CHARACTERIZATION OF KU-BAND AMPLITUDE SCINTILLATION FOR SATELLITE COMMUNICATION OVER AKURE, NIGERIA

Abstract

Tropospheric amplitude scintillation has been reported as a significant cause of degradation to satellite communication systems operating at Ku-Band frequencies using small aperture antennas. Due to the dependence of amplitude scintillation on meteorological and link factors, it experiences significant spatio-temporal variation which must be statistically characterised for effective satellite link budgeting on any Earth-space path. A detailed experimental study of tropospheric amplitude scintillation on the Earth-space path over Akure, southwest Nigeria (7.17oN, 5.18oE, 358 m) was carried out using radio beacon signals from EutelSat W4/W7 satellite with concurrent measurement of meteorological parameters of temperature, pressure, humidity and rainfall rate. Beacon measurement was performed using spectrum analyser (Tektronix Y400 NetTek Analyzer) at 1-second integration time on the satellite downlink frequency of 12.254 GHz and path elevation 036oE; while meteorological parameters were measured at 1-minute integration time using Vantage Vue weather station equipped with integrated sensor suite (ISS). Extensive analysis involving time series, power spectral density, peak-to-peak excursion, cumulative distribution and probability density functions of scintillation amplitude and intensity have been performed on diurnal, seasonal and annual basis. Also, the dependence of scintillation on weather parameters was investigated and a semi-empirical model developed for scintillation analysis. Performance evaluation of the model was carried out through comparison with existing scintillation models and statistical distribution functions. Sub-annual analysis of scintillation amplitude and intensity was equally examined for worst month characterization. Results show that a cut-off frequency of 0.27 Hz performed optimally for scintillation extraction, and the existence of strong and weak scintillation regimes were observed during both dry and rainy seasons. Peak-to-peak scintillation amplitude exceeded 1.35 dB during at least 1% of one-minute intervals in each year, while variation of hourly scintillation intensity was well approximated by a lognormal distribution, although Gamma and Generalized Extreme Value (GEV) distributions were well followed also in most months. Developed location-based prediction models for scintillation intensity, enhancement and fades performed excellently well with R2 value of at least 0.9. Although the developed scintillation models mirror ITU-R and Karasawa models to a good extent; both and other temperate region – developed models under-predicted scintillation phenomenon over this location, which is an indication that scintillation effect is more severe in the tropics.