Reconfigurable Intelligent Surface Aided TeraHertz Communications Under Misalignment and Hardware Impairments

TeraHertz (THz) communications are envisioned to help satisfy the ever high data rates demand with massive bandwidth in the future wireless communication systems. However, severe path attenuation, transceiver antenna misalignment, and hardware imperfection greatly alleviate the performance of THz communications. To solve this challenge, we utilize the recently proposed reconfigurable intelligent surface (RIS) technology and provide a comprehensive analytical framework of RIS-aided THz communications. More specifically, we first prove that the small-scale amplitude fading of THz signals can be exactly modeled by the fluctuating two-ray distribution based on recent measurements. Exact statistical characterizations of end-to-end signal-to-noise plus distortion ratio (SNDR) and signal-to-noise ratio (SNR) are derived. Moreover, we propose a novel method of optimizing the phase-shifts at the RIS elements under discrete phase constraints. Finally, we derive analytical expressions for the outage probability and ergodic capacity, respectively. The tight upper bounds of ergodic capacity for both ideal and non-ideal radio frequency chains are obtained. We provided Monte-Carlo simulations to validate the accuracy of our results. It is interesting to find that the impact of path loss is more pronounced compared to others, and increasing the number of elements at the RIS can significantly improve the THz communication system performance.