Modeling and analysis for dynamical Doppler shifts on terahertz communication signals propagating in inhomogeneous hypersonic plasma sheath

Previous studies have shown that terahertz (THz) signals could penetrate hypersonic plasma sheaths. Thus, it is considered to be a potential solution to the “blackout” problem. Nevertheless, although previous studies have systematically revealed the signal transmission characteristics in hypersonic plasma sheaths and the influence of vehicle parameters on the communication performance, the coupling mechanism between the dynamical time-varying plasma sheath flow field and Doppler shift of THz communication signals has rarely been investigated. In this study, a layered medium model was developed to investigate the characteristics and the mechanisms for the Doppler shift in dynamical hypersonic plasma environments. The results revealed that the total Doppler shifts could be up to several megahertz (MHz), in which the Doppler shift yielded by the inhomogeneous flow field of the hypersonic plasma sheath could also reach the magnitude of several MHz. It indicates that the inhomogeneous flow field is an important mechanism for the communication capacity of Doppler shift. The dynamical evolution of the flow field yields the fluctuation of the total Doppler shift. The dynamical Doppler frequency shifts could have serious impacts on the signal demodulation, channel estimation, synchronization, and the communication capacity of the onboard system.