On the Study of Multiuser Mixed Dual-Hop RF/THz Systems

Abstract

A multiuser mixed radio frequency/terahertz (MRFTHz) system is studied, where the multiple RF channels experience <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\eta$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> fading and the THz channel obeys <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu _{1}$</tex-math></inline-formula> fading with pointing errors (PEs). Both fixed-gain (FG) amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered in the relay. Firstly, the exact expressions of the cumulative distribution functions of the overall signal-to-noise ratio under AF and DF schemes are derived. On this basis, the Fox's H-function (FHF) and bivariate FHF are used to obtain exact analytical expressions of the outage probability (OP), average bit error rate, and average channel capacity. Additionally, the asymptotic results at high signal-to-noise ratios (SNRs) are provided to gain the system's diversity order (DO). Results show that the DOs of the AF and DF relaying systems are decided by the PEs and channel fading parameters (FPs). In addition, considering the FG AF relaying and multi-antenna scenarios, the asymptotic OP at high SNRs is derived, which obtaining the DO is determined by the numbers of the antenna, PEs, and FPs. Finally, we apply the Monte Carlo simulations to verify numerical results. Results show that the path loss, PEs, FPs, and the number of users can significantly affect the proposed multiuser MRFTHz system.