User-Pairing based Non-Orthogonal Multiple Access (NOMA) System

Non-orthogonal multiple access (NOMA) is a promising multiple access scheme for next generation wireless networks. This paper investigates the sum rate maximization problem for NOMA system over a frequency selective fading channel with its users being paired according to their channel powers. A hierarchical power allocation process is proposed, whereby the users are divided into two groups such that a closed form power allocation solution can be applied. This divide-and allocate approach is repeated until all users are allocated with a transmission power. The proposed architecture facilitates a large number of users for NOMA system. Simulation results show that the proposed scheme achieves comparable performances to the optimal one based on numerical solution, and outperforms other approaches.