Maximum Effective Throughput for Uplink NOMA Systems With Practical Modulations

As a promising technology for future networks, non-orthogonal multiple access (NOMA) has drawn great attention for its enhanced throughput with massive connectivity. Most of the existing NOMA schemes employ the ideal information rate as the performance metric, assuming perfect successive interference cancellation (SIC), which may lead to suboptimal performance in practice. In this paper, by considering the imperfect SIC and practical modulation schemes, we propose a power control scheme for uplink NOMA systems with the aim of maximizing the effective throughput. To address this problem, we first analyze the symbol error probabilities of two users employing the quadrature amplitude modulation (QAM) scheme, and then a specific expression of the effective system throughput is provided, which considers both the error performance and the data rate. Considering the complicated effective throughput expression of the uplink NOMA design, we next derive a lower bound of the effective throughput and consequently obtain an efficient power control scheme in closed form by maximizing the lower bound of the effective throughput. Numerical results are provided to demonstrate the superiority of our proposed scheme.