D.V. Ivanov1, V.A. Ivanov2, M.I. Ryabova3, R.R. Belgibaev4, V.V. Ovchinnikov5, A.V. Chernyadyev6

1-6 Volga State University of Technology (Yoshkar-Ola, Russia)

1 IvanovDV@volgatech.net; 2 IvanovVA@volgatech.net; 3 RyabovaMI@volgatech.net; 5 OvchinnikovVV@volgatech.net

Problem statement. Ionospheric shortwave (HF) radio communications face a significant challenge due to the variability in their operating frequency range and channel parameters. To enhance communication efficiency under the influence of radio channel variability and narrowband interferences, the creation of radio sensors based on software-defined radio is topical. These sensors are designed to analyze interference spectral density and identify available channels— those free from narrowband interference—using a threshold method. However, the notable irregularity in the spectrum often causes errors in determining channel availability, posing a problem to existing methods of assessing available channels. Employing the median filtering method with sliding filters of varying window sizes, namely small and large apertures, offers a potential solution to this problem by filtering the measured spectrum.

The aim of the research is to develop methods for assessing the availability of HF radio communication channels, considering variations in spectrum parameters such as fluctuations in the spectrum trend and significant outliers in minimum values.

Results. The study led to the development of models and methods for evaluating the availability of a composite HF radio channel, taking into account the characteristics of interference power spectral density (PSD), including a fluctuating trend and significant spikes at specific frequencies with minimum spectrum values. An investigation was carried out into the relationship between the standard deviation (RMS) of the moving median of PSD values and the length of the smoothing window at various times of the day. Analysis of the data revealed that with an increase in the smoothing window's length, the standard deviation decreases, reaching below 1 dB at a window size exceeding 315-340 samples (equivalent to 3 kHz per sample). It was found that employing a 0.95-1 MHz window for moving median filtering was appropriate in identifying a smooth trend. For assessing the occupancy threshold for partial and composite channels and subsequent analysis, the trend was removed from the PSD samples. The method addressed the challenge of setting a reference point for the threshold in each megahertz segment with random difference PSD. Experimental testing demonstrated a modest 4% increase in channel availability with a fourfold expansion in channel bandwidth. In areas of the power spectral density with variable trend levels, the method notably enhanced channel availability, showing an increase of up to 20% in the 3-5 MHz and 27-28 MHz ranges, and a striking increase of 28% to 40% in the 11-15 MHz and 24-25 MHz ranges, respectively.

Practical implications. The developed method has notably enhanced the efficacy of long-haul communication, particularly in challenging conditions characterized by fluctuating parameters within a composite radio channel and the impact of narrowband channel interferences. These findings pave the way for potential advancements in designing a sensor system with exceptionally low power requirements and economical costs, significantly benefiting network support within ionospheric sensing systems.

Ivanov D.V., Ivanov V.A., Ryabova M.I., Belgibaev R.R., Ovchinnikov V.V., Chernyadyev A.V. Development of methods for spectral monitoring of HF interferences for assessing the availability of ionospheric radio channels, considering the features of the varying spectrum. Radiotekhnika. 2023. V. 87. № 12. P. 64−77. DOI: https://doi.org/10.18127/j00338486-202312-08 (In Russian)

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