Adaptive Modulation for Non-Orthogonal Multiple Access (NOMA) with Imperfect SIC

The increasing demand for high-capacity wireless communications has always been a challenge for researchers. Non-Orthogonal Multiple Access (NOMA) is one of the emerging schemes that can improve the capacity of wireless networks. In the power-domain NOMA, users share the same frequency and time but with different power levels. In this paper, we propose a novel adaptive modulation scheme for a NOMA-based wireless network to achieve better throughput efficiency and improve the system spectral efficiency by considering imperfect Successive Interference Cancellation (SIC). This scheme allocates the appropriate modulation orders by solving an optimization problem constrained by a maximum Bit Error Rate (BER). We investigate the BER and throughput calculations to assess the efficacy of the proposed scheme. The results show that our adaptive scheme greatly improves the spectral efficiency compared to the traditional fixed modulation NOMA systems, indicating its potential to satisfy the demanding performance standards of future wireless networks.