Adaptive Coordinated Direct and Multi-RIS Transmissions for Ultrareliable Terahertz Systems

This paper investigates the outage probability of an adaptive coordinated direct and multi-RIS transmission for TeraHertz (THz) communication systems. Specifically, to tackle the connection loss due to pointing errors and severe attenuation in THz band, we propose two schemes that make use of a multi-RIS communication as a backup link to improve the reliability of the direct one. Invoking the two multi-RIS schemes, namely, the cooperative RIS (CR) and the opportunistic RIS (OR) schemes, exact and asymptotic outage expressions are obtained while accounting for small scale fading and non-zero boresight pointing errors. The accuracy of the analytical results is validated with Monte-Carlo simulations. The obtained results recognize a clear advantage of the proposed system compared with conventional standalone direct THz link. Thus, with carefully planned networks, enabling direct and multi-RIS cooperation for THz wireless systems can maintain sufficient coverage in sixth-generation (6 G) networks.