Ionospheric Narrowband and Wideband HF Soundings for Communications Purposes: A Review

Abstract

High Frequency (HF) communications through ionospheric reflection is a widely usedtechnique specifically for maritime, aeronautical, and emergency services communication withremote areas due to economic and management reasons, and also as backup system. Although longdistance radio links can be established beyond line-of-sight, the availability, the usable frequenciesand the capacity of the channel depends on the state of the ionosphere. The main factors thataffect the ionosphere are day-night, season, sunspot number, polar aurora and earth magneticfield. These effects impair the transmitted wave, which suffers attenuation, time and frequencydispersion. In order to increase the knowledge of this channel, the ionosphere has been soundedby means of narrowband and wideband waveforms by the research community all over the worldin several research initiatives. This work intends to be a review of remarkable projects for verticalsounding with a world wide network and for oblique sounding for high latitude, mid latitude,and trans-equatorial latitude