LAUSR

This letter considers an intelligent reflecting surface (IRS)-assisted terahertz (THz) communication system in the presence of an arbitrary number of colluding/non-colluding eavesdroppers (Eves). Although the instantaneous channel state information (CSI) of the legitimate user (Bob) is assumed to be available, the IRS with discrete phase shifters cannot achieve optimal phase shifts, and thus Bob suffers from phase shift quantization errors. By taking into account the availability of the statistical CSI of Eves, pointing errors caused by highly-directional THz antennas, and the phase shift quantization errors, new expressions for the secrecy capacity in both cases of Eves are derived. The accuracy of the expressions is then verified by Monte-Carlo simulations. These expressions are used to investigate the impacts of pointing errors and quantization errors on the physical layer security of IRS-assisted THz systems in the presence of colluding and non-colluding Eves.