A Novel Quadrature Stream-Splitting Integrated SIC-Driven Multiple Access Scheme for Enhanced Performance Under Imperfect SIC

In recent years, several emerging multiple-access (MA) schemes have been proposed, each offering distinct advantages. Non-orthogonal MA (NOMA) and quadrature NOMA (Q-NOMA) are widely recognized for their ability to reduce inter-user interference through successive interference cancellation (SIC). Rate-splitting MA (RSMA) enhances interference management by partially decoding interference and treating the remaining interference as noise. Quadrature RSMA (Q-RSMA) builds on RSMA by leveraging quadrature dimensions to enable interference-free detection of the common stream, achieving an ever-increasing average sum-rate (ASR) as the signal-to-noise ratio improves, even under imperfect SIC conditions. Building upon these strengths, this paper proposes a novel MA scheme that integrates the quadrature separation approach of Q-RSMA, the stream-splitting method of RSMA, and the SIC-based interference reduction technique of NOMA/Q-NOMA, and therefore termed the quadrature stream-splitting integrated SIC-driven MA (Q-SSMA). To demonstrate the enhanced performance of Q-SSMA, closed-form expressions for outage probability (OP) and ASR are derived and corroborated through simulations. Numerical results show that Q-SSMA outperforms RSMA, Q-RSMA, NOMA, and Q-NOMA in both OP and ASR, while offering computational complexity comparable to NOMA.