Abstract
The refraction and apparent reflection of HF radio waves by the ionosphere enables long range HF radio communications. The ionosphere is a distinctly irregular medium that is mostly driven by solar activity. Ionospheric models are useful in the prediction of ionospheric behaviour and in the provision of data required for the analysis and forecasting of ionospheric propagation. This paper provides a compact review of HF radio propagation prediction techniques and approaches for HF communications. The paper also highlights the numerous approaches have been used to date in an attempt to estimate F2 usable frequencies. The review presented in this paper is inspired by the most recent advances in the field of ionospheric prediction and modelling.
Highlights
The forecasting of radio wave propagation is considered as an applied science
It is usually desirable for HF transmission to occur on a frequency as near to the maximum usable frequency over the path at any instant as is feasible under conditions prevailing in practice
Various propagation prediction models exist in the form of software to predict the propagation path loss at different frequencies as well as the maximum usable frequency (MUF), frequency of optimum transmission (FOT), lowest usable frequency (LUF) and take off angle (TOA)
Summary
The forecasting of radio wave propagation is considered as an applied science. for the past four to eight decades, models for long term forecasting of the median monthly conditions for HF radio propagation have represented an important tool for applied science and radio science and for geophysical researchers in their theoretical studies of the upper atmosphere [1,2,3]. The use of HF communication is preferred due to its relative simplicity, its capability to provide long range communication at low power without repeater base stations, its ease of development and its low cost [4]. The main purpose of radio propagation forecasting is to give advice in advance about the future reliability of frequency bands propagated by means of the ionosphere. This task is referred to as long-term prediction/forecasting and can be split into a geophysical one, forecasting of a model ionosphere, and one of optical-electromagnetic theory, resolution of the propagation problem [2]. There is no unique solution of the forecasting problem; the right effort has to be found in a compromise between the needs of the user or client and the available resources [2, 5]
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