Optimal Sum-Rate Maximization in a NOMA System with Channel Estimation Error

Non-Orthogonal Multiple Access (NOMA) has recently been conceived as a new technology for 5G cellular communication which has the potential to provide higher throughput than conventional orthogonal multiple access. In this paper, we deal with sum -rate maximization of a downlink NOMA based system in the presence of channel estimation error which is a more practical scenario, with user's QoS and total BS power constraints. By analyzing KKT conditions, a closed form solution for optimal power allocation aiming to maximize sum -rate is derived. Simulation results depict that in terms of sum -rate, NOMA system outperforms conventional orthogonal multiple access (OMA) systems and the gain of NOMA increases with users.