Numerical modeling on the bit error rate of EHF communication in time-varying hypersonic plasma sheath

Abstract

Plasma sheaths enveloping hypersonic vehicles could yield a communication blackout. Many previous studies have shown that the electromagnetic wave in an extremely high frequency (EHF) band could penetrate a hypersonic plasma sheath effectively. In other words, the EHF communication could be a potential solution to the communication blackout problem. Nevertheless, most of those works used to concern only the EHF signal attenuation. In addition, those works normally treated plasma sheaths as a static plasma layer. However, plasma sheaths always keep evolving. In the present study, the modulated EHF signal propagation in a time-varying plasma sheath was investigated numerically. The plasma sheath was obtained with a hypersonic hydrodynamical model that has been utilized in previous studies. The EHF signal propagation was modeled based on theories of geometrical optics. The frequencies studied are 94, 140, and 225 GHz. The investigation revealed that not only signal attenuation but also the phase shifts for carrier waves vary with time. Their impact on the bit error rate (BER) of the EHF communication system was studied numerically. The modulation modes concerned in the present study are 2ASK, 2PSK, 4QAM, and Non-Coherent demodulation 2FSK (NC-2FSK). According to the study, the BER keeps varying with time. This study also showed that the BER is impacted by the carrier frequency, modulation mode, and the demodulation method. According to the comparison and the analysis, the suggested modulation modes are 2PSK and 4QAM at the carrier frequency of 140 GHz, which could lead to smaller and more stable BER for the EHF communication system utilized by hypersonic vehicles.