Secrecy Rate Maximization in Relay-Assisted NOMA with Imperfect SIC

Non-orthogonal multiple access (NOMA) has emerged as an enabling solution for 5th generation and beyond networks, but the often-neglected issues due to successive interference cancellation (SIC) based decoding might seriously hamper its performance. In this paper, we study a downlink NOMA system with cooperative half-duplex relaying with imperfect SIC, where the base station is communicating with two untrusted users with the aid of a trusted decode-and-forward relay while also considering the availability of direct links from the source. An optimization problem is formulated for maximizing the secrecy rate of the near user while fulfilling the quality-of-service requirements of the far user. The optimal power allocation solution is derived while considering the impact of SIC error. The simulation results illustrate the exactness of the theoretical analysis alongside insightful discussions to investigate the impact of imperfect SIC.