Pointing-Error-Induced Fading in an Open-Loop THz Uplink with Hardware Impairments

Abstract: We analyze the open-loop mechanical tracking performance of a sub-Terahertz (sub-THz) and Terahertz (THz) uplink communication system. These high-frequency bands enable multi-gigabit links through large bandwidths and narrow beams, but require precise pointing to overcome spreading loss. A tracking system can be used to orient horn antennas toward mobile targets. We develop a mathematical model that captures the mechanical dynamics of a real tracking system, which includes motion latency and acceleration and velocity limits, to quantify pointing errors during satellite passes and integrate these effects into the link budget. We evaluate the trade-offs between beam directionality and pointing tolerance across different Low Earth Orbit (LEO) satellite trajectories and control strategies. The results link the hardware limitations to the communications performance, providing design guidelines for high-frequency Non-Terrestrial Network (NTN) uplink under practical mechanical constraints.