Abstract:
Rapid fluctuation of signals due to tropospheric scintillation with simultaneous occurrence of rain can become significant impairment along the propagation paths in satellite communication systems. When radio wave signal at higher frequency (especially at Ku-band and above) travels through the tropospheric layer in the tropics, it experiences absorption, scattering and a more severe degradation because of high frequency of occurrence of rainfall, high relative humidity and temperature. In this work, the relationship between scintillation and rain attenuation obtained from the slant path attenuation measurements at 12.25 GHz Ku-band satellite beacon measurement is presented. The analysis has been based on three years archived data from in-situ measurement using satellite beacon receiver automatic weather station at the Communication Research Laboratory (CRL), Department of Physics, the Federal University of Technology, Akure, Nigeria. The ITU-R 618-15 models have been used to estimate the scintillation intensity and scintillation fade depth at different percentage of time, as well as attenuation due to rain at different time percentages. Results are presented based on probability density function (PDF) of different scintillation parameters, cumulative distribution and probability density distribution of rain-induced attenuation at different percentages and testing the predicted values with real time rain attenuation at the study location. The results show that occurrence of high scintillation is dominant during rain events and, that short term hourly scintillation intensity and scintillation fade depth show far more variations than the monthly average scintillation intensities. Further result shows that at 0.01% of time in an average year, the cumulative distribution (CDF) of rain rate is about 116 mm/h with an equivalent rain attenuation of about 15.15 dB during the observed period. Also, the received signal strength (RSS) is about -74.5 dBm compared to the maximum transponder power of -81 dBm obtained from the geostationary satellite used. Hence, signal unavailability at
0.01% of the time is enormous in the presence of rain fade and tropospheric scintillation occurring simultaneously within the study location. However, a comparison of measured and estimated rain attenuation and scintillation intensity shows that the ITU-R Model underestimated both the rain fade and scintillation fade depth within the study location.
