Active RIS-Aided Terahertz Communications with Phase Error and Beam Misalignment

Abstract: Terahertz (THz) communications will be pivotal in sixth-generation (6G) wireless networks, offering significantly wider bandwidths and higher data rates. However, the unique propagation characteristics of the THz frequency band, such as high path loss and sensitivity to blockages, pose substantial challenges. Reconfigurable intelligent surfaces (RISs) present a promising solution for enhancing THz communications by dynamically shaping the propagation environment to address these issues. Active RISs, in particular, can amplify reflected signals, effectively mitigating the multiplicative fading effects in RIS-aided links. Given the highly directional nature of THz signals, beam misalignment is a significant concern, while discrete phase shifting is more practical for real-world RIS deployment compared to continuous adjustments. This paper investigates the performance of active-RIS-aided THz communication systems, focusing on discrete phase shifts and beam misalignment. An expression for the ergodic capacity is derived, incorporating critical system parameters to assess performance. Numerical results offer insights into optimizing active-RIS-aided THz communication systems.