Analysis of Rain Fade Slope for Ka and V-Band Satellite Links in Southern England

Abstract

The fade slope of rain attenuation at Sparsholt, U.K. has been measured for a link with the ITALSAT F1 and F2 satellites at frequencies of 18.7, 39.6, and 49.5 GHz and compared with the corresponding ITU-R model. The model fits the data well visually with a tendency to be less accurate with increasing frequency due to the assumption of constant scaling of equiprobable attenuations being less accurate at higher frequencies. The probability distribution used in the model fails a chi-squared test for all confidence levels when compared with the data. Conditional statistics of fade slope on a diurnal and seasonal basis are also analyzed and reveal that the autumn season has higher fade slopes than any other, which can in part be attributed to the higher ratio of stratiform to convective rain in the autumn season. Fade slope was found to have slightly higher values during midday.

Fade Slope Statistics on a Slant Path at 50 GHz

“…3, there is an almost linear relationship between and for all time intervals, which is in agreement with (3). Nevertheless, the measured values are below the predicted ones for the lower attenuations.…”

“…Since this method is valid only up to 30 GHz, it needs to be verified at higher frequencies by comparing its predictions to experimental data. Specifically, only a few results have been published about fade slope statistics at -band frequencies [3], where mitigation techniques are even more necessary. Whereas at lower frequencies fade is mainly caused by rain, clouds contribute to the total path attenuation in the -band with significant values, as reported in [4] may also affect the statistics of fade slope, particularly for low attenuation values.…”

Statistics of rain attenuation revisited

“…Based on the experimental results described in [1] Figure 2a shows a comparison with the Student's-t distribution. Note the similarity with the ad-hoc distribution in [7] (8) which however was valid for the slope conditioned on the attenuation.…”

“…More recently, there has been considerable focus on details of the channel through rain, where the speed of change of attenuation is considered, expressed as a rain fade slope measured in dB/s [7,1]. The distribution of slopes were compared with an ad hoc distribution, while it is shown here that during the heavy fading periods the unconditional distribution is the well known Student's-t.…”

“…This opens the possibility of exact distributions of Doppler variations and of the recently studied rain fade slope, which must follow a Student's t-distribution with the Doppler spread as parameter. The theory is tested on experimental data published in [1]. …”