High-Altitude Platform Station-Aided Terahertz Satellite Communication Systems with Hardware Impairments
The utilization of terahertz (THz) frequencies in satellite-aerial-ground communication systems stands out as a promising solution to accomplish both global connectivity and extreme data rates requirements of the sixth-generation networks. In the current literature, the impact of non-ideal equipment on the performance of THz satellite-aerial-ground communication systems remains unexplored, which is critical for practical implementations. Hence, this paper analyzes the performance of high-altitude platform station (HAPS)-aided THz satellite communication system in the presence of $α$-$μ$ fading, pointing errors, absorption loss, and hardware impairments for different atmospheric conditions. In the system of interest, it is assumed that variable-gain amplify-and-forward protocol is utilized at HAPS nodes (systems), and the HAPS system, which provides the maximum end-to-end signal-to-noise ratio (SNR), is selected for transmission. To evaluate the outage, asymptotic outage, and ergodic capacity bounds for the system, the probability density function, cumulative distribution function (CDF), and asymptotic CDF related to the upper bound of the end-to-end SNR are obtained. By using these statistics, the effects of hardware impairment levels, zenith angles, and atmospheric conditions on the system performance are examined. The results have shown that hardware impairments cause power loss in outage performance and reduce the system capacity. Moreover, it is demonstrated that the outage probability depends on either fading or pointing error characteristics in high SNR region and also that the system performance almost remains the same for lower zenith angles in HAPS-to-ground link regardless of the atmospheric conditions.