D.V. Ivanov1, V.A. Ivanov2, V.V. Ovchinnikov3

1–3 Volga state university of technology (Yoshkar-Ola, Russia)

1 IvanovDV@volgatech.net, 2 IvanovVA@volgatech.net, 3 OvchinnikovVV@volgatech.net

Expanding the channel bandwidth presents new opportunities for enhancing the energy, structural covertness, and noise immunity of HF communication systems. The widespread adoption of IT technologies and sensor diagnostic tools has greatly augmented the capabilities of HF communications. Previous studies have explored methods such as deconvolution and equalization to overcome the negative dispersion phenomenon, enabling bandwidth expansion up to 1 MHz. Subsequent investigations have led to a hypothesis proposing the achievement of positive results in bandwidth expansion without the need for resource-intensive equalization, by harnessing HF radio channels with frequencies where dispersion type transitions. To verify this hypothesis, a thorough examination of the physical effect, taking into account key geophysical factors, was required. Therefore, the objective of this study was to explore the potential of leveraging the physical effect of intramode dispersion type transition to significantly expand the bandwidth of undistorted transmission in HF communications.

During the course of our research, we made a significant discovery: the communication signal's maximum bandwidth can be increased by an average of 2.5–25 times in the frequency range where the dispersion type undergoes a transition compared to channels operating at different frequencies. To validate our hypothesis, we developed a mathematical channel model that considers group delay dispersion in the vicinity of the point where the dispersion type transitions, taking into account a two-layered ionosphere (E and F layers). This model allowed us to establish relationships for estimating the undistorted transmission bandwidth by linking it to the phase dispersion parameter.

By utilizing the International Reference Ionosphere (IRI) model, we were able to determine the frequency dependencies of the intramode dispersion parameters and the undistorted transmission bandwidth at the point where the dispersion type transitions. Through numerical experiments using geophysical data from 2020, while considering varying conditions, we obtained criteria for identifying the intramode dispersion type transition for the 1F2 mode on paths ranging from 500 to 3500 km in length.

Analyzing the results of channel availability within the defined bandwidth limit, we observed that on Near Vertical Incidence Skywave (NVIS) links, undistorted transmission bandwidth of up to 200 kHz could be achieved with an availability rate of 0.9–1 during the day. For long-haul links spanning up to 3500 km, the undistorted transmission bandwidth reached 900 kHz, with an availability rate of 0.8–1.

These findings hold great potential for the development of advanced ionospheric wideband HF radio systems. These systems can serve as viable alternatives to satellite and tropospheric communications, employing spread spectrum signals that offer robust noise immunity and covert capabilities for HF systems.

Ivanov D.V., Ivanov V.A., Ovchinnikov V.V. Expanding undistorted transmission bandwidth for HF communications by leveraging the physical effect of intramode dispersion type transition. Electromagnetic waves and electronic systems. 2023. V. 28. № 5. P. 49−60. DOI: https://doi.org/10.18127/j15604128-202305-06 (in Russian)

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