![]() ![]() In order to increase the knowledge of this channel, the ionosphere has been sounded by means of narrowband and wideband waveforms by the research community all over the world in several research initiatives. These effects impair the transmitted wave, which suffers attenuation, time and frequency dispersion. The main factors that affect the ionosphere are day-night, season, sunspot number, polar aurora and earth magnetic field. Although long distance radio links can be established beyond line-of-sight, the availability, the usable frequencies and the capacity of the channel depends on the state of the ionosphere. High Frequency (HF) communications through ionospheric reflection is a widely used technique specifically for maritime, aeronautical, and emergency services communication with remote areas due to economic and management reasons, and also as backup system.
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