Short-Packet NOMA With User Pairing Over Fluctuating Nakagami-m Fading Under Imperfect SIC: Achievable Rate and BLER Analysis

In the era of sixth-generation (6G) and the Internet of Things (IoT), ultra-reliable and low-latency communication (URLLC) has emerged as a pivotal requirement, necessitating the use of short-packet communications (SPC) in the finite blocklength (FBL) regime. This paper investigates the performance of a downlink non-orthogonal multiple access (NOMA) system over fluctuating Nakagami- m fading channels, which effectively capture the complex interplay between multipath scattering and shadowing severity. To bridge the gap between theory and practice, our analysis accounts for the impact of imperfect successive interference cancellation (SIC) and residual interference. By leveraging the properties of Meijer G-functions, we derive exact and asymptotic closed-form expressions for two key performance metrics: the average achievable rate (AAR) and the average block error rate (ABLER). The accuracy of the derived analytical framework is rigorously validated through extensive Monte Carlo simulations, demonstrating a perfect alignment across various system parameters. Our numerical results provide critical insights into the reliability-latency trade-offs, revealing that while NOMA offers superior spectral efficiency, it exhibits a distinct reliability penalty compared to orthogonal multiple access (OMA) in the short-packet regime. Furthermore, the study identifies power allocation trade-offs and quantifies how increasing the blocklength and fading parameters can mitigate the effects of channel dispersion and hardware impairments. These findings offer a robust theoretical foundation for the design and optimization of high-reliability, low-latency NOMA-based wireless networks.