A global model for wideband HF skywave propagation

Modern communications techniques employing digital signals, wide bandwidths and adaptive methods to combine multiple skywave returns coherently perform better under strong multipath conditions. In the design of a point-to-point HF communications link these conditions require, in addition to the received signal strength, information concerning: (1) the number of returns, (2) their relative delays, (3) delay dispersion, (4) Doppler shift and (5) Doppler smears. An HF propagation model is described which is suitable for the prediction of these parameters as a function of operating frequency, range, geographical location, time-of-day, season, and sunspot number. The diurnal, seasonal, geographical and solar-cycle variations of the parameters are obtained from their relationship to the same variations in the critical frequencies and heights of the D, E, F1 and F2 layers.