The terahertz (THz) band is considered a key enabler for future 6G communications; However, its practical deployment is severely constrained by atmospheric attenuation, turbulence, and blockage in direct transmission links. Although intelligent reflecting surfaces (IRS) combined with multi-input multi-output (MIMO) techniques have been proposed to mitigate these issues, existing studies typically rely on simplified channel assumptions and do not jointly account for heterogeneous turbulence and hardware impairments. In this paper, we investigate the performance of an IRS-assisted MIMO THz communication system over atmospheric turbulence channels. A unified analytical framework is developed, where the transmitter-to-IRS and IRS-to-receiver links are modeled using Málaga and Gamma-Gamma distributions, respectively. The model further incorporates pointing errors and non-ideal IRS characteristics, including phase noise and discrete phase shifts. Based on this framework, closed-form expressions for the average bit error rate (BER) and outage probability are derived for both equal-gain combining (EGC) and maximal-ratio combining (MRC) schemes. The numerical results indicate that appropriate modulation techniques can improve performance, while pointing errors and turbulence effects have a significant impact on performance. Increasing the number of input and output ports also significantly improves system performance for all receiving schemes. Comparative analysis reveals that the MRC scheme offers a higher gain compared to the EGC scheme, typically achieving a 1-5 dB performance gain. Still, this advantage diminishes as the number of input ports increases. Meanwhile, the effects of phase noise and phase shift on the system performance are evaluated, showing that increasing phase noise from 0 to /4 causes an SNR penalty of approximately 3 dB. As phase noise and phase shift continue to decrease, their impact on system performance will gradually diminish and approach zero. Consequently, the performance effects due to phase shift and phase noise are weaker compared to the differences in system performance caused by variations in system parameters. These results provide useful insights into the impact of channel impairments and system configurations on IRS-assisted THz MIMO performance.
Wu et al. (Wed,) studied this question.