Resource Optimization for the Non-Orthogonal Multiple Access System in Green Mobile Networks

Non-orthogonal multiple access (NOMA) as one of the key techniques is nominated in new generation of mobile networks that can improve spectral efficiency by using the successive interference cancellation (SIC) method. By this method, users can use a shared channel. Optimal use of spectral and power resources as well as efficient users clustering are important aspects of green NOMA communication networks. In this paper, we assume different users based on their channel gains are dispersed in three near, middle, and far areas to the base station in a cell. To avoid interference and imperfect SIC at the use of NOMA benefits simultaneously, we consider a scenario including grouping of three users. Saving spectral and power resources is the feature of the green NOMA scenario. In the following, with the aim of optimal resource allocation in the NOMA cellular network, we propose the optimization problem of power allocation coefficients to users under increasing the overall system throughput. Power consumption can be optimized by properly allocating power to the base station and users, and with a certain power, can provide a desirable efficiency in the cellular network. To find the optimal power allocation coefficients to users, we prove that the optimization problem is concave/convex, then we apply Lagrangian and KKT conditions. According to the achieved results, the proposed scheme provides a 6.97% improvement in low SNRs and a 1% improvement in high SNRs compared to NOMA with constant power coefficients in terms of the sum capacity.