ДЕКОНВОЛЮЦИЯ ШИРОКОПОЛОСНОГО КВ-СИГНАЛА, ИСКАЖЁННОГО ПОЛЯРИЗАЦИОННОЙ И ЧАСТОТНОЙ ВНУТРИМОДОВОЙ ДИСПЕРСИЕЙ
Authors: Иванов Д.В. , Иванов В.А. , Рябова Н.В. , Овчинников В.В. 
Published: February 2025

Исследования относятся к области распространения широкополосных волновых пакетов в ионосферном КВ-радиоканале. Решалась задача деконволюции широкополосного КВ-сигнала, искажённого действием поляризационной и частотной внутримодовой дисперсии при его распространении в каналах с полосой 1 МГц из диапазона одномодового распространения. Учитывалось, что в процессе обработки сигнала методом деконволюции возникают ошибки, приводящие к уменьшению отношения сигнал/шум. Негативное влияние на данное отношение оказывает также изменчивость среды распространения сигнала. Для преодоления изменчивости использовался метод адаптации. Его верификация потребовала разработки экспериментального макета, реализующего метод адаптивной деконволюции. На основе полученных на радиотрассе о. Кипр – г. Йошкар-Ола экспериментальных данных доказано, что применение в КВ-диапазоне адаптивной деконволюции позволяет корректировать изменчивую внутримодовую поляризационную и частотную дисперсию. Однако при этом канальные шумы увеличивают своё действие.

Introduction. HF communication is rapidly developing due to the high possibilities of digital methods of signal synthesis and processing, as well as the widespread use of machine learning methods. This has risen the research into the application of wideband signals with bandwidth significantly greater than the channel coherence bandwidth. In the problem of wideband HF communication, deconvolution serves as a method for correcting dispersion distortions of signals, allowing one to extract the emitted (not distorted) signal from the received distorted signal samples. The aim of the research was the development of an advanced deconvolution principle to solve the problem of correction for dispersion distortions of spread spectrum signals corrupted by polarization and frequency intramode dispersion of the medium, as well as development of the corrector facility and its experimental verification. Theory foundations and methods. Theoretical foundations of the deconvolution method are supproted by the channel model of the ionospheric propagation of HF signals. The practical application of deconvolution invloves experimental measurement of the channel frequency response. The adaptive equalizer, which implements the deconvolution function, implies the modification of this procedure, and requires the use of periodic testing a frequency-ordered set of subchannels and equalizer training. In our case, testing is carried out with the use of the LFMCW (Linearly Frequency Modulated Continuous Wave) signal, which allows to adequately solve the problem of estimating the frequency response for adjacent subchannels from a wide equalizer operating bandwidth. The frequency response samples are measured experimentally, and therefore they are contaminated with errors and channel interferences. Thus, we analyzed the energy losses of a wideband HF signal due to a rise in the noise level during deconvolution. Experiments. To verify the advanced principle of adaptive deconvolution, we carried out experiments on the mid-latitude radio propagaiton path Cyprus-to-Yoshkar-Ola of 2600 km length. There was used LFMCW ionosonde developed at the Volga state university of technology with the use of USRP hardware platform supported by software-defined radio (SDR) technology, and the SDR-equalizer developed on the same platform for inverse filtration of the received signal. Research findings and conclusion. Research findings showed the efficiency of the adaptive equalization method for channels with a 1 MHz bandwidth from the single-mode propagation range. Studies of the energy losses due to frequency response contamination showed that the energy losses from inverse filtration in a 1 MHz channel were roughly 5 dB. It was shown that the developed principle of deconvolution based on adaptive equalization allows to correct for the negative effect of variable polarization and frequency intramode dispersion in wideband ionospheric HF radio channels. Impulse response of a channel with a 1 MHz bandwidth decreased their duration from 15-29 μs to theoretical values of 1 μs. However, deconvolution rises losses in the signal-to-noise ratio, which in experiments reached 5 dB. Experimental and theoretical estimates showed that the energy gain due to the use of spread spectrum signals will reach 35 dB if the data rate is 100 bit/s and carrier bandwidth is 1 MHz.