Secure Transmission for THz-Empowered RIS-Assisted Non-Terrestrial Networks

TL;DR

This paper explores secure terahertz communication in non-terrestrial networks using RIS technology, deriving an ergodic secrecy rate expression and optimizing phase shifts to enhance security despite atmospheric and hardware imperfections.

Contribution

It introduces a novel model for THz-empowered RIS-assisted NTNs, deriving an approximate ESR expression considering atmospheric turbulence and phase errors, and proposes phase shift optimization algorithms for security enhancement.

Findings

The ESR expression accurately models the system under turbulence and phase errors.

Optimized RIS phase shifts improve secrecy rates even with high jitter.

Positive secrecy rate is achievable despite hardware and atmospheric imperfections.

Abstract

The non-terrestrial networks (NTNs) are recognized as a key component to provide cost-effective and high-capacity ubiquitous connectivity in the future wireless communications. In this paper, we investigate the secure transmission in a terahertz (THz)-empowered reconfigurable intelligent surface (RIS)-assisted NTN (T-RANTN), which is composed of a low-Earth orbit satellite transmitter, an RIS-installed high-altitude platform (HAP) and two unmanned aerial vehicle (UAV) receivers, only one of which is trustworthy. An approximate ergodic secrecy rate (ESR) expression is derived when the atmosphere turbulence and pointing error due to the characteristics of THz as well as the phase errors resulting from finite precision of RIS and imperfect channel estimation are taken into account simultaneously. Furthermore, according to the statistical and perfect channel state information of the untrustworthy receiver, we optimize the phase shifts of RIS to maximize the lower bound of secrecy rate (SR) and instantaneous SR, respectively, by using semidefinite relaxation method. Simulation results show that both the approximate expression for the ESR and the optimization algorithms are serviceable, and even when the jitter standard variance of the trustworthy receiver is greater than that of the untrustworthy one, a positive SR can still be guaranteed.