Diversity Analysis for Indoor Terahertz Communication Systems under Small-Scale Fading

Harnessing diversity is fundamental to wireless communication systems, particularly in the terahertz (THz) band, where severe path loss and small-scale fading pose significant challenges to system reliability and performance. In this paper, we present a comprehensive diversity analysis for indoor THz communication systems, accounting for the combined effects of path loss and small-scale fading, with the latter modeled as an $\alpha-\mu$ distribution to reflect THz indoor channel conditions. We derive closed-form expressions for the bit error rate (BER) as a function of the reciprocal of the signal-to-noise ratio (SNR) and propose an asymptotic expression. Furthermore, we validate these expressions through extensive simulations, which show strong agreement with the theoretical analysis, confirming the accuracy and robustness of the proposed methods. Our results show that the diversity order in THz systems is primarily determined by the combined effects of the number of independent paths, the severity of fading, and the degree of channel frequency selectivity, providing clear insights into how diversity gains can be optimized in high-frequency wireless networks.