In this work, we investigate the impact of Doppler frequency shift on sub-terahertz low Earth orbit (LEO) satellite communications using OFDM transmission. To comprehensively evaluate the severity of the Doppler shift impact on sub-terahertz satellite-to-ground links, we first put together an evaluation framework that jointly accounts for major Doppler-induced and non-Doppler-induced signal impairments in such systems. We then compare and contrast three possible engineering approaches to deal with Doppler shift in such a communication system. Our study concludes that (i)~while just ignoring the Doppler effect in such high-frequency and high-mobility systems substantially compromises the performance and reliability, (ii)~most of the negative effects can be eliminated by implementing only a small set of low-complexity measures. We particularly show that even a single Doppler shift estimation over a 5-min-long satellite pass over the ground user location may be sufficient to ensure high performance throughout the entire connectivity period. Hence, while Doppler shift is an important effect to account for in sub-terahertz LEO satellite communications, it should not constitute a critical design challenge for these emerging systems.

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