are two main issues in NOMA. In this article, for maximization of the system total sum rate a joint subcarrier assignment and power allocation problem is contemplated. Our aim is to improve the system total throughput and also to maintain a high level of fairness between the users. The total bandwidth of the system is split into subcarriers and only two users are allocated to every subcarrier to minimize the complexity of the system. Two methods are investigated for power assignments to users. In the first method total power is distributed equally to sub channels as well as power on each sub channel is equally divided into users on that sub channel, whereas in second method, an algorithm based on Difference of Convex (DC) programing is proposed for power allocation. At last simulation results are observed and compared for the performance of the proposed methods