  Uncrewed aerial vehicles (UAVs) have attracted recent attention for
sixth-generation (6G) networks due to their low cost and flexible deployment.
In order to maximize the ever-increasing data rates, spectral efficiency, and
wider coverage, technologies such as reconfigurable intelligent surface (RIS)
and non-orthogonal multiple access (NOMA) are adapted with UAVs (UAV-RIS NOMA).
However, the error performance of UAV-RIS NOMA has not been considered, yet. In
this letter, we investigate the error probability of UAV-RIS NOMA systems. We
also consider the practical constraints of hardware impairments (HWI) at the
transceivers, inter-cell interference (ICI), and imperfect successive
interference cancellation (SIC). The analytical derivations are validated by
Monte-Carlo simulations. Our results demonstrate that our proposed system
achieves higher performance gain (more than 5 dB with increasing the number of
RIS elements) with less error probability compared to UAVs without RIS.
Moreover, it is found that the HWI, ICI, and imperfect SIC have shown a
negative impact on the system performance.
