D.V. Ivanov1, V.A. Ivanov2, M.I. Ryabova3, V.V. Ovchinnikov4

1-4 Volga State University of Technology (Yoshkar-Ola, Russia)

1 IvanovDV@volgatech.net; 2 IvanovVA@volgatech.net; 3 RyabovaMI@volgatech.net; 4 OvchinnikovVV@volgatech.net

Reliable and secure data transmission in the HF range is a critical need for a broad spectrum of users, including both civil and government services. However, ionospheric HF channels present challenges such as limited bandwidth due to intramode dispersion and variability in their structural functions over slow geophysical time scales. This work aims to analyze the impact of intramode dispersion in wideband ionospheric channels, along with proposing methods and tools to mitigate its effects and enhance the covertness of wideband HF communication systems. The paper introduces an equalization technique based on inverse filtering, optimized for a wide bandwidth of up to 1 MHz. Analysis showed that reliable, secure data transmission is feasible primarily under single-mode propagation conditions. The experiments investigated the effect of dispersion on compressed wideband signals and assessed the impact of dispersion correction on signal compression results. Experimental findings on the added covertness and energy gain achieved through intramode dispersion correction demonstrated a power gain of approximately 44 times, significantly improving the energy covertness of data transmission systems. Additionally, the study experimentally proved an increase in the structural covertness of the system. These findings suggest that detecting wideband signals with bandwidths exceeding the channel coherence bandwidth becomes increasingly difficult, making it nearly impossible to demodulate such signals without precise knowledge of the channel’s frequency response and its equalization. A method for wideband HF communication under intramode dispersion conditions is presented. The practical significance of this work lies in demonstrating that wideband HF communication can serve as a viable alternative to satellite and tropospheric communication, offering high noise immunity and enhanced transmission covertness. Using an adaptive equalizer can further improve communication reliability, covertness, and reduce power consumption for both short- and long-haul comminications.

This work was supported by the grant 22-19-00073 from the Russian Science Foundation

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