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
Recent research in HF radio communications and radar has focused on significantly expanding the frequency bandwidth of complex spread spectrum signals. This research faces challenges such as overcoming poorly understood negative phenomena, including variable multifactor dispersion of wave packets in the radio channel and variable interference. This study examines the basic physical and channel models of ionospheric propagation of radio waves and wideband wave packets in a variable dispersive ionospheric plasma. The need for this research stems from the fact that various types of dispersion distort wideband wave packets, hindering the advantages for long-haul radio communication systems and over-the-horizon radar. The aim of this work is to present models and approaches used to describe intra-mode variable ionospheric dispersion and analyze radio signal distortions in ionospheric plasma. In Part 1, we provide a scientific basis for the problem of expanding the frequency bandwidth of signals in HF radio systems using the presented models. We analyzed the effect of intra-mode dispersion on the structure function - impulse response (IR) of the ionospheric channel, including the chirping of the impulse response of a dispersive ionospheric channel. Calculations showed that the rate of the IR chirp increases with path length (geometric factor) and decreases with increasing operating frequency of the channel. The widening of IR chirplets due to intra-mode dispersion leads to pulse power losses, which, for NVIS traces and a 1 MHz channel bandwidth, reach 13-20 dB.
We also established the effect of reducing losses in regions where the type of dispersion changes. To model the effect in the region where the type of dispersion changes, we selected the chirp parameters observed in computational experiments for NVIS links at a relative channel frequency near 0.5 MUF, where the change in dispersion type occurred. The observed focusing effect showed an increase in IR power by approximately 10 dB in the region where the type of dispersion changes.
The practical significance of this work is manifested in developing an approach that integrates physical and channel models of wideband wave packet propagation in the ionosphere. This approach describes the types of intra-mode dispersion and methods to overcome them. Numerical analysis and studies of the mechanisms of normal and anomalous intra-mode dispersion in the ionospheric plasma identified their negative impacts on the structural function of the IR channel. We shall note, that it is highly reasonbable to consider these findings when designing advanced wideband ionospheric HF communication systems.
Иванов Д.В., Иванов В.А., Рябова М.И., Овчинников В.В. Эффекты дисперсии в ионосферных радиоканалах. Ч. 1. Модели распространения волновых пакетов в диспергирующих ионосферных каналах // Радиотехника. 2024. Т. 88. № 8. С. 111−126. DOI: https://doi.org/10.18127/j00338486-202408-11
Ivanov D.V., Ivanov V.A., Ryabova M.I., Ovchinnikov V.V. Dispersion effects in ionospheric radio channels. Part 1. Models of wave packet propagation in ionospheric dispersive channels. Radiotekhnika. 2024. V. 88. № 8. P. 111−126. DOI: https://doi.org/10.18127/j00338486-202408-11 (In Russian)