Error Performance of NOMA System With Outdated, Imperfect CSI, and RHI Over $\alpha-\mu$ Fading Channels.

This paper investigates the joint impact of residual hardware impairment (RHI) and outdated and imperfect channel state information (CSI) on the performance of NOMA-based vehicular networks over $\alpha$ - $\mu$ fading channels, while taking into account the effect of imperfect successive interference cancellation (ipSIC). Particularly, we present a novel pairwise error probability (PEP) expression with arbitrary $L$ users, which applies to most channels (e.g., Rayleigh, Rice, Nakagami- $m$ , and Weibull distributions). Closed-form and asymptotic PEP expressions are derived to characterize each user's performance in different scenarios. Following that, the PEP is used to evaluate the union bound on the bit error rate of NOMA users. Furthermore, the asymptotic PEP expression is employed to quantify the diversity order of each user. The analysis is supported by numerical and Monte Carlo simulation results. We show that each NOMA user's effective diversity order equals its order precisely. We further show that ipCSI has a significant influence on PEP performance in the presence of RHI, particularly for weak users, but has almost no effect in an ideal RF environment with the vehicles sitting motionless. In a mobile environment, however, the impact of ipCSI on PEP performance for all users is almost ignored no matter whether RHI exists or not. Additionally, regardless of whether ipCSI or pCSI is used, RHI has a clear influence on PEP performance.