D.V. Ivanov1, V.A. Ivanov2, N.V. Ryabova3, V.V. Ovchinnikov4

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

Currently, wideband ionospheric HF radio communication is rapidly developing. It gains new advanced qualities due to the use of IT-technologies, state-of-the-art tools for sensor diagnostics of channels, which allow one to adapt systems to negative time varying effects in the channel. However, the expansion of the bandwidth of systems operating through the ionosphere is challenging and requires overcoming the negative effect of intramode dispersion and developing a methodology and a mathematical macromodel of a non-stationary multidimensional system. The research is addressed to the development of intelligent methods for overcoming dispersion distortions in HF communication systems that use a significant bandwidth expansion.

Paper presents a channel model of wideband ionospheric HF radio channels, which takes into account intramode dispersion of normal and anomalous types. It is shown that in the vicinity of the frequency where dispersion type changes, its parameter equals GDD = 0 and the dispersion distortions caused by the frequency dependence of the group delay significantly mitigate. This effect can be used for practical applications to expand the channel bandwidth without spending resources on overcoming dispersion distortions of wideband HF communication signals.

In the general case, overcoming dispersion involves the use of an equalization method that implements the principle of inverse filtration. For ionospheric wideband HF channels, paper presents generalized algorithms that implement the equalizer operation with the reinforcement machine learning to update the correcting channel model through a training period, which was selected based on experimental data.

To update the equalization model, we developed unique active radio channel sensor with inverse filtration and machine learning modes, which implements methods of intellectual analysis of experimental data for ionospheric radio channels, as well as naive prediction and reinforcement learning in real time. Studies showed that in the case of using wideband fast frequency hopping for communication, the intramode dispersion of the group delay causes additional random phase shift keying of the received symbols. Its demodulation can only be implemented with the use of the presented complex method for overcoming intramode dispersion. Thus, for communication systems with inverse filtration and fast frequency hopping, this effect can be assumed as a mechanism for increasing the structural secrecy.

Experimental studies proved the efficiency of the developed methods for overcoming the negative effect of intramode dispersion. Their use for dispersive HF channels with a bandwidth of 1 MHz cause a decrease in the duration of the impulse responses to the values typically observed in the absence of dispersion (~ 1 μs). Research findings showed that on the mid-latitude paths with a length of roughly 2.6 Mm, the use of a complex method for overcoming dispersion in HF radio channels with a bandwidth of up to 1 MHz, ensures energy secrecy close to 35 dB.

The research findings contribute to the achievement of new capabilities in improving noise immunity and secrecy for the state-of-the-art ionospheric wideband HF radio communication systems. The practical application of the findings of the research into dispersion distortions of wideband wave packets and the developed methods will allow operation of ionospheric communication systems over wideband HF radio channels at a guaranteed reliability, expanding their technical capabilities.

Ivanov D.V., Ivanov V.A., Ryabova N.V., Ovchinnikov V.V. New capabilities of wideband cognitive communication systems opera-
ting over ionospheric HF radio channels with intramode dispersion. Radiotekhnika. 2022. V. 86. № 11. P. 162−177.
DOI: https://doi.org/10.18127/j00338486-202211-23 (In Russian)

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