Performance Analysis of a STAR-IRS-Assisted THz-Enabled Multi-User Communication System

In this paper, we propose a simultaneously transmitting and reflecting intelligent reflecting surface (STAR-IRS) assisted multi-user communication system in the terahertz (THz) band. To overcome the potential blockage of direct links from the base station (BS) towards users or the possibility of users located out of the reach of the BS, the STAR-IRS assisted link can help enhancing the performance of the system. We derive closed-form expressions for the signal-to-noise ratio (SNR) outage probability for optimal and non-optimal STAR-IRS phase shifts with considering the users' statistical distribution within the service area. We conduct our analysis assuming the combined <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha-\mu$</tex> distribution, pointing errors, and molecular absorption that are inherent in THz transmission. The derived expressions are validated through Monte Carlo simulations and the effect of various system parameters on the outage probability is studied. Results show that the proposed system can achieve acceptable outage performance even with the existence of phase shift errors. Moreover, the performance can be further enhanced with increasing the number of STAR-IRS elements, which is practical in the THz band due to the very small wavelength.