Sum-Rate Maximization of NOMA Systems Under Imperfect Successive Interference Cancellation

This letter addresses the sum-rate maximization for a downlink non-orthogonal multiple access (NOMA) system in the presence of imperfect successive interference cancellation (SIC). We assume that the NOMA users adopt improper Gaussian signaling (IGS), and hence derive new expressions of their rates under residual interference from imperfect SIC. We optimize the circularity coefficient of the IGS-based NOMA system to maximize its sum-rate subject to quality-of-service requirements. Compared to the NOMA with proper Gaussian signaling, simulation results show that the IGS-based NOMA system demonstrates considerable sum-rate performance gain under imperfect SIC.