Hybrid Power-Frequency Multiple Access With SIC-Free for Holographic Reconfigurable Intelligent Surface-Based Systems

This paper proposes a hybrid power-frequency multiple access (HPMA) strategy to enhance the reliability, energy, and capacity of wireless communication systems. HPMA, a technique that reconciles all mutual benefits of orthogonal multiple access (OMA) and non-OMA (NOMA), removes the need for successive interference cancellation (SIC) and bypasses the user pairing inherent to NOMA. Focusing on holographic reconfigurable intelligent surfaces-aided systems servicing two users under imperfect channel estimation conditions, we establish theoretical frameworks for outage probability (OP) and ergodic capacity (EC), where both metrics are quantified with exact closed-form expressions and asymptotic analyses for scenarios with high signal-to-noise ratio (SNR) as well as for low-rate region cases. The former scenario provides insights into system diversity, modulation, and coding gains, and the ergodic slope; whereas the latter scenario elucidates trade-offs between energy and reliability and the method for maximizing energy-spectral efficiency. Numerical results demonstrate that HPMA outperforms conventional OMA and NOMA, improving OP in most SNR ranges in addition to enhancing EC and energy efficiency at low to moderate SNRs.