Future Directions in Multiple Access for 6G: Emerging Paradigms and Insights

This work presents a comprehensive performance assessment of various multiple access (MA) schemes for downlink communication, with a focus on rate-splitting multiple access (RSMA), sparse code multiple access (SCMA), and power-domain non-orthogonal multiple access (PD-NOMA), in comparison to the traditional orthogonal multiple access (OMA) scheme. The study analyzes these schemes under imperfect decoding conditions, assessing their sum-rate, fairness, and outage performance. Simulation results show that SCMA achieves better sum-rate and outage performance than other MA schemes, even under conditions of imperfect decoding. Furthermore, RSMA provides better fairness at lower power levels, while SCMA achieves superior fairness at higher power levels. By integrating a thorough survey with simulation-based insights, this work underscores the distinct advantages of SCMA and RSMA, positioning them as promising candidates for future 6G wireless communication systems.